The document describes how simulation, wind tunnel testing, and road tests are used complementarily during the aerodynamic development of a new BMW SUV. Simulation is used early on to assess styling themes when only basic vehicle geometry is available. More detailed models are later tested in wind tunnels to evaluate underhood flow and component temperatures. Road tests evaluate real-world issues like soiling and snow deposition that other methods cannot fully replicate. Each tool has advantages and limitations, so clever application at the right time helps shorten development cost and time.
Fluid-Structure Interaction Over an Aircraft WingIJERDJOURNAL
ABSTRACT:- Aircraft is a brilliant man-made structure which helps us to fly over the world. At the same time, aircraft is a complex structure to be checked and maintained for the aero elasticity due to aerodynamic properties. In this paper, the fluid-structure interaction problem in super critical NASA SC(2)-0412 airfoil is discussed. The main aim of this project is to find the best performance and deformation limit of the wing on different Mach numbers. This project is completely done by numerical methods of designing the wing using CATIA and flow properties in Computational Fluid Dynamics (CFD) method. Finally, the structural analysis for deformation is analysed in ANSYS. The analytical approach of fluid-structure interaction over an Aircraft wing is complex.
Experimental Investigations to Study the Air Flow Patterns on the Headlight D...IJERA Editor
This paper presents some experimental investigations to study the air flow patterns on the headlight domes of different two wheelers (HERO HONDA PASSION PLUS and BAJAJ PULSAR) which influence the stability of the vehicle. The pressure distribution over the surface of the profile and the drag force are to be determined for various headlight dome orientations. This study helps in suggesting the suitable headlight dome profile that may reduce the drag force and effect of turbulence which in turn leads to the increase of vehicle stability. The results obtained during the simulation are to be validated by conducting the experiments on the scale down model of the headlight dome of HERO HONDA PASSION PLUS using Wind Tunnel test rig. The Computational Fluid Dynamics (CFD) tool was used to simulate the air flow pattern on the headlight dome in which boundary layer separation doesn’t exist. The results obtained from the simulation are to be compared with the experimental results from the wind tunnel and the variation is to be found and that should be in the acceptable limit.
Fluid-Structure Interaction Over an Aircraft WingIJERDJOURNAL
ABSTRACT:- Aircraft is a brilliant man-made structure which helps us to fly over the world. At the same time, aircraft is a complex structure to be checked and maintained for the aero elasticity due to aerodynamic properties. In this paper, the fluid-structure interaction problem in super critical NASA SC(2)-0412 airfoil is discussed. The main aim of this project is to find the best performance and deformation limit of the wing on different Mach numbers. This project is completely done by numerical methods of designing the wing using CATIA and flow properties in Computational Fluid Dynamics (CFD) method. Finally, the structural analysis for deformation is analysed in ANSYS. The analytical approach of fluid-structure interaction over an Aircraft wing is complex.
Experimental Investigations to Study the Air Flow Patterns on the Headlight D...IJERA Editor
This paper presents some experimental investigations to study the air flow patterns on the headlight domes of different two wheelers (HERO HONDA PASSION PLUS and BAJAJ PULSAR) which influence the stability of the vehicle. The pressure distribution over the surface of the profile and the drag force are to be determined for various headlight dome orientations. This study helps in suggesting the suitable headlight dome profile that may reduce the drag force and effect of turbulence which in turn leads to the increase of vehicle stability. The results obtained during the simulation are to be validated by conducting the experiments on the scale down model of the headlight dome of HERO HONDA PASSION PLUS using Wind Tunnel test rig. The Computational Fluid Dynamics (CFD) tool was used to simulate the air flow pattern on the headlight dome in which boundary layer separation doesn’t exist. The results obtained from the simulation are to be compared with the experimental results from the wind tunnel and the variation is to be found and that should be in the acceptable limit.
Design and Development of Transonic Axial Flow Compressor Rotor BladeIJERDJOURNAL
Abstract:- This paper is about a new computational fluid dynamics developed for the transonic flow in a compressor rotor. Due to 3-Dimensional blade modification the arrangements satisfying the required boundary condition. Engine compressor towards distorted inflow has to be taken in account which is already in the design phase. Flow separation over the blade surface reduction and elimination can improve better aerodynamic, performance, efficiency and stall margin. NASA transonic rotor tip critical in baseline blade rotor performance energizing the low momentum boundary layer, controlling the inception of stall. A Profile generator are attached on the inner casing of the rotor ahead to the loading edge of the rotor and it is influenced on the overall performance which has been studied.
An efficient algorithm for ogee spillway discharge with partiallyopened radia...theijes
Ogee profile flood spillways equipped with radial gates are common, and accurate computation of spilled discharge through partially-opened radial gates is an important problem. A new algorithm is developed for the method given in the latest edition of the book: Design of Small Dams for computation of discharge over ogee spillways equipped with radial gates for the partial opening case. This algorithm is more efficient with less computational load than the one presented in ‘Hydraulic Design Criteria, Sheets 311-1 to 311-5’ by US Army Corps of Engineers which is the method by ‘Design of Small Dams’. For a wide range of partial gate openings on a few existing dams, discharges are computed by this method and are compared with those given by the previous method comprised in the former editions of ‘Design of Small Dams’. As both yield close values for small gate openings, the current method gives spillway discharges about 10 % to 30 % greater than the previous method for large gate openings. Next, discharge coefficients are computed using the measured data taken on 1:50 scale laboratory model of the spillway of Kavsak Dam and are compared with those given by the charts in ‘Design of Small Dams’, which are found to be deviant as much as 10 %.
CFD Studies of Blended Wing Body Configuration for High Angles of Attack -- Z...Abhishek Jain
Above Research Paper can be downloaded from www.zeusnumerix.com
Blended Wing Body (BWB) configurations offer a unique advantage of generating lift from the fuselage. The research paper aims to study several configurations aerodynamically for the viability of use in actual flight. The code is validated using the configuration from UiTM Malaysia. Simulations are performed at high angles of attack ranging from 20 deg to 40 deg. Good agreement is seen in RANS CFD and low speed wind tunnel data. The comparison gives confidence that BWB can be simulated at high angles of attack. Authors - Irshad Khan and Deepak Patil (Zeus Numerix), DN Santhosh (SDM CoE)
Flow Modification over Rotor Blade with Suction Boundary Layer Control TechniqueIJERA Editor
The efficiency of transonic aircraft engines depend upon the performance of compressor rotor. To increase
compressor rotors performance flow separation around rotor blades must be delayed and controlled. The aim
was to control the flow separation of blades using suction boundary layer control method.
Rotor blade has been modelled in designing software CATIA and then a suction surface has been created on
blade and then import these geometries to ANSYS-CFX 14.5 for computational analysis of flow around blades.
Suction slot has been applied at the trailing edge of suction surface and Shear stress transport model has been
used for computational analysis.
Two different suction mass flow rates 1 kg/s and 1.5 kg/s have been used here and boundary layer separation
effects have been changed and this could be readily seen that the velocity vectors have reattached, preventing
the boundary layer separation at the suction surface of the blade.
Design and Development of Transonic Axial Flow Compressor Rotor BladeIJERDJOURNAL
Abstract:- This paper is about a new computational fluid dynamics developed for the transonic flow in a compressor rotor. Due to 3-Dimensional blade modification the arrangements satisfying the required boundary condition. Engine compressor towards distorted inflow has to be taken in account which is already in the design phase. Flow separation over the blade surface reduction and elimination can improve better aerodynamic, performance, efficiency and stall margin. NASA transonic rotor tip critical in baseline blade rotor performance energizing the low momentum boundary layer, controlling the inception of stall. A Profile generator are attached on the inner casing of the rotor ahead to the loading edge of the rotor and it is influenced on the overall performance which has been studied.
An efficient algorithm for ogee spillway discharge with partiallyopened radia...theijes
Ogee profile flood spillways equipped with radial gates are common, and accurate computation of spilled discharge through partially-opened radial gates is an important problem. A new algorithm is developed for the method given in the latest edition of the book: Design of Small Dams for computation of discharge over ogee spillways equipped with radial gates for the partial opening case. This algorithm is more efficient with less computational load than the one presented in ‘Hydraulic Design Criteria, Sheets 311-1 to 311-5’ by US Army Corps of Engineers which is the method by ‘Design of Small Dams’. For a wide range of partial gate openings on a few existing dams, discharges are computed by this method and are compared with those given by the previous method comprised in the former editions of ‘Design of Small Dams’. As both yield close values for small gate openings, the current method gives spillway discharges about 10 % to 30 % greater than the previous method for large gate openings. Next, discharge coefficients are computed using the measured data taken on 1:50 scale laboratory model of the spillway of Kavsak Dam and are compared with those given by the charts in ‘Design of Small Dams’, which are found to be deviant as much as 10 %.
CFD Studies of Blended Wing Body Configuration for High Angles of Attack -- Z...Abhishek Jain
Above Research Paper can be downloaded from www.zeusnumerix.com
Blended Wing Body (BWB) configurations offer a unique advantage of generating lift from the fuselage. The research paper aims to study several configurations aerodynamically for the viability of use in actual flight. The code is validated using the configuration from UiTM Malaysia. Simulations are performed at high angles of attack ranging from 20 deg to 40 deg. Good agreement is seen in RANS CFD and low speed wind tunnel data. The comparison gives confidence that BWB can be simulated at high angles of attack. Authors - Irshad Khan and Deepak Patil (Zeus Numerix), DN Santhosh (SDM CoE)
Flow Modification over Rotor Blade with Suction Boundary Layer Control TechniqueIJERA Editor
The efficiency of transonic aircraft engines depend upon the performance of compressor rotor. To increase
compressor rotors performance flow separation around rotor blades must be delayed and controlled. The aim
was to control the flow separation of blades using suction boundary layer control method.
Rotor blade has been modelled in designing software CATIA and then a suction surface has been created on
blade and then import these geometries to ANSYS-CFX 14.5 for computational analysis of flow around blades.
Suction slot has been applied at the trailing edge of suction surface and Shear stress transport model has been
used for computational analysis.
Two different suction mass flow rates 1 kg/s and 1.5 kg/s have been used here and boundary layer separation
effects have been changed and this could be readily seen that the velocity vectors have reattached, preventing
the boundary layer separation at the suction surface of the blade.
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CFD Simulation for Flow over Passenger Car Using Tail Plates for Aerodynamic ...IOSR Journals
This work proposes an effective numerical model based on the Computational Fluid Dynamics
(CFD) approach to obtain the flow structure around a passenger car with Tail Plates. The experimental work of
the test vehicle and grid system is constructed by ANSYS-14.0. FLUENT which is the CFD solver & employed in
the present work. In this study, numerical iterations are completed, then after aerodynamic data and detailed
complicated flow structure are visualized.
In the present work, model of generic passenger car has been developed in solid works-10 and
generated the wind tunnel and applied the boundary conditions in ANSYS workbench 14.0 platform then after
testing and simulation has been performed for the evaluation of drag coefficient for passenger car. In another
case, the aerodynamics of the most suitable design of tail plate is introduced and analysedfor the evaluation of
drag coefficient for passenger car. The addition of tail plates results in a reduction of the drag-coefficient
3.87% and lift coefficient 16.62% in head-on wind. Rounding the edges partially reduces drag in head-on wind
but does not bring about the significant improvements in the aerodynamic efficiency of the passenger car with
tail plates, it can be obtained. Hence, the drag force can be reduced by using add on devices on vehicle and fuel
economy, stability of a passenger car can be improved.
Performance Study of Wind Friction Reduction Attachments for Van Using Comput...IJERA Editor
Road transport is the key factor as it is the major method to connect places through land. Along with wide use of internal combustion engines for this purpose comes the massive consumption of fossil fuels by vehicles. Most of the research today is toward making efficient machines. This paper mainly deals with providing attachments to existing models of vehicle to make it more efficient. An assessment of the impact of aerodynamic drag and its relationship to energy consumption presented. A few models are designed and analysed for reducing drag with the help of Attachments. Solid works is used to model and ANSYS Fluent is used for CFD analysis. The results of Cd of various configuration is analysed, 0.427 being the Cd for conventional Van is reduced to 0.234 for van with front and rear attachment
Performance Study of Wind Friction Reduction Attachments for Van Using Comput...IJERA Editor
Road transport is the key factor as it is the major method to connect places through land. Along with wide use of internal combustion engines for this purpose comes the massive consumption of fossil fuels by vehicles. Most of the research today is toward making efficient machines. This paper mainly deals with providing attachments to existing models of vehicle to make it more efficient. An assessment of the impact of aerodynamic drag and its relationship to energy consumption presented. A few models are designed and analysed for reducing drag with the help of Attachments. Solid works is used to model and ANSYS Fluent is used for CFD analysis. The results of Cd of various configuration is analysed, 0.427 being the Cd for conventional Van is reduced to 0.234 for van with front and rear attachment.
Design modification on Indian Road Vehicles to Reduce Aerodynamic DragIJAEMSJORNAL
Reducing vehicle fuel consumption has become one of the most important issues in recent years. Aerodynamic drag contributes to 50-60% of fuel consumption in trucks on highways. Vehicle aerodynamic performance is mainly determined by drag coefficient, which directly affects engine requirements and fuel consumption. It’s well known that drag changes in a crosswind compared with a condition without a crosswind, and that the change depends on the vehicle shape. Pressure drag, a major drag for trucks as they run at lower speeds is produced by the shape of the object. Therefore, addition of some components can suffice the need. The vehicle has been designed by using Catia and then analysed with CFD. The values are compared and the resultant drag reduction is calculated.
ADVANCED TOOL FOR FLUID DYNAMICS-CFD AND ITS APPLICATIONS IN AUTOMOTIVE, AERO...IAEME Publication
Today Automotive, Aerospace and Machine industry is striving for better Efficiency and Design. Advanced tools like Computation Fluid Dynamics (CFD) may be used for improving the fuel efficiency of these and hence controlling the atmospheric air pollution. In this paper, CFD analysis software is used a) to study fluid flow and detect the cavitation in centrifugal pump to find out safe operating conditions b) to find out effect of front shape to improve drag coefficient of a car. The results of the simulation shows, how CFD can be used to study flow distribution, pressure loss, thermal distribution (cooling and climate control) in the field of Automotive, Aerospace and Machine industries.
Automotive aerodynamics is the study of the aerodynamics of road vehicles. Its main goals are reducing drag and wind noise, minimizing noise emission, and preventing undesired lift forces and other causes of aerodynamic instability at high speeds. Air is also considered a fluid in this case.
FLUID FLOW ANALYSIS OF CENTRIFUGAL FAN BY USING FEMIAEME Publication
The forward backward curved (mixed) Centrifugal fan 630 has been analyzed aerodynamically for compare experimental results with simulation results by using ANSYS FLUENT (Finite Element Analysis Software). The material of the fan impeller was specified as ALUMINIUM. Boundary conditions on the Centrifugal fan-630 are taken from the reference. The flow distribution across the fan is obtained. The maximum static pressure at the inlet is known and the pressure distributions across the blade are obtained accordingly. The obtained results are compared with Experimental results is discussed. In final recommended the design of the centrifugal fan and results are tabulated. It’s observed that simulation results are nearer to the experimental results.
Design of Rear wing for high performance cars and Simulation using Computatio...IJTET Journal
The performance of a sports car is not only limited to its engine power but also to aerodynamic properties of the car. By decreasing the drag force it is possible to reduce the engine power required to achieve same top speed thus decreasing the fuel requirement. The stability of a sports car is considerably important at high speed. The provision of a rear wing increases the downforce thus reducing the rear axle lift and provides increased traction. In this study an optimum rear wing is designed for the high performance car so as to decrease drag and increase downforce. The CAD designed baseline model with or without rear wing is being analyzed in computational fluid dynamics software. The lift and drag coefficient are calculated for all the design thus an optimum rear wing is designed for the considered baseline model.
Wind-induced Stress Analysis of Front Bumpertheijes
At high velocities, such as on highways, the relative velocity between the oncoming wind and side winds is very high. The high velocity winds that act on the bumper induce certain stresses on it. These stresses may cause deformation of the bumper; if this deformation exceeds a predesigned value, the functionality of the bumper may be hampered. This may result in safety issues and other design issues. In this paper, the effect and nature of these stresses have been quantified by conducting a wind-induced stress analysis on a model of the bumper. The bumper selected is that of Jeep Wrangler and the modelling is done on Creo 2.2. The CFD simulation and structural analysis is conducted on Ansys Workbench 15. The structural analysis and fluid flow data is summarized alongwith the deformation and induced stress values.
1. F2006M035
COMPLEMENTARY USAGE OF SIMULATION, WIND TUNNEL AND
ROAD TESTS DURING THE AERODYNAMIC DEVELOPMENT OF A
NEW BMW SUV
Kerschbaum, Hans*
, Grün, Norbert
BMW Group, Germany
KEYWORDS – Aerodynamics, CFD, Simulation, Wind Tunnel, Road Test
ABSTRACT - In the course of the entire vehicle development process aerodynamics is one of
the few disciplines involved from the very early initial phase up to the final serial
development. Along this cycle the available data features very different levels of detail.
After the kick-off of a new model only generic bodies without underhood and underbody
details are provided from styling for the aerodynamic analysis and ranking of different
themes. These may be clay models or virtual shapes created with ALIAS. Once the design
competition is completed and the exterior skin is frozen, more and more details of the engine
compartment and the underbody become available to the aerodynamicist from various other
departments.
According to the growing maturity of product data also the problems to be addressed are
changing. The initial ranking of styling themes with respect to aerodynamic quality is mostly
accomplished purely based on drag and lift distribution. However, aerodynamics is closely
linked with thermal management and therefore cooling air mass flow rates, performance of
the cooling package and component temperatures need to be assessed as soon as the necessary
geometry data is available. Another constraint arises from the short time windows in the
overall development process in which the aerodynamicist can have an impact on the vehicle.
To cope with these tasks the aerodynamicist uses a toolbox consisting of
• Simulation (CFD)
• Wind Tunnel
• Road Test
At the BMW group these tools are not considered as competing instruments, rather they are
used in a complementary fashion. Each tool has its own advantages and drawbacks and
therefore only their clever application to the right problem at the right time delivers a real
benefit and aids to shorten cost and time.
This paper exemplifies this process in detail on the aerodynamic development of a new BMW
SUV to be released in autumn 2006.
2. INTRODUCTION
The objective of this paper is to describe the complementary usage of simulation, wind tunnel
and road testing during the aerodynamic development of a new SUV.
Aerodynamics is the first engineering discipline to assess properties of styling models and is
further involved throughout the entire development process, see Fig. 1 from (1). Even before
a styling competition starts, various proportion studies are already judged by their potential in
terms of drag and lift forces. During the reduction of different design themes up to styling
freeze, aerodynamics has a significant impact on the decision which models to drop.
However, the time window to exert influence is very short and requires an optimized toolbox
for an efficient aerodynamic development process.
Fig. 1: The Aerodynamic Development Process (1)
According to the increasing level of detail available to the aerodynamicist over time it
becomes possible to tackle more and more complex problems (Fig.2). Initially when only
generic bodies are provided from styling the properties which can be assessed are integral
forces and moments. Usually only virtual models exist at this time and CFD simulation is the
tool of choice.
Fig. 2: Problems and Tools
3. However, even at this stage the flow through the engine compartment is already represented
in a simplified manner to include its influence on the external aerodynamics.
During design competition in the concept phase the most promising variants are also milled as
40% scale models and tested in the wind tunnel. Here it is possible to determine the potential
because 10-20 variants can easily be created and measured per day, a rate which CFD can not
yet keep pace with. However, the simulation results deliver valuable hints for this
optimization process upfront. Like in the simulation models the cooling package is included
to gain information about the expected cooling air mass flow rates.
Since aerodynamics, namely side force, rear lift and yawing moment, can have a strong
impact on driving stability, the behaviour under gusty side winds is analysed by transient
simulations using time-dependent boundary conditions.
Thermal management problems, especially for underbody components like gearbox or rear
axle transmission, can be tackled as soon as more detailed geometry data is available. This is
achieved by looking at heat transfer distribution from the simulation or later by measuring
component temperatures when drivable prototypes exist.
The capability to assess soiling properties and in particular snow deposition via simulation is
still very limited. Therefore these investigations currently have to wait until road tests are
possible. However, changes in this phase are very expensive and frontloading is the key to
reduce development cost.
SIMULATION
Almost ten years ago BMW started to validate PowerFLOW (2-4), a Lattice-Boltzmann code,
to simulate vehicle aerodynamics. The level of maturity reached to date allows to handle very
detailed models and to assess not only external aerodynamic properties but also characteristics
relevant for thermal management already in the early phase of the development process.
Fig. 3: Virtual Model for CFD (Computational Fluid Dynamics) Simulation
The simulation model (Fig. 3) is composed by any number of solids and zero-thickness shells,
represented by facetized surfaces. Usually the outer skin is created with CAS tools like
ALIAS or, if the stylist prefers to work with clay models, is obtained by laser scanning.
4. Underhood and underbody components like engine, drivetrain and wheel suspensions are
extracted from database systems and updated permanently to reflect the progress in geometry
definition. In the early phase where these details are not yet available, information from the
predecessor is used.
Fig. 4: Visualization of Simulation Results
The raw result of a simulation are fluid dynamic quantities at millions of points in space and
time. Only appropiate visualization and analysis tools can translate this information into
valuable engineering data. Typical display features are surface pressures and wall streamlines
as well as 3D streamlines and the distribution of total pressure loss in the flow field (Fig.4).
If the properties of cooling package components in terms of pressure loss and heat transfer are
known, the cooling air mass flow rate and the actually transferred heat can already be
evaluated in the early phase of development. Even from an isothermal simulation the
distribution of heat transfer can be deduced to check for instance wether drivetrain
components are properly cooled or require modifications of underbody panels (Fig.5).
Fig. 5: Distribution of Heat Transfer (red = high , blue = low)
5. Fig. 6: Analysis of Drag Generation
The highest level of data reduction is the integration of surface pressure and skin friction to
obtain integral forces and moments, equivalent to a wind tunnel measurement. However, this
does not allow in-depth investigation in case of unexpected results. One example for the
advanced analysis capabilities of simulation is shown in Fig.6 where the vehicle is cut in
slices whose contribution to total drag is displayed as a bar chart. In addition, the integration
downstream is shown as a solid line, ending at the vehicle’s total drag. Clearly visible are
those regions with high drag generation like front end, cooling package, wheels and rear end
base. However, also negative drag contributions can be identified where low pressure is
acting upon forward facing parts of the surface. This analysis is particularly valuable to
compare two variants by simply looking at the differences of these drag distributions.
Depending on the flow field topology in the
wake, it may happen that exhaust gas enters
the passenger compartment through leaks of
the rear door. By prescribing the exhaust
gas exit velocity and temperature it is
possible to visualize the (unsteady) exhaust
gas plume via isosurfaces of any
temperature (Fig.7). This enables the
optimization of end pipe position and
direction or, if necessary, even the
prevention of exhaust gas recirculation by
appropriate modifications of the rear end
geometry which would be very cost-
intensive if detected later during road tests.
Fig. 7: Exhaust Gas Plume .
6. WIND TUNNEL TESTING
For reasons of cost and easy handling
early wind tunnel testing is conducted
using 40% scale models. However,
already in this phase underhood and
underbody flow is accounted for in a
simplified manner. Fig.8 displays the
modular assembly of such a model.
The actual styling geometry is milled in
PU-foam and mounted on top of a frame
holding the wind tunnel balance which in
turn will be connected to the supporting
strut. A second frame houses STL parts
representing the drivetrain and underbody
panels. A radiator simulator can be
adjusted to produce pressure losses of
production heat exchangers. It is also
possible to measure the actual cooling air
mass flow rate with this equipment. This
supporting structure is universal, i.e. it can
be used with almost all vehicle types.
Currently the BMW full scale tunnel has a
stationary floor with boundary layer
suction. For model testing with ground
simulation it can be equipped with a
moving belt device where the wheels are
supported by external arms separately
from the vehicle body and driven by the
belt (Fig.9, left). Large scale shape
modifications (Fig.10) can easily be tested
this way and it is possible to assess more than 20 variants per wind tunnel shift. Details and
limitations of the transferability from model to full scale are discussed in (5).
Fig. 8: Exploded View of a Modular
40% Scale Model (1)
Fig. 9: Model (left at BMW) and Full Scale (right at FKFS) Testing in the Wind Tunnel
7. Fig. 10: Shape Modification in the Wind Tunnel (40% Scale Model in Foam and Clay)
Even before design freeze selected variants are also milled in full scale and put together in a
similar modular assembly because detail optimization like A-pillar contour or radii of critical
edges is questionable in model scale. For these tests external wind tunnels like the one from
FKFS in Stuttgart (6) with a 5-belt system (Fig. 9, right) are used if it is felt that this level of
ground simulation is necessary.
ROAD TESTS
The aerodynamic problems investigated on the road using drivable prototypes are those where
neither simulation nor the wind tunnel can reproduce reality close enough.
A typical example is soiling where it is tested how dust and dirt thrown off by the wheels are
propagated in the flow field and where it impinges on the surface. Apart from keeping door
handles and frames clean, the goal is to guarantee visibility through the rear window and the
side glass onto the wing mirror. To obtain reproducable conditions the vehicle is driven a
couple of times with constant speed through a bed covered with a chalk-like material of grain
size 1/10mm (Fig.11, left). The test track can also be flooded to distinguish dry and wet
soiling. Before and after the tests the vehicle is photographed in a dark room under the same
perspective and lighting conditions. Via image processing it is then possible to generate a
false color rendering for documentation and comparison among different vehicles (Fig.11,
right).
Fig. 11: Road Test (Soiling)
Similar tests are conducted under winter conditions to analyze the deposition of snow. Here
the focus is extended on keeping the rear lights and all air intakes for engine, cooling, brakes
8. and HVAC clear (Fig.12, left). Sometimes snow could even change the overall aerodynamic
properties by accumulating at devices like the roof spoiler in Fig.12, right.
Fig. 12: Road Test (Snow Deposition)
Another test which can not yet be simulated or made in the wind tunnel reliably is the
management of rain water. It has to be ensured that A-pillar and roof corner are designed to
keep the view on the wing mirror unobstructed and to avoid that water enters the passenger
compartment when side window or door are opened.
Although thermal management is explored by simulation and wind tunnel as much as
possible, there are always final road tests under extremely hot and cold environmental
conditions where the surface temperatures of critical components are recorded.
SUMMARY AND CONCLUSION
It has been demonstrated how the different tools (simulation, wind tunnel and road testing)
are employed in a complementary fashion for the aerodynamic development of a new SUV.
Realizing the advantages and drawbacks of each method, a benefit.in terms of cost and time
can only be achieved by a clever combination and application of these tools to the right
problem at the right time. It is desirable to move as much tests as possible upfront because the
later requests come up the more cost-intensive and time-consuming these changes will be.
NOTE
Due to the early deadline for submission of the printed paper well before the launch of the
SUV, images of the predecessor had to be used here.
REFERENCES
(1) Hans Kerschbaum, Norbert Gruen, Peter Hoff, Holger Winkelmann, “On Various
Aspects of Testing Methods in Vehicle Aerodynamics”, JSAE Paper 20045445,
Yokohama, Japan, 2004
(2) H. Chen, “Volumetric Formulation of the Lattice-Boltzmann Method for Fluid
Dynamics: Basic Concepts”,Physical Review E, Volume 58, Number 3, September
1998
(3) Wolf Bartelheimer, “Validation and Application of CFD to Vehicle Aerodynamics”,
JSAE Paper 20015332, Yokohama, Japan, 2001
9. (4) Norbert Gruen, “Application of a Lattice-Boltzmann Code in Vehicle Aerodynamics”,
von Karman Institute for Fluid Dynamics, Brussels, Belgium, Lecture Series 2005-05,
2005
(5) Jochen Thibaut, “Optimization of Vehicle Design regarding Internal Airflow in the
Aerodynamic Development Process”, FISITA Paper F2006M157, 2006
(6) Jochen Wiedemann, Juergen Pothoff , “The New 5-Belt Road Simulation System of
the IVK Wind Tunnels”, SAE Paper 03B-102, 2003