Ijmet 09 11_016

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International Journal of Mechanical Engineering and Technology (IJMET)
Volume 9, Issue 11, November 2018, pp. 130–145, Article ID: IJMET_09_11_016
Available online at http://www.iaeme.com/ijmet/issues.asp?JType=IJMET&VType=9&IType=11
ISSN Print: 0976-6340 and ISSN Online: 0976-6359
© IAEME Publication Scopus Indexed
NUMERICAL INVESTIGATION OF MIXING
PROPERTY OF FUEL AND AIR IN SWIRL
COMBUSTOR
A.Ravinthiran
Faculty of Mechanical Engineering
Sri Sairam Engineering College, Chennai
V. Prasanna, B. Karthik, V. Naveen, Mohammed Suhail and S. Hayagreevan
Department of Mechanical Engineering
Sri Sairam Engineering College, Chennai
ABSTRACT
A general interest to reduce fossil fuel consumption and to limit combustion
emissions, increase the efficiency of combustion chambers. One of the most important
processes in a gas turbine combustor, influencing to a large extent the efficiency of the
entire combustion process is the mixing between a swirling annular jet (primary air) and
the non-swirling inner jet (fuel).In normal swirling combustor, primary swirling air is
only supplied to the chamber and is mixed with the fuel but we here introduce a small
duct in the chamber containing a small amount of air without swirl and make it to mix
with the fuel and the primary swirling air. We have modified the design of the swirl
combustor by introducing a bluff body over the flow of the turbulent jet through which the
turbulent air will pass causing the axial velocity. For the purpose of simulation of the
required model of swirl combustor we are using the recent tools like ANSYS, ICEM, CFD
and FLUENT software’s. Using these tools the numerical investigation has been done.
The various values that are obtained are compared with the previous results of the swirl
combustor and the increase in the efficiency of the combustion has been noted.
Keywords: Fossil fuel, Combustion Chamber, Swirling Annular Jet, Bluff Body,
Numerical Investigation.
Cite this Article A.Ravinthiran, V. Prasanna, B. Karthik, V. Naveen, Mohammed Suhail
and S. Hayagreevan, Numerical Investigation of Mixing Property of Fuel and Air in Swirl
Combustor, International Journal of Mechanical Engineering and Technology, 9(11),
2018, pp. 130–145.
http://www.iaeme.com/IJMET/issues.asp?JType=IJMET&VType=9&IType=11

A.Ravinthiran, V. Prasanna, B. Karthik, V. Naveen, Mohammed Suhail and S. Hayagreevan
1. INTRODUCTION
Nitrogen oxides (NOx) generate photochemical smog and haze, therefore controlling these gases
is crucial for the air quality in the lower atmosphere. In addition, in the higher atmosphere, NOx
is a precursor to destroy the ozone and as such, e.g. airplanes flying at cruising altitudes contribute
to the depletion of the ozone layer. Although vehicle emissions are responsible for a substantial
part of NOx emissions, many stationary sources that burn natural gas also emits significant
amount of NOx. Domestic heating appliances more and more use natural gas burners at the
expense of coal or oil red equipment for reasons of easy maintenance, compactness, availability
of the fuel and the common sense of using a cleanfuel. Natural gas burners used in boilers and
furnaces in many cases provide the heat for manufacturing, industrial processing or space
conditioning. Today, the recently developed high efficient power plants apply modern gas turbine
technology that makes use of natural gas. A growing concern about good air quality drives the
search for low emission combustion techniques. Simultaneously increasing the thermal efficiency
is also of equal importance in order to reduce the total amount of energy consumed. Conventional
natural gas combustion easily produces NOx in the order of several hundreds of mg/Nm3 in boiler
utilities. In high temperature environments, such as furnaces and ovens, the uncontrolled NOx
levels reach thousands of mg/Nm3.
The mixing of the swirling annular jet (primary air) and the non-swirling inner jet (fuel)
represents one of the most important processes in a gas turbine swirl combustor, influencing to a
large extent the efficiency of the entire combustion process [1, 3]. A recirculation zone generated
in the center of a swirl combustor enhances flame stability and is a usual design concept of
combustors. Additionally, the flow field is influenced by the effects of combustion in several
ways. Even restricting the attention only to the isothermal case, an exceedingly complex flow
pattern arises, exhibiting several simultaneously occurring phenomena. Numerous experimental
investigations serving for years as benchmarks for computational methods and turbulence model
validation have been conducted in the past. Swirl flows are widely used in various technical
devices and technological processes especially in the reacting flow, where the existence of
recirculation zones leads into the increase of efficiency of chemical reaction and stabilization of
processes. Due to the permanent increase in the development of these devices, experimental
investigation and mathematical modeling of swirl turbulent flow are very important. For the
purpose of computer simulation of gaseous fuel burners and combustion chambers a
mathematical model and numerical solution procedure, for the prediction of the turbulent swirl
flow with heat and mass transfer for combustion in two-dimensional geometries: plane and
axisymmetrical was developed [5-7]. In this work the model was applied to the analysis of swirl
combustion chamber. The separated re-circulating flow which is established in the near vicinity
of bluff bodies can be used to stabilize flames in high velocity reactant streams. There had been
many experimental investigations carried out to study the bluff body wakes. The details of
aerodynamics of the near wake are crucial to the description of the mechanism of stabilization.
For example, the size of the recirculation zone affects the rate of production of hot burnt products
and the mixing between these products and the reactants is governed by the turbulence in the free
shear layers.
2. EXPERIMENTAL SETUP
2.1 Swirl chamber
It consists of a spherical chamber located in the cylinder head and separated from the engine
cylinder by a tangential throat as shown in Fig. 1.

Numerical Investigation of Mixing Property of Fuel and Air in Swirl Combustor
Figure 1 Combustion in a swirl chamber.
About 50% of the air enters the swirl chamber during the compression stroke of the engine,
producing a swirl. After combustion, the products return through the same throat to the main
cylinder at much higher velocity. So more heat loss to walls of the passage takes place[4]. This
type of chamber finds application in engines in which fuel control and engine stability are more
important than fuel economy. Here in this project we have made an blockage to make it rotate
with the direction of the swirl and with no rotation of the swirl.
2.2 Turbulence Modeling In CFD
A turbulence model is a computational procedure to close the system of mean flow equations.
For most engineering applications it is unnecessary to resolve the details of the turbulent
fluctuations. Turbulence models allow the calculation of the mean flow without first calculating
the full time-dependent flow field. We only need to know how turbulence affected the mean flow.
In particular we need expressions for the Reynolds stresses. For a turbulence model to be useful
it must have wide applicability, be accurate, simple, and economical to run.
Common turbulence models based on Reynolds Averaged Navier-Stokes (RANS) equations
(time averaged):
1. Zero equation models: mixing length model.
2. One equation model: Spalart-Almaras.
3. Two equation models: k-ε style models (standard, RNG, realizable), k-ω model, and
ASM.
4. Seven equation model: Reynolds stress model.
The number of equations denotes the number of additional PDEs that are being solved.
2.2.1 Mixing Length Model
On dimensional grounds one can express the kinematic turbulent viscosity as the product of a
velocity scale and a length scale If we then assume that the velocity scale is proportional to the
length scale and the gradients in the velocity (shear rate, which has dimension 1/s) we can derive
Prandtl’s (1925) mixing length model Algebraic expressions exist for the mixing length for
simple 2-D flows, such as pipe and channel flow.
2.3 Spalart-Allmaras One-Equation Model
Solves a single conservation equation (PDE) for the turbulent viscosity. This conservation
equation contains convective and diffusive transport terms, as well as expressions for the
production and dissipation of νt Developed for use in unstructured codes in the aerospace

industry. Economical and accurate for: Attached wall-bounded flows and Flows with mild
separation and recirculation. Weak for: Massively separated flows, free shear flows and Decaying
turbulence.
2.3.1 K-Ε Model Discussion
Advantages
Relatively simple to implement.
Leads to stable calculations that converge relatively easily.
Reasonable predictions for many flows.
Disadvantages
Poor predictions for:
swirling and rotating flows,
flows with strong separation,
ax symmetric jets,
Certain unconfined flows, and
Fully developed flows in non-circular ducts.
2.3.2 Improvement: RNG k- ε
k-ε equations are derived from the application of a rigorous statistical technique (Renormalization
Group Method) to the instantaneous Navier-Stokes equations. Similar in form to the standard k-
ε equations but includes
• Additional term in ε equation for interaction between turbulence dissipation and mean
shear.
• The effect of swirl on turbulence.
• Analytical formula for turbulent Prandtl number.
• Differential formula for effective viscosity.
Improved predictions for:
• High streamline curvature and strain rate.
• Transitional flows.
• Wall heat and mass transfer.
But still does not predict the spreading of a round jet correctly.
2.3.3 Improvement: realizable k-ε
• Shares the same turbulent kinetic energy equation as the standard k-ε model.
• Improved equation for ε.
• Variable Cµ instead of constant.
• Improved performance for flows involving
• Planar and round jets (predicts round jet spreading correctly).
• Boundary layers under strong adverse pressure gradients or separation.
• Rotation, recirculation.
• Strong streamline curvature.

2.3.4 k-ω model
This is another two equation model. In this model ω is an inverse time scale that is associated
with the turbulence. This model solves two additional PDEs
• A modified version of the k equation used in the k-ε model.
• A transport equation for ω.
The turbulent viscosity is then calculated as follows
• Its numerical behavior is similar to that of the k-ε models.
• It suffers from some of the same drawbacks, such as the assumption that µtis isotropic.
2.3.5 Algebraic Stress Model
The same k and ε equations are solved as with the standard k-ε model. However, the Boussinesq
assumption is not used. The full Reynolds stress equations are first derived, and then some
simplifying assumptions are made that allow the derivation of algebraic equations for the
Reynolds stresses. Thus fewer PDEs have to be solved than with the full RSM and it is much
easier to implement. The algebraic equations themselves are not very stable, however, and
computer time is significantly more than with the standard k-ε model. This model was used in
the 1980s and early 1990s. Research continues but this model is rarely used in industry anymore
now that most commercial CFD codes have full RSM implementations available.
2.3.6 Reynolds Stress Model
RSM closes the Reynolds-Averaged Navier-Stokes equations by solving additional transport
equations for the six independent Reynolds stresses. Transport equations derived by Reynolds
averaging the product of the momentum equations with a fluctuating property. Closure also
requires one equation for turbulent dissipation. Isotropic eddy viscosity assumption is avoided.
• Resulting equations contain terms that need to be modeled.
• RSM is good for accurately predicting complex flows.
• Cyclone flows, swirling combustor flows.
• Rotating flow passages, secondary flows.
• Flows involving separation.
2.3.7 Large Eddy Simulation
Large eddy simulation (LES) is a mathematical model for turbulence used in computational. It
was initially proposed in 1963 by Joseph Smagorinsky to simulate atmospheric air currents and
many of the issues unique to LES were first explored by Deardorff (1970) LES grew rapidly and
is currently applied in a wide variety of engineering applications, including combustion,
acoustics, and simulations of the atmospheric boundary layer. LES operates on the Navier-Stokes
equations to reduce the range of length scales of the solution, reducing the computational cost.
The principal operation in large eddy simulation is low-pass filtering. This operation is
applied to the Navier-Stokes equations to eliminate small scales of the solution. This reduces the
computational cost of the simulation. The governing equations are thus transformed, and the
solution is a filtered velocity field. Which of the "small" length and time scales to eliminate are
selected according to turbulence theory and available computational resources.
Large eddy simulation resolves large scales of the flow field solution allowing better fidelity
than alternative approaches such as Reynolds-averaged Navier-Stokes (RANS) methods[11-13].
It also models the smallest (and most expensive) scales of the solution, rather than resolving them
as direct numerical simulation (DNS) does. This makes the computational cost for practical

engineering systems with complex geometry or flow configurations, such as turbulent jets,
pumps, vehicles, and landing gear, attainable using supercomputers. In contrast, direct numerical
simulation, which resolves every scale of the solution, is prohibitively expensive for nearly all
systems with complex geometry or flow configurations.
2.3.8 Direct Numerical Simulation
A direct numerical simulation (DNS) is a simulation in computational fluid dynamics in which
the Navier-Stokes equations are numerically solved without any turbulence model. This means
that the whole range of spatial and temporal scales of the turbulence must be resolved [8-10]. All
the spatial scales of the turbulence must be resolved in the computational mesh, from the smallest
dissipative scales (Kolmogorov micro scales), up to the integral scale L, associated with the
motions containing most of the kinetic energy.
2.4 CFD Optimization And Mesh Generation
The main process of this project is to create an geometry of the required model to be analysed.
The following steps are been involved in this process Geometry generation, Cleanup Mesh
generation. Different steps of mesh generation is shown in Fig. 2,3. Various grid types can be
generated in an automated or manual way: Pure hexahedral mesh,Tetrahedral / hybrid mesh, Hex-
dominant grids (combination of hexa and tetra elements) The following model is been developed
by using the latest commercial software tool ICEM CFD.The required model geometry has been
created by using the latest software and is been hexa meshed by using the features of the
commercial software
Figure 2 Wireframe of Mesh Generated.

Figure 3 Mesh around The Bluff.
2.5 Analysis Parameters
The various analysis parameters used are shown in table 1.
2.5.1 Reynolds Number
The flow pattern of the swirl jet has been studied in the near vicinity of the jet exit for three
different inlet annular Reynolds numbers namely 21000, 29000, and 37000. These
Reynolds numbers are selected because of the following reasons:
• For higher Reynolds number in the order of 105
, there is no appreciable effect of
rotation of the cylindrical disc in the flow field.
• In many of the literature it is seen that the experiments were conducted for Reynolds
numbers in the order of 104
to get a beneficial recirculation zone.
• Because of the insensitivity to low dynamic pressure of the pitot tube, the error
involved in calibrating the regions of low velocity below approximately 2 m/s is high.
It happens in the recirculation zone when the Reynolds number in the order of 103
is
used.
2.5.2 Swirl Angle
The swirler design is almost the same as that of the one used by Shi and Chehroudi (1994) which
was used to produce the widest stable flame region. The swirlers with 0, 15, and 30degree slots
were used for the experiment. This includes the one (30 degree) which is similar to what is
employed in industrial furnaces and burners [2].
2.5.3 Speed of Rotation of the Cylindrical Disc
As the main aim of the whole project is to understand the effect of rotation of the cylindrical disc
on the flow field and in order to make correlations of the speed of rotation with the other flow
parameters, experiments were conducted for three speeds namely 0 and 9000 rpm.
Direction of Rotation of the Cylindrical Disc
It is intended to see the difference imparted in the flow field due to the direction of rotation
of the cylindrical disc. Facing the wind tunnel exit, the swirl plate generates a clockwise swirling
flow. By rotating the cylindrical disc in clockwise direction i.e., in the same direction of the swirl,
a co-rotation is made. By rotating it in the opposite direction of the swirl direction, a counter-

rotation is made. Hence, in this thesis clockwise rotation (CW) means co-rotation and
counterclockwise rotation (CCW) means counter-rotation.
2.5.4 Blockage Ratio
Blockage ratio is defined as the ratio of the blockage area of the bluff-body to the cross-sectional
area of the outer pipe. The experiment is conducted for a bluff body of diameter d=50 mm; the
diameter of the outer pipe is D=100 mm. Therefore, the blockage ratio is 0.25.
Table 1. Analysis Parameters
Blockage ratio 0.25
Reynolds number 21000,29000,37000
Speed of rotation of the cylindrical disc 0,9500 rpm
Direction of rotation of the cylindrical disc
Co and Counter rotation
with the swirl direction
2.6 Results and Discussion
Table 2. Length of recirculation Zone
Blockage Ratio Swirl Angle No Rotation
Co-Rotation
9500rpm
25
0
0.029 Closed
toroid
0.029 Closed
toroid
30
0.0185 Closed
toroid
0.0625
Open
toroid
45
0.1215
Open
toroid
0.1765
Open
toroid
Table 2 represents the length of recirculation zone for various cases. Generally increases the
swirl number, the length of the recirculation is increased. In this chart counter rotation
recirculation is higher compared to the other because in the counter rotation, swirl number is high
compared to co rotation and no rotation cases.
2.6.1 Review of Recirculation Zone
The recirculation zone represents that is directly proportional to the swirl number for no rotation
case. Also that is noted that the rate of change of recirculation increases with increasing swirl
number whereas in the counter rotation case the vice versa.conversly, the co rotation case is
showing an increasingly swirl number which means the stretching of the recirculation bubble.
2.6.2 Results Analyzed
Here in our part of analysis of fluid flow we have taken two cases in our model that are the no
rotation and the rotation of the cylinder bluff. Here we now discuss the various parameters that
are analyzed by using the commercial software called FLUENT. The various parameters that we
are taken into account are static pressure, total pressure and the axial velocity.

2.6.3 With No Rotation
Figure 4 Static Pressure At Initial Stage
Figure 5 Static Pressure At Final Stage
Figure 6 Velocity Magnitude AtInitail Stage

Figure 7 Velocity Magnitude At Final Stage
Figure 8. Axial Velocity At Initial Stage
Figure 9 Axial Velocity At Final Stage

Figure 10 Axial Velocity Of Total Model
Figure 11 Axial Velocity At The Blockage
Figure 12 Total Pressure

Figure 13 Static Pressure
The above shown diagrams from fig.4 to fig. 13 are belongs to the no rotation of the blockage
cylinder placed in the turbulent jet. The results that are displayed here bought from the
commercial software FLUENT and the animated diagrams are been captured with the help of the
CFD-POST.
2.6.4 with Rotation
The following figures from fig. 14 to fig. 23 shows the blockage with the rotation of the
turbulent jet.
Figure 14. Static Pressure at Initial Stage

Figure 15 Static Pressure At Final Stage
Figure 16 Velocity Magnitude At Initial Stage
Figure 17 Velocity Magnitude At Final Stage

Figure 18 Axial Velocity At Initial Stage
Figure 19 Axial Velocity At Final Stage
Figure 20 Static Pressure

Figure 21 Total Pressure
Figure 22 Axial Velocity Of Total Model
Figure 23 Axial Velocity at Blockage
2.7 CONCLUSION
The swirl flow favors the recirculation region. The burner there by enchasing the flame stability
and length and also reduced the flame area. This work is initiate by a global approach with respect
to the influence of integrating the swirl burners in compact field heating units. The outcome of
the study state that the use of swirl burners in small confinement allows for low NOX,high
efficiency and high compact units.

Effects of no rotation and rotation
• The spread increases with the increase of the swirl number, thus the entrainment also
increases with the swirl.
• The recirculation length is directly proportional to the swirl number and the rate of
change of increases with increasing swirl number.
Thus here in this work the rotation is showing the beneficial effect of forming a closed toroidal
structure with a stagnation point on the axis even for smaller swirler. The stagnation point is one
of the critical factors in flame stabilization.
REFERENCES
[1] Adi Surjosatyo and Farid Nasir Ani(2011) ,’Study of Enhancing the Swirl Burner
Performance On a Small scale Biomass Gasification’, International Journal of Engineering
& Technology IJET-IJENS ,11, pp. 21-38.
[2] Adi Surjosatyo* and Yudho Danu Priambodho(2011),’Investigation Of Gas Swirl burner
Characteristic On Biomass Gasification system’,JurnalMekanikal,33,pp.15-31.
[3] Chen, R. H., and Driscoll, J. F.’ “The Rule of the Recirculation Vortex in Improving Fuel-Air
Mixing within Swirling Flames’, Twenty-Second Symposium (International) on Combustion,
Combustion Institute, Pittsburgh(1988) ,pp. 531- 440.
[4] Dellenback, P.A., Sanger, J.L. and Metzger, D.E. (1994) ,’Heat transfer in coaxial jet mixing
with swirled inner jet,ASME J. Heat Transfer, 116, pp. 864-870
[5] Kang D M a, F.E.C. Culick a, A. Ratner b(2007),’ Combustion dynamics of a low-swirl
combustor’, Combustion and Flame,151,pp.412-425.
[6] Manuel GarcVillalba, JochenFrÄohlich and Wolfgang Rodi,’ Large Eddy simulation Of An
Annular Swirling Jet With Pulsating Inflow’, University of Karlsruhe,Germany.
[7] Martin Habermehl, Jens Erfurth, Dobrin Toporov, Malte Förster, Reinhold Kneer(2011),’
Experimental and numerical investigations on a swirl oxycoal Flame’ ,Applied thermal
enginenering,pp.1-9.
[8] Maria Grazia DeGiorgi, AldebaraSciolti, StefanoCapilongo, AntonioFicarella, ‘Experimental
and numerical investigations on the effect of different air-fuel mixing strategies on the
performance of a lean liquid fueled swirled Comustor.’ Energy Procedia,101, November
2016, Pages 925-932
[9] Syred N and J.M. Beer, Combustion in Swirling Flow: A Review, Combustion and Flame23
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[10] StevanNemoda,VukmanBakic, Simeon Oka, Goran Zivkovic,NenadCrnomarkovic(2005),
‘Experimental and numerical investigation of gaseous fuel combustion in swirl chamber’,
International Journal of Heat and Mass transfer, 48,pp. 4623–4632.
[11] Yang Yang(2010),’ Large Eddy Simulation Of Sydney Swirl Non-Reaction Jets’, Department
of Energy TechnologyAalborg University.
[12] Yehia A. Eldrainy a, Khalid M. Saqr b, Hossam S. Aly a, Mohammad
NazriMohdJaafar(2009),’ CFD insight of the flow dynamics in a novel swirler for gas turbine
combustors’, International Communications in Heat and Mass transfer,36,pp.936-941.
[13] Ying Huang*, Vigor Yang(2005),’ Effect of swirl on combustion dynamics in a lean-
premixed swirl-stabilized combustor’, Proceedings of the Combustion Institute,30,pp. 1775–
1782.

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