Part B Individual Engineering Project Report - 11011794

Sven Cumner Optimisation of Turbocharger Wastegate Design 11011794
UNIVERSITY OF THE WEST OF ENGLAND
FACULTY OF ENVIRONMENT AND TECHNOLOGY
ENGINEERING DESIGN AND MATHEMATICS
Individual Engineering Project (Part B) Report
Optimisation of Turbocharger Wastegate Design
Student: Sven Cumner
Student Number: 11011794
Project Supervisor: Dr Changho Yang
Award: MEng Motorsport Engineering
No industrial links or support associated with this project
Total number of pages: 74
Number of core content pages: 66

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Abstract
Turbocharger boost control methods were investigated, citing several literature resources to
gather a profile on these methods, leading to a more in-depth discussion of wastegate
systems. It was postulated that the age-old, standard flapper-door style internal wastegate
system has not been improved and optimised to the same level as other areas of the
turbocharger. In this modern era of highly developed powertrain systems, this seemed like an
over-looked area of turbocharger design that deserved more analysis. Several concept designs
for improved wastegate valves were drawn up and transferred in to 3D Solidworks CAD
models. These models were then transformed in to fluid flow domains for analysis in the
ANSYS CFD software package.
It was found that no perfect valve had been modelled, but that two of the concept valves did
show improvements over the standard design, albeit in different ways. A ‘Concave Cone’
valve was found to improve the quality of the flow from the turbine outlet of the
turbocharger, whereas an up/down ‘Wedge’ valve was found to reduce flow separation from
the upper and lower walls of the flow domain.

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Contents
Abstract......................................................................................................................................ii
List of Figures............................................................................................................................v
1. Introduction: Origins and Aims .............................................................................................1
1.1 Why was this study undertaken?......................................................................................1
1.2 What are the aims of the project?.....................................................................................2
2. Boost Control.........................................................................................................................3
2.1 Why Is Boost Control Needed?........................................................................................4
2.2 Boost Control Strategies...................................................................................................4
2.2.1 Fixed or Geometrical Boost Control.........................................................................5
2.2.2 Dynamic Boost Control ............................................................................................6
2.2.3 Cold-side Boost Controls..........................................................................................7
2.2.4 Hot-side Boost Controls..........................................................................................11
2.2.5 Wastegates ..............................................................................................................13
2.2.6. Wastegate Valve Control Strategies ......................................................................16
3. Premise of the Experiment...................................................................................................17
3.1 Why does it need improvement? – Part open control ....................................................17
4. Simulation Model Creation and Setup.................................................................................18
4.1 CAD geometry (Solidworks) .........................................................................................18
4.2 CFD Simulation (ANSYS).............................................................................................29
4.2.1 CFX-Pre: Setup/Determining the Flow Parameters................................................29
4.2.2 CFX-Solver: Obtaining the Solution ......................................................................31
4.2.3 CFD-Post: Viewing the results ...............................................................................32
5. Analysing the Factory System .............................................................................................33
5.1 Factory Turbo with Wastegate Closed...........................................................................33
5.2 Factory Turbo With Wastegate Valve Open Ten Degrees.............................................35
5.3 Factory Turbo With Wastegate Valve Open Twenty Degrees.......................................37
6. Analysing The Proposed Valve Designs..............................................................................39
6.1 Hemisphere Valve..........................................................................................................39

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6.1.1 Ten Degrees Open (Hemisphere)............................................................................39
6.1.2 Twenty Degrees Open (Hemishpere)......................................................................41
6.2 Cone Valve.....................................................................................................................43
6.2.1 Ten Degrees Open (Cone) ......................................................................................43
6.2.2 Twenty Degrees Open (Cone) ................................................................................45
6.3 Concave Cone Valve......................................................................................................47
6.3.1 Ten Degrees Open (Concave).................................................................................47
6.3.2 Twenty Degrees Open (Concave)...........................................................................48
6.4 Wedge Valve..................................................................................................................50
6.4.1 Ten Degrees Open (Wedge – up/down)..................................................................50
6.4.2 Twenty Degrees Open (Wedge – up/down)............................................................51
6.4.3 Twenty Degrees Open (Wedge rotated 90 degrees – left/right) .............................53
6.5 Pyramid Wedge Valve ...................................................................................................55
6.5.1 Ten Degrees Open (Pyramid) .................................................................................55
6.5.2 Twenty Degrees Open (Pyramid) ...........................................................................56
6.6 Preliminary Conclusions: Which Valve Design is Best?...............................................58
7. Valve Seat Design Analysis.................................................................................................59
7.1 Chamfer Seat with Concave Cone Valve.......................................................................59
7.2 Chamfer Seat with Wedge Valve...................................................................................60
7.3 Radius Seat with Concave Cone Valve..........................................................................60
7.4 Radius Seat with Wedge Valve......................................................................................61
7.5 Preliminary Conclusions: Which Valve Seat is Best? ...................................................61
8. Discussion and Conclusions ................................................................................................62
9. Recommendations for further work.....................................................................................63
Bibliography ............................................................................................................................64
Appendices...............................................................................................................................66
Appendix A (Garrett, 2015) .................................................................................................66

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List of Figures
Figure 1: A typical modern turbocharger, the Garrett GT1544. (Zhejiang Rongfa Motor
Engine Co., Ltd., unknown).......................................................................................................3
Figure 2: Loss of traction and damaged drivetrain components – two important reasons for
the existence of boost control. (The Art Mad, unknown) (unknown, unknown).......................4
Figure 3: Turbocharger operational diagram (MazdaRotary, unknown)...................................5
Figure 4: Compressor flow map showing the defined limits of a compressors flow capability
(Garrett, 2015)............................................................................................................................7
Figure 5: Diagram of blow-off valve. When pressure limit is reached, valve opens (shown on
right). (GReddy, 2015)...............................................................................................................8
Figure 6: A typical butterfly valve to control air-flow in an engine (unknown, 2006) .............9
Figure 7: An intake restrictor, decreasing the intake diameter of a turbocharger compressor
inducer. (Force-D Rally Team, 2012)......................................................................................10
Figure 8: Diagrams depicting theoretical effects of exhaust piping being too small (top),
correctly sized (bottom left), and too big (bottom right). Each white area represents an
exhaust gas pulse. (Team Integra, 2002) .................................................................................11
Figure 9: Diagrams of a VNT Turbocharger, as part of a Volvo 5-cylinder diesel powertrain.
(Volvo, 2010)...........................................................................................................................12
Figure 10: View of a typical internal wastegate setup, looking at the mounting flange face
with turbine exducer (left) and wastegate system (right). (Sonic Performance, unknown) ....14
Figure 11: Example of an external wastegate setup (bottom of image). (Radium Engineering,
2010) ........................................................................................................................................15
Figure 12: Turbine housing, viewed from the exducer side with wastegate at top centre of
image........................................................................................................................................18
Figure 13: The wastegate valve (disconnected from its external pressure actuator) opened to
two arbitrary angles..................................................................................................................19
Figure 14: Photograph showing relation to turbine housing inlet (right) and wastegate port
(middle) with wastegate valve swung all the way round for clarity........................................19
Figure 15: Creation and positioning of the main reference circles for the flange profile........20
Figure 16: Further reference points added to sketch................................................................20
Figure 17: The final flange profile sketch, a complex amalgamation of profiles to match the
engineering drawing.................................................................................................................21

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Figure 18: The turbine inlet was modelled, seen in context on the left and in profile on the
right..........................................................................................................................................21
Figure 19: Lofted cut path sketched in to top of block (left), and trying to capture the created
cut flow path (right) .................................................................................................................22
Figure 20: Completed turbine housing, without the wastegate valve. Solidworks model (left),
reference image (right) (Engine Basics, 2010). .......................................................................22
Figure 21: Solidworks model of factory wastegate valve........................................................23
Figure 22: Valve arm in place in turbine housing, with construction lines to check
centralisation of mounting pin hole .........................................................................................23
Figure 23: Details and images of the hinge mate used to control the wastegate valve opening
angle (set to 20 degrees here)...................................................................................................24
Figure 24: Side view of factory valve open to 10 degrees. Turbine housing set to translucent.
..................................................................................................................................................24
Figure 25: Original pen and paper sketches for altered valve designs ....................................25
Figure 26: Hemi-spherical valve..............................................................................................26
Figure 27: Cone valve (left) and concave cone valve (right)...................................................26
Figure 28: Wedge valve, shown in two different views for clarity. ........................................27
Figure 29: Pyramid wedge valve, shown in two different views for clarity............................27
Figure 30: Turbine housing assembly inside the 'mould block'...............................................28
Figure 31: Wireframe model of a completed CFD domain. ....................................................28
Figure 32: Wastegate flow parameters (left), turbine flow parameters (right)........................30
Figure 33: Flow boundaries on the turbine housing domain ...................................................31
Figure 34: CFX-Solver notice message indicating flow reversal ............................................32
Figure 35: Diagram showing model orientation references.....................................................32
Figure 36: Solidworks model of factory turbo setup with wastegate closed ...........................33
Figure 37: Side view of the closed factory wastegate valve, viewed through a translucent
turbine housing.........................................................................................................................33
Figure 38: Velocity streamlines of turbine exducer (factory valve closed).............................34
Figure 39: Pressure contour plot (factory valve closed) ..........................................................34
Figure 40: Velocity streamlines of turbine exducer (factory valve open 10 degrees).............35
Figure 41: Velocity streamlines of wastegate valve (factory valve open 10 degrees).............35
Figure 42: Temperature contour plot (factory valve open 10 degrees) ...................................36
Figure 43: Pressure contour plot (factory valve open 10 degrees) ..........................................36

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Figure 44: Velocity streamlines of turbine exducer (factory valve open 20 degrees).............37
Figure 45: Velocity streamlines of wastegate valve (factory valve open 20 degrees).............37
Figure 46: Temperature contour plot (factory valve open 20 degrees) ...................................38
Figure 47: Pressure contour plots (factory valve open 20 degrees).........................................38
Figure 48: Velocity streamlines of turbine exducer (hemi valve open 10 degrees) ................39
Figure 49: Velocity streamlines of wastegate valve (hemi valve open 10 degrees)................39
Figure 50: Temperature contour plot (hemi valve open 10 degrees).......................................40
Figure 51: Pressure contour plot (hemi valve open 10 degrees)..............................................40
Figure 52: Velocity streamlines of turbine exducer (hemi valve open 20 degrees) ................41
Figure 53: Velocity streamlines of wastegate valve (hemi valve open 20 degrees)................41
Figure 54: Temperature contour plot (hemi valve open 20 degrees).......................................42
Figure 55: Pressure contour plot (hemi valve open 20 degrees)..............................................42
Figure 56: Velocity streamlines of turbine exducer (cone valve open 10 degrees).................43
Figure 57: Velocity streamlines of wastegate valve (cone valve open 10 degrees) ................43
Figure 58: Temperature contour plot (cone valve open 10 degrees) .......................................44
Figure 59: Pressure contour plot (cone valve open 10 degrees) ..............................................44
Figure 60: Velocity streamlines of turbine exducer (cone valve open 20 degrees).................45
Figure 61: Velocity streamlines of wastegate valve (cone valve open 20 degrees) ................45
Figure 62: Temperature contour plot (cone valve open 20 degrees) .......................................46
Figure 63: Pressure contour plot (cone valve open 20 degrees) ..............................................46
Figure 64: Velocity streamlines of turbine exducer (concave valve open 10 degrees) ...........47
Figure 65: Velocity streamlines of wastegate valve (concave valve open 10 degrees)...........47
Figure 66: Velocity streamlines of turbine exducer (concave valve open 20 degrees) ...........48
Figure 67: Velocity streamlines of wastegate valve (concave valve open 20 degrees)...........48
Figure 68: Temperature contour plot (concave valve open 20 degrees)..................................49
Figure 69: Pressure contour plot (concave valve open 20 degrees).........................................49
Figure 70: Velocity streamlines of turbine exducer (wedge valve open 10 degrees)..............50
Figure 71: Velocity streamlines of wastegate valve (wedge valve open 10 degrees) .............50
Figure 72: Velocity streamlines of turbine exducer (wedge valve open 20 degrees)..............51
Figure 73: Velocity streamlines of wastegate valve (wedge valve open 20 degrees) .............51
Figure 74: Temperature contour plot (wedge valve open 20 degrees) ....................................52
Figure 75: Pressure contour plot (wedge valve open 20 degrees) ...........................................52
Figure 76: Velocity streamlines of turbine exducer (rotated wedge open 20 degrees) ...........53

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Figure 77: Velocity streamlines of turbine exducer (rotated wedge open 20 degrees) ...........53
Figure 78: Temperature contour plot (rotated wedge open 20 degrees)..................................54
Figure 79: Pressure contour plot (rotated wedge open 20 degrees).........................................54
Figure 80: Velocity streamlines of turbine exducer (Pyramid valve open 10 degrees)...........55
Figure 81: Velocity streamlines of wastegate valve (Pyramid valve open 10 degrees) ..........55
Figure 82: Velocity streamlines of turbine exducer (pyramid open 20 degrees).....................56
Figure 83: Velocity streamlines of wastegate valve (pyramid open 20 degrees) ....................56
Figure 84: Temperature contour plot (pyramid open 20 degrees) ...........................................57
Figure 85: Pressure contour plot (pyramid open 20 degrees)..................................................57
Figure 86: Velocity streamlines for turbine exducer (left) and wastegate valve (right)
(Chamfer seat with concave cone valve) .................................................................................59
Figure 87: Velocity streamlines of turbine exducer (left) and wastegate valve (right)
(Chamfer seat with wedge valve) ............................................................................................60
Figure 88: Velocity streamlines of turbine exducer (left) and wastegate valve (right) (Radius
seat with concave cone valve)..................................................................................................60
Figure 89: Velocity streamlines of turbine exducer (left) and wastegate valve (right) (Radius
seat with wedge valve).............................................................................................................61

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1. Introduction: Origins and Aims
1.1 Why was this study undertaken?
With tighter and tighter regulations regarding vehicle emissions, and with an ever
growing need to downsize engine capacities, turbocharging offers the chance to give a small
engine the power of a large one. In motorsport, turbocharging has traditionally been used
primarily to give significant power increases to race car powertrains, greatly increasing the
vehicles competitiveness on the track. In the modern road and motorsport vehicle industry,
downsizing engines results in lower emissions and lower fuel consumption, two important
aspects for the longevity of the environment. For these reasons, it is a vital, growing area of
modern engine development in ordinary road cars, as well as top tier racing cars. It is,
therefore, greatly beneficial for the modern motorsport engineer to have a thorough
understanding of how these turbocharged engines work and how they are designed and
developed to give such beneficial increases in efficiency and overall performance.
A thorough understanding of the technologies is required to be able to design a system
that performs to the best capabilities of each component in that system. There are drawbacks
to turbocharging, such as vastly increased intake charge temperatures and requiring more
space within the engine-bay to house the additional system components. Turbocharging is
also an expensive development/modification - whether it is on new or existing engines - and
the addition of a turbocharger results in a raft of other changes and modifications that need to
be done to other parts of the engine. Knowing how and why the components in the system
work is essential if the system is to be developed as efficiently as possible and these
drawbacks are to be minimised.
The wastegate valve is an overlooked part of turbocharger design, and whilst the gains
of optimisation may not be large, every aspect of a modern turbocharger should be refined
and perfected as far as possible if maximum system performance is desired. This is of
particular importance to the downsized, modern, turbocharged three-cylinder engines now
found in many commuter vehicles. The fewer amount of cylinders means that the exhaust gas
pulses flowing through the turbine and the wastegate of the turbocharger are further apart (in
terms of time). This time increase allows the effects of any flow irregularities/imperfections
to be amplified, and as turbine control directly relates to compressor control and power
production, the controllability and predictability of the engine package, as a whole, is
reduced.

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1.2 What are the aims of the project?
The main aims of this project are; to develop some recommendations for
improvement to the design of a standard, flapper-door style, internal wastegate system, and;
to develop a greater understanding of the challenges facing wastegate system design.
For the outcome of the project, it is hoped that a simulation model of a turbocharger
with an optimised wastegate valve system (based upon the factory standard design with basic
modifications) will be created. This will come about through an evolution of CAD concept
ideas created in Solidworks, transferred in to CFD-ready flow domains to be analysed in the
ANSYS CFD software package. Each model will be analysed in detail to scrutinise its
performance and find an optimum valve and valve seat profile.

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2. Boost Control
Within limits, the more boost a turbocharger makes, the more boost it can make. Centrifugal
compressor air delivery increases exponentially with speed (to a point), and most are now
sized such that their maximum airflow capacity is vastly greater than the normal-charged
capacity of the engine being turbocharged (Hartman, 2007). The theory and anatomy of
turbochargers (Figure 1) was covered extensively in the part A report of this study (Cumner,
2014).
Figure 1: A typical modern turbocharger, the Garrett GT1544. (Zhejiang Rongfa Motor Engine Co., Ltd., unknown)
In order to control the feedback cycle of more exhaust energy making more turbo boost,
making more exhaust, making more boost, and so on until something breaks, it is critical to
interrupt the flow of exhaust energy entering the turbine - or the flow of boosted charge air
entering the engine - before things get completely out of hand. Hartman (2007) suggests that
overboosting has little adverse consequence on diesel engines, which easily tolerate very
large air surpluses that don’t make any power but help keep combustion cool. Turbocharged
spark-ignition engines, however, must have a boost control strategy.
As the name suggests, boost control is the term used to describe the method or strategy
implemented to control the boost pressure of a turbocharger system. The most common type
of boost control is some form of exhaust wastegate; a valve to divert exhaust gases away
from the turbine. However, there are systems that can control boost pressure from the inlet
side of the system, such as inlet vent valves – it should be noted that these inlet-based boost
control methods are rare in everyday turbo applications (Bell, 2002).

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2.1 Why Is Boost Control Needed?
There are several reasons why turbocharger boost pressure needs to be limited. According to
Bell (2002), the prime reasons are to prevent detonation (also known as knocking, pre-
ignition or pinging/pinking) and to preserve the condition of potentially delicate turbocharger
components, such as ceramic turbine wheels. In a similar vein of excess force being
transferred through components, boost control might be for the sake of transmission
component reliability, to avoid clutch slip or excessive gear wear, for example (Figure 2).
Another good reason to control boost is for the purpose of traction control (Bell, 2002). With
very high boost, torque levels at the driving wheels can be so excessive as to make control of
wheelspin impossible, particularly in lower gears on wet and greasy roads. Limiting boost in
such circumstances makes for safer and more rapid forward movement. Another reason for
boost control is to keep the turbo compressor working at maximum efficiency to prevent
undue heating of the inlet air charge (Miller, 2008). In terms of a compressor performance
map, this would be when a turbocharger is operating outside of its peak efficiency islands.
Heat in the inlet charge reduces engine power and can induce detonation; a cooler air charge
will allow more ignition advance, with additional power, driveability and economy benefits.
2.2 Boost Control Strategies
As discussed by Hartman (2007), turbocharged engines are typically designed with a
combination of constraints that become operative to control boost under various conditions -
these controls may be active or passive, intentional or unintentional. Modern dynamic boost
controls on factory produced vehicles are usually under electronic control, with highly
sophisticated logic regulating allowable boost, according to a complex variety of engine,
transmission, and environmental sensors. Boost control strategies vary widely in terms of
Figure 2: Loss of traction and damaged drivetrain components – two important reasons for the existence of boost
control. (The Art Mad, unknown) (unknown, unknown)

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their influence on power, torque, fuel economy, volumetric and thermal efficiency, turbo
longevity, and so forth.
In general, boost control strategies fall in to two overall categories: Cold-side and Hot-side
controls (respectively corresponding to the blue and red areas in Figure 3 below).
 Cold-side controls physically limit the amount of charge air that can flow from the
compressor in to the engine, usually by installing pressure-relief valves or introducing
dynamic or fixed bottlenecks in to the cold-side plumbing.
 Hot-side controls govern the speed and flow of the compressor by limiting the amount
of hot-side exhaust gas that makes it from the engine into the turbine, usually by
“wasting” a proportion of exhaust under certain conditions so that it bypasses the
turbine entirely.
Beyond the issue of cold versus hot-side, boost controls can also either be
Fixed/Geometrically based, or Dynamic/Active.
2.2.1 Fixed or Geometrical Boost Control
Structural charge-air or exhaust constraints can, by themselves, be intentionally calibrated to
limit boost by using smaller than optimal plumbing or restrictor-plate-type orifices installed
within the plumbing. However, such methods of boost control are not common on typical
modern automotive powertrains, since inlet restrictions tend to reduce the thermal efficiency
of the compressor by causing it to build excessive (hot) boost upstream of the restrictor that
will never be seen at the intake manifold. Restrictors on either side will also degrade engine
Figure 3: Turbocharger operational diagram (MazdaRotary, unknown)

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and turbo responsiveness, which is critical to good on-road feel and performance (Hartman,
2007). These fixed controls are typically seen on motorsport applications, where restrictors
can be mandatory due to specific race series regulations.
2.2.2 Dynamic Boost Control
As discussed by Hartman (2007), there are supplementary reasons to use dynamic (also
referred to as ‘active’) boost controls, other than just for higher power outputs. Beyond this
primary issue of performance, dynamic boost controls also protect the turbocharger by
allowing it to run closer to its operational limits without the risk of over-speeding, which
could cause major damage. Another advantage to more advanced modern dynamic controls is
that they can allow peak boost to vary dynamically, depending on a variety of circumstances,
which can protect various components from damage whilst pushing performance limits even
further. For a variety of reasons, virtually all automotive engines in production today use
dynamic boost controls.
By far the most common dynamic boost control device on modern turbocharged engines is
the exhaust wastegate valve; the wastegate controls turbine speed by diverting (‘wasting’)
exhaust around the turbine when intake manifold pressure (or occasionally exhaust manifold
pressure) exceeds a target value. Another dynamic turbine control strategy is the ‘variable
area turbine nozzle’ (VATN), which constantly sends 100 percent of the exhaust through the
turbine, but varies the exhaust energy applied to the turbine wheel by dynamically changing
the size of the turbine nozzle in order to calibrate the speed of the exhaust gases.
Given a particular engine size, pumping efficiency, and compressor pumping capacity, if
exhaust energy is not being bled off through a wastegate, maximum turbine energy will
ultimately be limited by the combination of exhaust energy, turbine nozzle size, and other
structural gas-flow constraints. Exhaust gas temperature – a critical component of exhaust
energy – is obviously also affected by factors such as the engine’s tuning parameters and heat
loss from the exhaust system upstream of the turbine.
Hartman (2007) highlights the point that dynamic controls can also be employed on the cold
side of the system. These include throttle-type butterflies that can close to restrict airflow,
drive-by-wire throttles that change position under computer control (even when the driver’s
floor stays fixed), and large wastegate-type devices that can open to bleed off boost air before
it enters the intake manifold.

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2.2.3 Cold-side Boost Controls
2.2.3.1 Compressor Flow Capacity
Any compressor will eventually begin running out of air-flow capacity if run fast enough,
which will limit further increases in boost pressure. This is known as ‘choke flow’ – when the
mass-flow-rate limit of the compressor is reached; this is represented graphically in Figure 4.
Hartman (2007) articulates that one would not normally want the compressor running near
the upper limits of its performance envelope, as thermal efficiency will be at its worst in this
region. This theory is supported by the research undertaken by the author in part A of this
project; hence it can be seen that relying on flow capacity alone is a simple but poor method
of overall boost control.
Figure 4: Compressor flow map showing the defined limits of a compressors flow capability (Garrett, 2015)

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2.2.3.2 Blow-Off/Pressure-Relief Valves
Figure 5: Diagram of blow-off valve. When pressure limit is reached, valve opens (shown on right). (GReddy, 2015)
Virtually all modern automotive turbo engines are equipped with a blow-off valve (Figure 5)
to increase the life of the turbocharger by limiting surge forces against the compressor and
bearings from sudden throttle closure, which produces instant high manifold vacuum
downstream of the throttle and a spike of high overpressure upstream of the throttle.
A blow-off valve is not directly actuated by boost pressure pushing against the valve, which
could only be used to relieve surge pressure above that of normal boost. Instead, when the
throttle closes, high manifold vacuum against the blow-off valve actuator immediately opens
the pop-off valve and keeps it open until the next time the throttle opens. A small blow-off
valve will usually handle the job of dumping boost pressure trapped upstream of the throttle
since turbine energy and engine volumetric efficiency immediately decrease when the throttle
closes.
A common second type of pressure relief valve functions more like a radiator cap installed
upstream of the throttle body as a backup boost-control device should the wastegate fail
(which can happen easily if the wastegate manifold vacuum reference line is severed or
kinked). Excessively high manifold pressure overcomes spring pressure in the valve to
prevent extreme overboost.
Larger spring-loaded pressure-relief valves are sometimes used as an ordinary boost-control
device by venting large amounts of excessive pressure from the intake tract. This third type of
blow-off valve has also been used by some sanctioning bodies in the past to limit turbo boost

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on race cars (Hartman, 2007). Disadvantages include the fact that this type of boost control is
prone to ‘flutter’ if not properly damped, producing a loud noise that some drivers may find
irritating. Under certain conditions, a big enough compressor will overboost the engine even
with the blow-off valve wide open – a strategy which race teams used in the past to break the
rules with impunity when sanctioning bodies required a standard-issue blow-off valve instead
of a restrictor orifice in the inlet. As this method of boost control does not actually limit
turbine speed, there is nothing intrinsic in the design that prevents the turbocharger from
accelerating out of the high-efficiency range of the compressor with the blow-off valve wide
open.
2.2.3.3 Actuated Inlet Butterflies
Figure 6: A typical butterfly valve to control air-flow in an engine (unknown, 2006)
A rotating, actuator-controlled, choke or throttle plate (typically seen in the form of a
butterfly valve, as in Figure 6) installed in the compressor inlet plumbing, managed according
to feedback from a manifold-pressure reference line connected to the intake manifold, will
limit boost. However, there is nothing to keep turbocharger speed from increasing into less
efficient regions of the compressors operating envelope, which will raise the intake air
temperature at maximum boost - exactly when the detonation-inducing effect of hotter charge
air is wanted least. (Hartman, 2007)
Unfortunately, any inlet restriction upstream of the compressor inlet also increases the
likelihood of compressor surge by increasing the pressure differential between the
compressor inlet and discharge.

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2.2.3.4 Intake Plumbing Restrictor Plates
As documented by Hartman (2007), these have the same disadvantages as inlet butterflies,
only they are permanent; an air cleaner or air intake that’s too small can also effectively
function as a restrictor plate. Restrictive or undersized throttle bodies or carburettors will also
limit boost under some circumstances, but such restrictions are more likely to simply degrade
the thermal efficiency of the turbocharger by forcing it to work harder. Unfortunately, people
often unintentionally and unknowingly ‘acquire’ both these types of ‘boost control devices’
when they modify a factory turbocharged engine by overboosting the stock turbo system
without removing resulting bottlenecks.
As mentioned previously, intake restrictor plates, such as that attached to the turbocharger in
Figure 7 below, are rarely found outside of motorsport, where they are used to limit power or
‘even the playing field’ between different cars and engines.
Figure 7: An intake restrictor, decreasing the intake diameter of a turbocharger compressor inducer. (Force-D Rally
Team, 2012)
2.2.3.5 Drive-By-Wire Throttle
Turbocharged engines with drive-by-wire (DBW) throttles have access to the same ultimate
method of boost control available to the driver: reducing throttle input. An obvious drawback
to this type of boost control is that some combinations of engine and turbine speed will not be
reachable. Another is that closing the throttle suddenly whilst operating at high boost reduces
the volumetric efficiency of the engine and results in higher exhaust backpressure. This is
because some extra turbine power is required to force boosted air charge into the engine, past
the throttle that would not be required if the throttle could be farther open at that time.

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Essentially, installing or tolerating otherwise needlessly restrictive inlet plumbing requires
the turbocharger to work harder, which makes the engine less efficient. From a technical
point of view, it is always preferable to control boost from the ‘hot side’.
2.2.4 Hot-side Boost Controls
2.2.4.1 Backpressure
Excessive, or limited, backpressure on either side of an exhaust turbine can be detrimental to
the performance of a turbo engine; however, restrictive manifolds, mufflers, catalytic
converters, and exhaust piping can be employed intentionally to control boost. The 1960s-
vintage Chevrolet Corvair Turbo had no active boost controls; the Corvair Turbo depended
entirely on structural constraints in the exhaust system to prevent overboost on this primitive
carburetted turbo engine (Miller, 2008). However, the exhaust system has also
unintentionally become a boost-control device, of a sort, on many modern overboosted
factory turbo engines, limiting either the rate of compressor spool or the maximum boost
pressure. Hartman, 2007, states that comparing intake and exhaust manifold pressure can be
an eye-opening experience for many engine tuners and technicians, who discover that exhaust
pressure can be several times that of boost pressure.
Figure 8: Diagrams depicting theoretical effects of exhaust piping being too small (top), correctly sized (bottom left),
and too big (bottom right). Each white area represents an exhaust gas pulse. (Team Integra, 2002)

12
It is also worth noting that simply dumping turbine discharge out of a short, wide pipe into
the atmosphere can sometimes decrease the performance of a turbo engine, by removing the
beneficial scavenging effect of fast-moving exhaust gases moving away from the turbine
discharge in a long pipe or muffler. The exhaust system can greatly affect the swirl and
turbulence of exhaust gases exiting the turbine, with significant performance effects. Figure 8
(on previous page) shows, in a simplified manner, how exhaust piping size can affect exhaust
gas flow in an internal combustion engine.
2.2.4.2 VATN/VGT/VNT Turbines
Figure 9: Diagrams of a VNT Turbocharger, as part of a Volvo 5-cylinder diesel powertrain. (Volvo, 2010)
From a performance and efficiency point of view, the optimal method of managing boost is to
control turbocharger speed via the turbine wheel, with a variable area turbine nozzle (VATN)
turbocharger, also known as a variable-geometry turbine (VGT) or Variable Nozzle Turbine
(VNT) turbo. Whatever the chosen name, this type of turbocharger (shown in Figure 9)
dynamically alters exhaust energy by changing the exhaust speed and flow path on its way
into the turbine wheel.
In a VATN turbine, all exhaust gas flows through the turbine wheel at all times, keeping the
turbine and housing fully heated. A circle of adjustable vanes arranged around the turbine

13
wheel rotate dynamically in concert to narrow or widen the effective size of the turbine
nozzle; this is done to manage turbine energy and provide very fast spooling with safe peak
boost. Typically, a spring-loaded pneumatic actuator, referenced to intake or exhaust
manifold pressure, rotates a disc that simultaneously changes the position of all the vanes.
VATN turbochargers are becoming more common in modern road vehicle engines (Bell,
2002), but there are downsides. The turbine housing is an extremely hostile environment for
the small moving parts of a VATN mechanism, which must survive extreme heat, large
temperature changes at engine startup and coming off idle, and the corrosive effect of various
exhaust gases, liquids, and solids, including water and waterborne acids. Early VATN
systems had various reliability issues due to their complexity, and with more components
they are evidently more expensive to manufacture. With increased applications of VATN
turbos in modern powertrain systems, the impact of both of these aforementioned concerns is
becoming less of an issue.
2.2.5 Wastegates
Hartman, 2007, comments that wastegates are “…overwhelmingly the method used to control
boost on modern turbo engines.” A wastegate is essentially an actuated high-temperature
valve – typically a poppet, butterfly, or flapper – installed in the exhaust system upstream of
the turbine wheel that regulates exhaust energy by opening to allow a variable portion of the
exhaust gas to bypass the turbine entirely.
The wastegate valve is usually held closed by a strong spring. As a safety measure, the valve
should be designed such that exhaust backpressure tends to help push the valve open rather
than helping the spring to hold it closed. The wastegate is not normally opened by exhaust
pressure pushing against the valve (though this may happen if backpressure gets high enough
in the exhaust system), but typically by manifold pressure pushing against a large control
diaphragm that has the power, through mechanical advantage, to move a spring-loaded rod
which in turn can over-come the wastegate spring force to open the wastegate.
As discussed briefly in Part A of this study (Cumner, 2014), there are two overall forms of
wastegate; integral and non-integral - also known as internal and external. Integral (internal)
wastegates are built in to the design of the turbo, and as such have the outlet for the excess
boost/exhaust gas built in to the turbine housing. Non-integral (external) wastegates sit

14
separate from the turbo and can be affixed wherever appropriate further downstream in the
exhaust system.
Figure 10: View of a typical internal wastegate setup, looking at the mounting flange face with turbine exducer (left)
and wastegate system (right). (Sonic Performance, unknown)
Internal wastegates, such as the setup seen in Figure 10, are typically designed around a
flapper door style valve that opens to uncover a port capable of allowing exhaust gases to
escape the turbine inlet scroll upstream of the turbine wheel, thus bypassing the wheel. The
flapper is typically opened or closed by a sealed shaft welded to a small crank lever located
on the exterior of the turbocharger. This crank is actuated by the control rod of a spring
loaded diaphragm located on the cold-side of the turbo, which is generally referenced to
either: intake manifold pressure; compressor discharge pressure; exhaust manifold pressure;
or a pulse-width-modulated (PWM) valve referenced from one or more pressure sources.
This type of actuator diaphragm is usually manufactured in such a way that the canister is
sealed, and the spring and diaphragm are inaccessible without destroying the canister
(Hartman, 2007). The typical internal wastegate’s ‘flapper door’ valve is normally located
next to the turbine discharge at the outlet face of the turbine housing, which is designed so
that a single auxiliary housing bolts to the exterior of the main housing to collect exhaust
from both the turbine exducer and the wastegate port (when open). It is the design of this
valve and its seat that will be investigated in depth, later in this report.

15
Figure 11: Example of an external wastegate setup (bottom of image). (Radium Engineering, 2010)
External wastegates (Figure 11) normally consist of a flanged cast-iron or Inconel housing
containing a poppet valve or high-temperature butterfly attached to an actuator diaphragm
located in a serviceable housing along with a removable strong spring that can be swapped to
alter the maximum allowable boost level. When the wastegate opens, exhaust flows past the
valve and along a passage in the housing to a flanged discharge port or spout. From the
wastegate discharge, ‘wasted’ exhaust may be routed back in to the main exhaust flow
downstream of the turbine discharge or into an independent tailpipe or muffler.
The wastegate is an important feature in current turbo systems due to the wide RPM range of
modern automotive engines (Miller, 2008). In comparison to older turbochargers, Miller
explains how the modern wastegate allows powertrain engineers to use smaller and more
responsive turbines, thereby increasing torque at lower engine speeds and minimizing
turbocharger boost lag. In the absence of a wastegate, this smaller turbine housing would
restrict exhaust gas flow, cause too much exhaust back pressure, and therefore create
excessive engine pumping losses. A pumping loss essentially represents a loss of engine
power that is used to move gases in and out of the cylinders. As discussed earlier, while
exhaust back pressure is absolutely necessary to actually drive the turbocharger turbine,
which in-turn drives the compressor, there is also such a thing as too much back pressure.

16
Miller (2008), states that if an existing factory turbocharged engine (with an internally
wastegated turbocharger) is to have a significant power increase (typically beyond a 200%
increase) then an external wastegate would be required along with a non-internally
wastegated turbo; this is due to a phenomenon known as ‘boost creep’.
Garrett (Garrett (by Honeywell), 2015) describes boost creep as a condition of rising boost
levels past what the predetermined level has been set at. Boost creep is caused by a fully
opened wastegate not being able to flow enough exhaust to bypass the housing via the
wastegate itself. For example, if an engine’s maximum boost level is set to 12psi, and the
engine goes in to full boost, readings of 12-13psi would normally be seen quite quickly.
However, if the turbocharger is suffering from boost creep, the boost pressure will continue
to increase with RPM to perhaps 14-15psi – hence this phenomenon is more pronounced at
higher RPMs. Effective methods of avoiding or eliminating boost creep can include porting
the internal wastegate opening to allow more airflow out of the turbine, or to use an external
wastegate.
2.2.6. Wastegate Valve Control Strategies
There are various methods of physically actuating an exhaust wastegate, variable area turbine
nozzle, blow-off valve, or restrictor valve, all of which directly alter airflow or exhaust
energy flow through a turbocharging system. As discussed by Hartman (2007), these types of
control valves may be operated with:
 A manually controlled cable or rod (fairly common on older piston-engine aircraft)
 Pneumatic pressure from the intake or exhaust manifold acting against a diaphragm
and control rod.
 An oil-pressure-driven servo motor (essentially a hydraulic cylinder) that may be
controlled manually or according to airflow, air density, turbocharger speed, or
various other parameters.
On most modern turbocharged engines, the most common control-sensor strategy is to equip
the turbo system with a mechanical wastegate actuated by manifold “gauge” pressure.
Maximum allowable peak boost can be adjusted by swapping the spring in the wastegate
actuator to one with higher or lower pressure, or in some cases by changing the amount of
preload against the wastegate spring by adjusting the mechanical linkage.

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3. Premise of the Experiment
3.1 Why does it need improvement? – Part open control
The standard wastegate system consists of a flat faced, sharp edged valve seat and valve. The
author believes that this valve and valve seat geometry is not aerodynamically efficient and is
likely to flow badly at small-angle valve openings. This issue has likely not been addressed as
the majority of the time during normal operation the wastegate valve is either fully open or
fully closed; hence the flow capability of the valve at small-angle openings is not of any
concern.
Rather than focussing on outright flow capability, the aim of the following experiments is to
improve the quality of the flow through the valve, and in to the rest of the exhaust system.
Increasing the quality of the flow is about increasing the predictability and efficiency of the
flow, to allow more precise control of the wastegate in advanced, modern powertrains.
Wastegate control may become a more useable, important control system in future engines, if
the wastegate flow characteristics can be predicted more accurately.
Bell, 2002, covers the topic of wastegate flow problems, where he states that wastegate flow
and turbine exducer flow should run parallel to one another, in two laminar flow streams –
this feature shall be one of the main aims of the later experimentation models.

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4. Simulation Model Creation and Setup
To investigate the effects of changing the design of the wastegate valve system, a specific
turbocharger was required so that real measurements could be taken and the components
modelled accurately. The internal wastegate system of the Garrett GT1544 turbocharger was
chosen as the model subject for this investigation. This turbocharger was chosen in Part A of
this study, ‘Turbocharging a Four Stroke, Four Cylinder Petrol Engine’ (Cumner, 2014), as
the optimal turbocharger for doubling the horsepower of a 1275cc Classic Mini engine.
The first step towards making any recommendations for improvement to the wastegate design
was to analyse the architecture and performance of the standard wastegate valve and valve
seat of the GT1544 turbo. After this, revised valve and valve seat designs could be
conceptualised, modelled and performance analysed.
4.1 CAD geometry (Solidworks)
To begin the analysis of the standard wastegate valve, the first task was to model the relevant
area of the turbocharger; there would be no need to model the entire turbo when only
focussing on the wastegate design. The required components encompassed the following: the
turbine housing (Figure 12), the wastegate valve, wastegate valve arm and mounting pin (all
can be seen in Figure 13), and some form of down pipe to give the exhaust gases somewhere
to flow in to. Figure 14 shows the wastegate valve opened past its operational maximum and
in relation to the turbine housing inlet – this gives an idea to the flow path of the wastegate
gases.
Figure 12: Turbine housing, viewed from the exducer side with wastegate at top centre of image

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Figure 13: The wastegate valve (disconnected from its external pressure actuator) opened to two arbitrary angles
Figure 14: Photograph showing relation to turbine housing inlet (right) and wastegate port (middle) with wastegate
valve swung all the way round for clarity
Engineering drawings were used, alongside a real turbo (shown in the figures above - this
unit was purchased for a low price due to a shaft bearing failure), to develop an accurate
representation of the wastegate system - along with a simplified representation of the turbine
outlet (also known as the turbine exducer) in the form of a simple circular opening. The
turbine outlet was modelled to study the interaction of the two exhaust gas flows from the
wastegate and turbine. As they both enter in to the same shared volume, in to the exhaust
down pipe, a degree of interaction is expected between the gas flows. The actual turbine
wheel was not modelled, as this would have been an unnecessary and lengthy process. All
CAD modelling in this study was performed on Solidworks.
The model began with the creation of the mating flange profile of the outlet side of the
turbine housing, created using an accurately dimensioned engineering drawing from Garrett,
the turbocharger’s manufacturer. This flange profile was slightly different to the purchased

20
turbocharger used for further reference, but the overall dimensions and main reference points
were identical. The outline steps of the process of modelling this flange profile are shown in
the following figures.
Figure 15: Creation and positioning of the main reference circles for the flange profile
Figure 15 above shows the first geometry points being created, with the outer mounting bolt
holes and the centroid of the turbine exducer creating the initial references for the rest of the
profile. This Solidworks sketch was drawn on the side of a 3D extruded block, created to
mimic the overall outer dimensions of the complex turbine housing casting. The reference
drawings on the right-hand side of Figure 15 (and subsequent Figures) can be seen in full in
Appendix A at the end of this report.
Figure 16: Further reference points added to sketch

21
Figure 16 (on previous page) shows the next development of the profile sketch, with the outer
profile of the flange beginning to take shape. From here, numerous straight edges and radii
were introduced and the profile cleaned up to create the final image, shown below in Figure
17.
Figure 17: The final flange profile sketch, a complex amalgamation of profiles to match the engineering drawing
This flange profile sketch was extruded from the main block by a depth measured, in person,
from the reference turbocharger.
The turbine housing inlet (which intakes the exhaust gases from the cylinder head exhaust
port outlets via the exhaust manifold) was then modelled, situated in the correct location
relative to the main outlet mounting flange, shown in Figure 18 – the exact positioning was
determined from the engineering drawings in Appendix A.
Figure 18: The turbine inlet was modelled, seen in context on the left and in profile on the right

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A lofted cut along an approximate air path between the turbine inlet and the wastegate valve
was produced to simulate the flow path of the wastegate gases (Figure 19). This was done to
avoid having to model the complex, decreasing volume, spiral profile of the entire turbine
housing, as this was not necessary to study the effects of changing the wastegate valve design
and would have added unnecessary time to the modelling process.
Figure 19: Lofted cut path sketched in to top of block (left), and trying to capture the created cut flow path (right)
A circle was created within the flange profile, and extruded-cut through the entire base block.
This simple, straight path would represent the turbine exducer flow in the CFD models. This
simulated turbine flow path can be seen in Figure 20 below, compared to an image of a real
GT1544 turbocharger.
Figure 20: Completed turbine housing, without the wastegate valve. Solidworks model (left), reference image (right)
(Engine Basics, 2010).

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The actual wastegate valve was then modelled (shown in Figure 21), to match the dimensions
of the real valve. The valve looks deeper/taller than the real-life counterpart shown earlier in
Figure 13, because of some disparity between the engineering drawings and the slightly
different version of GT1544 turbo that was purchased for further reference purposes. This
does not affect the function of the valve or the validity of the later CFD models.
Figure 21: Solidworks model of factory wastegate valve
Along with the valve itself, the wastegate valve actuator arm and the rivet/pin that holds the
valve to the arm was modelled and the entire assembly then mated as per the real system. The
arm (minus the pin and valve) is shown in place below in Figure 22.
Figure 22: Valve arm in place in turbine housing, with construction lines to check centralisation of mounting pin hole
This assembly allowed the valve to function exactly like the real system, to be opened to
correct, realistic angles as the valve moves along the arc determined by the geometry of the
valve arm and its hinge position. This principle is a key factor in the reasoning to improve the
flow of the valve, due to the curved opening path giving rise to asymmetric cross-sectional

24
area. Developing an accurate and realistically mated Solidworks assembly allowed the
creation of CFD-ready models with the valve hinged open to a user-defined amount of
degrees (specified by the “hinge mate” shown below in Figure 23). Note that the actual valve
arm could not be included in the later CFD models due to an unfortunate zero-thickness error,
but the presence of the arm was not necessary to study the flow characteristic of the valve
itself.
Figure 23: Details and images of the hinge mate used to control the wastegate valve opening angle (set to 20 degrees
here)
Figure 24 below shows the factory valve set to an opening angle of 10 degrees, viewed from
the side through a translucent turbine housing.
Figure 24: Side view of factory valve open to 10 degrees. Turbine housing set to translucent.
After the factory wastegate valve was modelled, several alternative concepts were developed,
from rudimentary sketches in to Solidworks models integrated in to the entire turbocharger

25
assembly. A valuable feature of modelling the valve assembly like the real system is that the
geometry of the valve concepts could be tested to see if they would physically work within
the factory turbine housing. The design of the valves took several attempts to make them
work (through some trial and error) and fit them within the standard geometry of the
wastegate port through the full range of opening angles.
The original basic concept sketches are shown below in Figure 25 – all were based on the
theory of smoothing or redirecting the gas flow path of the wastegate to create a more
predictable flow at small valve openings. Note that the idea of altering the valve seat profile
is explored later in this study in Chapter 7.
Figure 25: Original pen and paper sketches for altered valve designs
From these basic sketches, 3D CAD models were produced in Solidworks and then placed in
to relevant assemblies with the factory turbine housing. The aim was to make sure the
original turbine housing could be used without modification, hence the concept valves
needing to work with the original housing geometry. The following figures show the valves
from the side opened to 10 degrees, again seen through a translucent turbine housing. The
concept valves in the figures are as follows:
 Hemi-spherical valve (Figure 26)
 Cone valve (Figure 27)
 Concave cone valve (Figure 27)
 Wedge valve (Figure 28)
 Pyramid wedge valve (Figure 29)
Figure 26 shows the hemi-spherical design, which was theorised to smooth out the gas flow
direction change, along with attempting to even out the cross-sectional asymmetry from one
side of the valve to the other. The areas circled in red show a much more even cross-sectional

26
area available for exhaust gases to flow through, when compared to the factory valve (Figure
24). The downside to this is that the flow area is reduced, which may seem like an immediate
reason for rejecting this valve – remember, however, that the idea behind this modification is
not to increase flow capacity, but to improve flow quality. This concept can be seen in the
majority of the subsequent valve design concepts.
Figure 26: Hemi-spherical valve.
Figure 27 shows two cone-based valve designs, which are expected to begin redirecting the
flow at an earlier stage than the hemisphere valve.
Figure 27: Cone valve (left) and concave cone valve (right).
Figure 28 shows a wedge valve, designed to split the gas flow through the valve in to two
distinct directions. This valve was modelled in the orientation shown below, and also rotated
through 90 degrees to study the effects of biasing the wastegate flow towards the upper/lower
faces of the downpipe, and then to the left wall and to the turbine exducer flow stream to the
right, respectively.

27
Figure 28: Wedge valve, shown in two different views for clarity.
The pyramid wedge valve shown below in Figure 29 is noticeably taller than the wedge valve
above, simply due to the geometric constraints of the swinging-style valve actuation method.
Figure 29: Pyramid wedge valve, shown in two different views for clarity.
A simple ‘down pipe’ was added to each turbine assembly, to give the gases somewhere to
flow in to. Modelling of a more realistic, 90 degree-bend down pipe was attempted, however
during a test run the geometry within the pipe caused several unsolvable errors during the
meshing process in ANSYS; hence a simple open volume was created instead.
The finished model assemblies were each placed inside a ‘mould block’ and CFD flow
domains were formed from ‘cavities’ created in the mould block using the cavity tool in
Solidworks. This process essentially created ‘negative images’ of the turbine housing models
created in Solidworks - these domain models represented the regions in which gas could flow
through the wastegate, turbine outlet, and down pipe These negatives were required due to
the CFD software, ANSYS, requiring solid material for mesh generation and fluid flow
simulations (ANSYS cannot mesh empty space). A model inside the mould block can be seen
in Figure 30, with just the simplified downpipe set to be opaque for clarity.

28
Figure 30: Turbine housing assembly inside the 'mould block'
Figure 31: Wireframe model of a completed CFD domain.
Figure 31 shows a transparent wireframe image of a completed CFD domain, after some
superfluous excess material had been trimmed from the outer edges. Essentially, the open
volume and solid material of the original CAD model were swapped around; therefore the
wastegate valve was now represented by empty space and the flow regions represented by
solid material.
The opening angle of each wastegate valve model was set to 10 and 20 degrees (where 0
degrees is fully closed) and a CFD domain made for each. This resulted in the creation of 14
initial domains: 2 of each 6 valves (10 and 20 degrees); a factory with closed valve; and a 90-
degree rotated wedge at 20 degrees open. The factory standard setup was analysed first, via
the use of the CFD software package ‘ANSYS’, as described in the next section.

29
4.2 CFD Simulation (ANSYS)
The following describes the procedure for all simulation models. Within ANSYS workbench,
a ‘Fluid Flow (CFX)’ system was selected, and the relevant domain geometry imported in the
form of a Solidworks part file. The mesh settings were left at defaults, with three named
selections being chosen to represent the inlets and outlets: InWaste, InTurbine, and Outlet.
The mesh was then generated and the setup module was entered.
4.2.1 CFX-Pre: Setup/Determining the Flow Parameters
In order to simulate the flow of exhaust gases through the turbine housing of a turbocharger,
several parameters must be known about the gas and its flow features. There are several
factors by which the flow motion can be determined, and it was initially decided that the
gauge pressures of the wastegate tract and the turbine exducer would be used to determine the
motion of flow. These pressures were deduced (approximately) as shown below:
Pressures
 Pressure in exhaust manifold (before turbine) ~ 2.5x the inlet boost pressure
(MaxBoost, unknown)
 Maximum inlet boost pressure in this application is 16psi, determined in Part A of this
study (Cumner, 2014)
 Wastegate creep means the valve will be open around 10 degrees at approximately
60% of pressure limit (MaxBoost, unknown) so at (16*0.6=) 9.6psi.
 (9.6*2.5=) 24psi. This is the approximate calculated back pressure in exhaust
manifold (wastegate pressure).
 Hence, the pressure in the system before the turbine, relative to atmosphere = 24psi =
1.655 MPa
 Pressure after turbine (i.e. at the turbine exducer) = 1.415MPa (EasyCalculation,
unknown)
Temperature = 1000C through wastegate, mixing with 850C gas from turbine exducer.
(Banks Power, 2014)
The pressure and temperature of the gas should have, in theory, been all that was required to
model the flow of exhaust gases through the turbine housing. However, when an initial test
run was performed, it was found that the fluid would simply not flow through the domain,
instead stagnating and reversing direction, with gases from the wastegate valve turning round

30
and going backwards through the turbine exducer. The simulation would always fail
prematurely and produce a large amount of error messages. For this application, something
was fundamentally wrong with using pressure as the driving force for the motion of the fluid,
so instead of wasting time troubleshooting the issue, the decision was made to use flow
velocities in place of pressures; this ensured the gas would flow in a more predictable manner
and give much more useable results. The calculations for exhaust gas speed were as follows:
Gas speed
 1.3 litre engine at 3000rpm (approx. rpm to generate 9.6psi)
 3000rpm = 50rps = full exhaust gas expulsion on only half of those revolutions, hence
1.3 litres of gas 25 times per second, which equals 32.5 litres per second.
 Length of exhaust pipe required to hold 1 litre of gas = 1,000/25.7 = 38.91cm
 Hence, the exhaust would flow 38.91cm/s if it were displacing 1 litre of gas.
 To displace 32.5 litres/sec (32.5 times the volume), v = 32.5*0.3891 = 12.45m/s
Wastegate gas flow speed = 12.45m/s
Turbine gas flow speed = 0.8*12.45 = 10m/s (Bell, 2002)
The default, ANSYS library provided, “Air at 25°C” was used as the gas for all flow
simulations. Whilst the much hotter exhaust gas flowing through a turbocharger turbine
would have different properties to normal, ambient temperature air, the chemical make-up
would still consist of a majority of Nitrogen gas (NGK, unknown). The chemical composition
was not important to compare the flow characteristics of the valves, plus the time taken to set
up each model with a custom gas would have added a lot of time to the overall process.
Figure 32: Wastegate flow parameters (left), turbine flow parameters (right)

31
The parameters for the wastegate and turbine flow boundaries, used in all subsequent models,
are shown in Figure 32 on the previous page. The box on the left shows the parameters used
for the wastegate flow (InWaste) - note the higher flow velocity and higher temperature, due
to the flow not being impeded by the turbine wheel and the gas not being decompressed and
having some thermal energy removed to power the turbine. The box on the right shows the
parameters used for the turbine exducer flow (InTurbine), with the slower flow velocity and
lower temperature. The ‘Outlet’ boundary was simply set to have 0Pa reference pressure, so
the gas streams could flow in to and through the down pipe volume with an effective ‘net’
zero exhaust back pressure (the optimum flow condition, as shown earlier in Figure 8). These
flow boundaries are shown below in Figure 33.
Figure 33: Flow boundaries on the turbine housing domain
4.2.2 CFX-Solver: Obtaining the Solution
Obtaining the solution was simply a case of opening CFX-Solver and requesting that the
solution be found. However, whilst the simulations were running to determine the solution,
the message shown in Figure 34 was seen quite regularly. This message means that some of
the gas flow attempted to reverse direction and return in to the domain the wrong way
through the outlet – likely an unfortunate consequence of having a non-convergent,
simplified down-pipe.

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Figure 34: CFX-Solver notice message indicating flow reversal
4.2.3 CFD-Post: Viewing the results
Four main visualisations were chosen for comparative analysis – the turbine exducer flow
streamlines, wastegate flow streamlines, and overall temperature and pressure surface plots.
The velocity streamlines were created from 50 seed points, as this was dense enough to give a
clear image of what the flow was doing in the domains, but not so dense that one could not
see clearly through the streamlines.
When discussing the results in the following chapters, the following diagram in Figure 35
gives reference to the terms used in describing features of the gas flows. (left, right, upper
wall, lower wall, wastegate valve area, turbine exducer, outlet)
Figure 35: Diagram showing model orientation references

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5. Analysing the Factory System
5.1 Factory Turbo with Wastegate Closed
This first model (Figure 36) was created to be able to view the flow out of the turbine exducer
exclusively, with no flow out of the wastegate valve to interfere with this primary flow path.
This simulates lower-rpm running conditions where the engine has not yet built up enough
inlet-side compressor boost to warrant opening the wastegate valve on the exhaust side to halt
the production of further boost.
This first model gave a useful comparison point to further flow simulations, so that the flow
interaction characteristics of different valves could be evaluated, not only against the other
valve concepts, but against the conditions of zero wastegate flow.
In a real turbocharger, the exhaust gas flow would simply bypass the wastegate valve tract if
the valve were closed, but in this basic model the flow through the simulated, approximated,
wastegate flow path (seen in Figure 37) was simply not modelled.
Figure 36: Solidworks model of factory turbo setup with wastegate closed
Figure 37: Side view of the closed factory wastegate valve, viewed through a translucent turbine housing

34
The velocity streamlines shown above in Figure 38 indicate that there was a small amount of
gas recirculation within the downpipe volume, and that gas flow velocity stayed high in the
central portion of the flow stream. The large portion of empty space directly out of the
turbine exducer caused the flow path to deviate leftwards (in the orientation context of this
model), due to low relative pressure in this region with zero wastegate flow.
The pressure contour plot shown below in Figure 39 also supports this observation, by
showing that the area of lowest pressure was in front of the wastegate valve outlet. The area
of highest pressure being on the far left upper corner of the outlet (when compared to the
turbine exducer location) also shows that flow was biased towards this edge/corner of the
domain. This issue would likely be much less prevalent in a real application, due to spatial
packaging constraints; an exhaust down pipe would likely force the turbine exducer flow path
around a sharp corner shortly after the mounting flange, not giving the gas flow sufficient
distance to curve towards a low pressure volume of non-moving air to the side.
Figure 38: Velocity streamlines of turbine exducer (factory valve closed)
Figure 39: Pressure contour plot (factory valve closed)

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5.2 Factory Turbo With Wastegate Valve Open Ten Degrees
As can be seen from comparing the closed wastegate valve model (Figure 38) to this ‘10
degrees open’ model, via the velocity streamline screenshots in Figure 40, the open wastegate
valve makes a noticeable difference to the turbine exducer flow path. The sudden influx of
wastegate flow towards the turbine exducer flow causes a large depression in the main flow
stream and even induces some premature flow reversal, as the exducer flow begins to curve
around the wastegate flow stream in a spiral fashion.
Figure 41 gives a vivid representation of the problems facing this wastegate valve system.
There is a large region of turbulence directly after the valve, and a very uneven distribution of
flow velocity from the top of the valve to the bottom. A more predictable flow profile would
be achieved through an even, laminar flow stream, something inherently difficult to achieve
with this style of wastegate valve actuation due to the awkward valve opening path and sharp,
sudden edges to the valve and its seat.
Figure 40: Velocity streamlines of turbine exducer (factory valve open 10 degrees)
Figure 41: Velocity streamlines of wastegate valve (factory valve open 10 degrees)

36
The distribution of temperature on the outer surface of the turbine housing can be seen in
Figure 42. This shows the effect of the hotter wastegate gases mixing with the decompressed,
cooler turbine exducer gases. The asymmetry of the wastegate flow is shown by the hottest
temperature profile extending along the top and bottom surfaces of the turbine housing
directly after the wastegate. The almost perpendicular direction change of the wastegate gases
also causes a slight temperature increase around the circumference of the turbine exducer.
The pressure contour plot shown in Figure 43 indicates a region of high pressure at the
bottom edge of the valve area, due to the majority of the flow being directed downwards. It is
curious to note that the region of lowest pressure is around the top edge of the valve seat area
– another consequence of the sudden change in flow direction (down) at the wastegate valve.
Figure 42: Temperature contour plot (factory valve open 10 degrees)
Figure 43: Pressure contour plot (factory valve open 10 degrees)

37
5.3 Factory Turbo With Wastegate Valve Open Twenty Degrees
Figure 44: Velocity streamlines of turbine exducer (factory valve open 20 degrees)
Comparing the streamlines of the 20 degree model in Figure 44 to those of the 10 degree
model in Figure 40, the flow from the turbine exducer is seen to be more disrupted by the
wastegate flow with a larger valve opening. The flow stream is pulled over to the wastegate
side of the downpipe sooner than before, with a larger amount of cross-flow and flow
reversal. The flow characteristics of the turbine exducer can therefore be said to worsen with
increasing wastegate valve opening angle.
The wastegate flow shown in Figure 45 correlates with the observations of the turbine
exducer flow. When compared to the streamlines from the 10 degree model in Figure 41 there
is noticeably more turbulence in this model, with a more developed flow vortex in-line with
the wastegate valve. There is also more flow separation from the lower downpipe wall, likely
caused by low pressure from the vortex. Another flow feature to note is a pocket of stagnated,
swirling gas below the valve, seen in the lower-right corner of the left image below.
Figure 45: Velocity streamlines of wastegate valve (factory valve open 20 degrees)

38
Figure 46: Temperature contour plot (factory valve open 20 degrees)
The increased valve opening causes the hottest portion of the temperature plot in Figure 46 to
extend further along the top and bottom surfaces of the turbine housing than in the 10 degree
model. The perpendicular direction change of the wastegate gases this time causes a larger
temperature increase around the circumference of the turbine exducer, indicating that more
heat transfer occurred between the gas and the containing walls of the downpipe at this
location.
The pressure contour plot shown in Figure 47 indicates a more even spread of pressure
around the valve seat than the 10 degree model. Again, the consequence of the extreme flow
direction change at the valve can be seen where a region of high pressure is located in a
narrow area directly in-line with the majority of the gas flow directed downwards from the
valve.
Figure 47: Pressure contour plots (factory valve open 20 degrees)

39
6. Analysing The Proposed Valve Designs
6.1 Hemisphere Valve
6.1.1 Ten Degrees Open (Hemisphere)
Figure 48: Velocity streamlines of turbine exducer (hemi valve open 10 degrees)
As seen in Figure 48, the turbine flow stream is more focused with the hemisphere valve; the
stream retains more of its original shape than the factory setup, perhaps even performing
slightly better than when the valve was closed, as in Figure 38. There is a very small amount
of flow separation from the main flow stream, but this is not a major issue.
Figure 49 shows the streamlines of the wastegate flow for the hemisphere valve. The main
feature here is the very prominent vortex, which, whilst complex, is actually only made of 2
or 3 inidividual streamlines (determined from playing a streamline animation video in CFD-
Post), showing a region of extreme flow recirculation. The lower face flow separation is
comparable to that of the factory valve.
Figure 49: Velocity streamlines of wastegate valve (hemi valve open 10 degrees)

40
Figure 50: Temperature contour plot (hemi valve open 10 degrees)
The temperature plot in Figure 50 shows a different profile of heat transfer when compared to
the factory model. The temperature profile is not as ‘long’, but ‘wider’, as the flow seems to
have dispersed heat sideward from the valve, as opposed to downstream; this is likely an
effect of reducing the flow area through the valve, causing a more gradual transfer of heat,
directed more prominently sidewards out of the valve.
The pressure contour plot shown in Figure 51 is very similar to the factory model, perhaps
showing slightly broader high and low pressure zones; again, a likely effect of reducing
outright flow capability. This also increases maximum pressure in the wastegate tract by
approximately 500Pa (from 4.327e3Pa to 4.822e3Pa).
Figure 51: Pressure contour plot (hemi valve open 10 degrees)

41
6.1.2 Twenty Degrees Open (Hemishpere)
Figure 52: Velocity streamlines of turbine exducer (hemi valve open 20 degrees)
Following the pattern seen in the factory models, Figure 52 shows that the profile of the
turbine flow has been altered more so with the 20 degree valve opening than with the 10
degree opening. The bulk flow stream appears to have retained its shape more so than with
the factory valve, with a similar amount of flow separation and recirculation. The hemisphere
valve appears to provide a slightly more laminar flow than the factory valve.
Figure 53 shows a much more uniform flow than the hemisphere valve open at 10 degrees.
The vortex after the wastegate valve also appears to be much less developed than with the
factory valve at 20 degrees, with the high velocity peaks (red colour on the streamlines)
appearing much more even in this hemisphere valve model. Lower face flow appears much
steadier with the hemisphere valve, along with the entire flow appearing more laminar and
more directionally focused towards the outlet. Again, there is an area of recirculating gas in
the lower right corner below the wastegate valve.
Figure 53: Velocity streamlines of wastegate valve (hemi valve open 20 degrees)

42
Figure 54: Temperature contour plot (hemi valve open 20 degrees)
Figure 54 shows signs of greater heat transfer across the flows than with the factory valve at
20 degrees, with high temperatures spreading laterally in to the turbine flow area more
noticeably. The wastegate flow also appears to have transferred a slightly larger amount of
heat downstream of the valve than with the factory setup.
Figure 55 shows a noticeably different pressure distribution, with lower relative pressure at
the top edge of the valve and in the area immediately after the valve. However, the pressures
in the hemisphere model are considerably higher than those in the factory model, showing
that the reduction in overall cross-sectional flow area through the valve causes a restriction
and a rise in pressure.
Figure 55: Pressure contour plot (hemi valve open 20 degrees)

43
6.2 Cone Valve
6.2.1 Ten Degrees Open (Cone)
Figure 56: Velocity streamlines of turbine exducer (cone valve open 10 degrees)
Figure 56 shows that the turbine exducer flow for the cone valve is slightly less focused than
with the hemisphere valve, with the flow being affected more by the wastegate flow. This
may be a sign that the wastegate valve is more volumetrically efficient, allowing more gas to
pass through the same valve at the same opening angle, adversely affecting the turbine flow.
This can be seen where the first reverse flow streamline has been ‘pushed’ further
downstream in this model.
Figure 57 shows a wastegate valve flow stream that is very similar to the hemisphere valve,
with a very large amount of turbulence and a well-developed vortex in the centre of the
stream. The flow stream of the wastegate appears to be interacting more with the stream of
the turbine exducer than in previous models, with similar lower face flow to the hemi model.
Figure 57: Velocity streamlines of wastegate valve (cone valve open 10 degrees)

44
Figure 58: Temperature contour plot (cone valve open 10 degrees)
The temperature plot in Figure 58 shows a broader spread of the hottest temperature region
than previous models. This indicates a higher degree of heat transfer, therefore signifying a
higher degree of cross-flow mixing of the wastegate gas in to the turbine flow stream. This
backs up the added turbulence seen in the wastegate flow streamlines on the previous page.
The maximum temperature in this model is also higher than previous models, and in fact,
unlike the previous models, higher than the input temperature of the wastegate gas by 4
degrees Kelvin (1277-1273).
The pressure contour plot in Figure 59 shows that the maximum and minimum pressure
regions are less defined, and that the values are less extreme than previous models. This is
another feature that reinforces the added turbulence, showing that the flow is less
concentrated in specific areas and is less steady.
Figure 59: Pressure contour plot (cone valve open 10 degrees)

45
6.2.2 Twenty Degrees Open (Cone)
Figure 60: Velocity streamlines of turbine exducer (cone valve open 20 degrees)
Figure 60 shows a more developed vortex within the turbine flow of the cone valve model at
20 degrees, also showing a higher degree of flow separation from the main turbine flow
stream. The upper right edge of the flow stream in the left-hand image above shows very
little disturbance from the introduction of the wastegate flow; whilst this may initially seem
like a good thing, it appears to also indicate that without the force of the wastegate flow
keeping the turbine stream in shape, the turbine flow will deviate to a greater extent near the
outlet.
The wastegate flow stream shown in Figure 61 illustrates a very turbulent flow, with a high
degree of recirculation and vortex formation after the waste valve. The lower face flow can
also be seen to separate from the wall near the outlet, also curving towards the turbine flow
around the same time. Again, there is an area of recirculating gas in the lower right corner
below the wastegate valve, perhaps appearing less prevalently than in other models.
Figure 61: Velocity streamlines of wastegate valve (cone valve open 20 degrees)

46
Figure 62: Temperature contour plot (cone valve open 20 degrees)
The temperature plot in Figure 62 shows a very large peak temperature region, indicating a
higher degree of flow mixing, which spreads the heat from the wastegate flow across the
downpipe surfaces to a greater extent. There is only a small amount of perpendicular flow
going across the turbine exducer, which is a positive aspect of this wastegate flow.
Figure 63 shows that the pressure distribution is very similar to that of the hemisphere valve,
however with a much higher peak pressure in the wastegate valve tract, indicating that this
cone valve restricts flow more so than the factory or hemisphere valves, causing more
backpressure before the wastegate valve.
Figure 63: Pressure contour plot (cone valve open 20 degrees)

47
6.3 Concave Cone Valve
6.3.1 Ten Degrees Open (Concave)
Figure 64: Velocity streamlines of turbine exducer (concave valve open 10 degrees)
Figure 64 shows that the turbine flow stream with the concave valve is very similar to the
hemisphere valve, with perhaps a slightly tighter flow stream due to more sideways force
from the wastegate stream. It can be expected that the wastegate flow changes direction
through 90 degrees more efficiently towards the turbine stream due to its sweeping, curved
design. There is a clear area of low pressure in the centre of the downpipe volume, where two
pairs of streamlines overlap as they are pulled out of the main flow stream and recirculated.
The wastegate flow stream in Figure 65 shows a much less turbulent flow than the
hemisphere and cone valves, with a less condensed vortex and smoother integration of flow
across in to the turbine stream. The streamlines across the lower surface appear to have a
straighter trajectory than previous valve models, indicating a more refined and laminar flow.
Figure 65: Velocity streamlines of wastegate valve (concave valve open 10 degrees)

48
The temperature and pressure contour plots were almost identical to the hemispherical valve
at 10 degrees of opening, so shall not be analysed here.
6.3.2 Twenty Degrees Open (Concave)
Figure 66: Velocity streamlines of turbine exducer (concave valve open 20 degrees)
The concave cone valve produced the most uniform, laminar turbine flow of all the valve
model simulations. The flow shown in Figure 66 is comparable to that of the system when the
wastegate valve is closed, only this model has no recirculation at all (at this streamline seed
point resolution). The interaction between the turbine flow and wastegate flow appears to be
most favourable to the turbine flow with this valve than any of the other designs.
Figure 67 shows that the flow stream of the wastegate is considerably more turbulent than the
turbine stream. There is a region of extreme recirculation right after the wastegate valve,
developing in to a vortex. This is likely an effect of the valves shape directing exhaust gases
smoothly outwards, perpendicular to the valve as opposed to the other valve designs that may
direct flow in a more outlet-biased direction. Whilst this central vortex may seem detrimental,
the streamlines of all the models suggest it may in fact be a necessary sacrifice for a more
laminar outwards flow along the downpipe walls and in-line with the turbine flow stream.
Figure 67: Velocity streamlines of wastegate valve (concave valve open 20 degrees)

49
Figure 68: Temperature contour plot (concave valve open 20 degrees)
The temperature plot in Figure 68 appears to have smooth and very defined boundaries
between the wastegate and turbine sides of the model, representing a steady, laminar flow
pattern as seen in the streamlines on the previous page. The highest temperature region is
narrow and extends all the way to the outlet face, another sign that the wastegate flow is
efficiently directing its energy (thermal and kinetic) in the desired direction.
The pressure plot in Figure 69 shows a more even pressure distribution around the valve face,
with slightly larger regions of higher pressure on the walls surrounding the valve (where the
flow is being directed towards). This may be a sign that the wastegate flow is being
channelled more evenly through the valve area and on to the downpipe/turbine housing walls
directly out of the valve.
Figure 69: Pressure contour plot (concave valve open 20 degrees)

50
6.4 Wedge Valve
6.4.1 Ten Degrees Open (Wedge – up/down)
Figure 70: Velocity streamlines of turbine exducer (wedge valve open 10 degrees)
The wedge valve produces a feature not seen in any previous models – a vortex formed from
the turbine exducer gases, as seen above in Figure 70. The main flow stream is very focussed
at the outlet face, with a fairly typical amount of flow separation from the main stream;
however it then forms a complex vortex with a large amount of flow recirculation. The bulk
flow stream seems to have suffered less severe deformation from the wastegate flow than in
some other models.
Figure 71 shows that the wastegate flow from the wedge valve appears to be more evenly
distributed between the upper and lower faces of the downpipe. There is a fair amount of
flow-mixing in to the turbine exducer stream; however there is minimal flow reversal and no
obvious vortex (although this feature has effectively been replaced by a turbine vortex).
Figure 71: Velocity streamlines of wastegate valve (wedge valve open 10 degrees)
The temperature plot was almost identical to the hemisphere valve, and the pressure plot
almost identical to the cone valve, hence they will not be analysed here.

51
6.4.2 Twenty Degrees Open (Wedge – up/down)
Figure 72: Velocity streamlines of turbine exducer (wedge valve open 20 degrees)
The flow stream of the wedge valve at 20 degrees (Figure 72) is comparable to that of the
factory valve at the same opening angle. There is a large degree of flow separation from the
bulk flow, and a high degree of torsional twist to the stream profile, directing flow lines
across the down pipe volume and intersecting the wastegate flow near the outlet. Flow is
separating early and merging with the recirculating volume of gas in the centre of the
wastegate flow stream.
Figure 73 shows the wastegate flow stream has a mild vortex with some recirculation, and
slightly more turbulent wall-flow than other valves. It is intriguing to note that this valve does
not produce the small pocket of recirculating gases seen in the corner of the housing below
the valve, as in most other valve models. As with the turbine flow, the wastegate flow is
comparable to the factory valve, however the flow here is slightly more focussed, featuring a
less direct vortex/recirculation system in the centre of the volume.
Figure 73: Velocity streamlines of wastegate valve (wedge valve open 20 degrees)

52
Figure 74: Temperature contour plot (wedge valve open 20 degrees)
The broad spread of peak temperature shown in Figure 74, all the way around the turbine
exducer circumference, indicates an undesirably high level of fluid mixing around this outer
area. While there is a narrow stream of gases flowing towards the outlet in line with the
wastegate, this initial perpendicular cross-flow shows a flow profile that is more prone to
cross-flow mixing at the turbine exducer than other models.
Figure 75 displays a larger area of minimum pressure on the upper valve seat surface than
other valve designs, and a much deeper area of low pressure extending in to the housing from
the valve towards the outlet (as seen on the upper side of the right hand image in Figure 75).
This may be occurring due to the region of recirculating gas in the central portion of the
wastegate flow stream, where there is often a vortex in other models. This may have been
pulling the gas flow away from the walls more so than other valve designs.
Figure 75: Pressure contour plot (wedge valve open 20 degrees)

53
6.4.3 Twenty Degrees Open (Wedge rotated 90 degrees – left/right)
Figure 76: Velocity streamlines of turbine exducer (rotated wedge open 20 degrees)
The streamlines shown in Figure 76 indicate that rotating the wedge valve did not improve
the flow stream – it in fact made it worse. There is a larger area of more extreme recirculation
in the primary vortex region; despite this, the remainder of the bulk flow stream does remain
well focused towards the right hand side of the outlet, with minimal twisting to the stream
shape.
The wastegate flow shown in Figure 77 may indicate why the bulk turbine flow stream
remain focussed on the outlet – the stream biased rightwards out of the valve appears to have
kept the turbine flow in its original shape for a longer period. This was detrimental to the
wastegate flow, however, as the large region of low pressure in the centre of the stream has
caused a large amount of gas recirculation that affected the turbine flow as well as the
wastegate flow. The lower wall flow appears to have little flow separation, which is good.
Figure 77: Velocity streamlines of turbine exducer (rotated wedge open 20 degrees)

54
Figure 78: Temperature contour plot (rotated wedge open 20 degrees)
As seen in Figure 78, the left/right directional flow-bias of this rotated valve gives rise to a
small bubble of heat transfer pushing in to the turbine stream surrounding walls. Correlating
to the focussed appearance of the turbine stream in Figure 76, this bubble soon disappears
and it can be seen that the lateral heat transfer is kept to a minimum after this point. The
wastegate flow shows a broad temperature profile extending towards the outlet, indicating a
less focussed flow from the wastegate.
The pressure contour plot shows a fairly average area of low pressure above the valve, with
more of a pressure focus on the left and lower side of the valve area. Pressure remains fairly
low extending out from the valve, indicating a slightly more gradual pressure drop as the flow
moves through the valve area, possibly from a lower degree of wall flow separation keeping
local flow velocities high.
Figure 79: Pressure contour plot (rotated wedge open 20 degrees)

55
6.5 Pyramid Wedge Valve
6.5.1 Ten Degrees Open (Pyramid)
Figure 80: Velocity streamlines of turbine exducer (Pyramid valve open 10 degrees)
Figure 80 shows a less steady flow stream with the pyramid valve, where several streamlines
separate from the bulk flow and recirculate in an unusually turbulent manner. The stream is
less focused on the outlet face, with the effect of the wastegate flow seeming to slow the
turbine flow more drastically than some other models.
Studying Figure 81, it can be seen that the wastegate valve flow features a well-developed
central vortex, forming soon after the valve. It seems the pyramid valve causes a prominent,
turbulent vortex to form, along with fairly typical flow-mixing and streamline separation
elsewhere. There is also some severe recirculation in the lower-central area of the downpipe,
where a smaller, unusually shaped secondary vortex may be present.
Figure 81: Velocity streamlines of wastegate valve (Pyramid valve open 10 degrees)
The temperature contour plot appeared very similar to the factory valve opened to 10 degrees,
as did the pressure contour plot, so neither will be shown here.

Part B Individual Engineering Project Report - 11011794

Part B Individual Engineering Project Report - 11011794

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