The aerodynamic flow over a sedan class car is studied and the various parameters plotted. The coefficient of drag is calculated from the analysis

1. STUDY OF AERODYNAMIC
FLOW OVER A SEDAN CAR
JJ TECHNICAL SOLUTIONS
(www.mechieprojects.com)

2. AIM
1. To study and understand the aerodynamic air flow over a sedan class car using CFD
2. To calculate the aero-force acting on the vehicle for different velocities & compute the drag
coefficient

3. PROBLEM FORMULATION
Tools Used:
1. Drafting/Modeling: SolidWorks
2. Meshing: Gambit
3. Analysis & Post Processing: Fluent
Car
Velocity Inlet
Meshing of Model in Gambit & Defining Boundary Conditions
Pressure Outlet
Velocity Inlet
Wall
Velocity of Car
Considered
1. 10m/s
2. 15m/s
3. 20m/s
4. 30m/s
5. 40m/s
6. 50m/s
7. 60m/s

4. Problem Definition in FLUENT
Define
the
problem
as,
— Solver
-­‐Pressure
based
— Formulation
-­‐Implicit
— Space
-­‐2D
— Time
-­‐Steady
— Viscous
-­‐Two-­‐equation
SST-­‐k-­‐omega
model
— Enable
the
Energy
equation
— The
fluid
type
used
is
Air
defined
as
ideal
gas
— Operating
pressure=
0
Pa

5. LIFT, DRAG, AND MOMENT COEFFICIENTS
• Behavior of L, D, and M depend on α, but also on velocity and altitude
• V∞, ρ ∞, Wing Area (S), Wing Shape, µ ∞, compressibility
• Characterize behavior of L, D, M with coefficients (cl, cd, cm)
( )Re,,
2
1
2
1
3
2
2
∞
∞
∞
∞
=
=≡
=
Mfc
Scq
L
ScV
M
c
SccVM
m
m
m
α
ρ
ρ
( )Re,,
2
1
2
1
2
2
2
∞
∞
∞
∞
=
=≡
=
Mfc
Sq
D
SV
D
c
ScVD
d
d
d
α
ρ
ρ
( )Re,,
2
1
2
1
1
2
2
∞
∞
∞
∞
=
=≡
=
Mfc
Sq
L
SV
L
c
ScVL
l
l
l
α
ρ
ρ
Note on Notation:
We use lower case, cl, cd, and cm for infinite wings (airfoils)
We use upper case, CL, CD, and CM for finite wings

6. PRESSURE COEFFICIENT, CP
• Use non-dimensional description, instead of plotting actual values of pressure
• Pressure distribution in aerodynamic literature often given as Cp
• So why do we care?
– Distribution of Cp leads to value of cl
– Easy to get pressure data in wind tunnels
– Shows effect of M∞ on cl
2
2
1
∞∞
∞
∞
∞ −
=
−
≡
V
pp
q
pp
Cp
ρ

7. Contours of Static Pressure around the Car for Car Velocity =10m/s

8. Contours of Pressure Coeff. around the Car for Car Velocity =10m/s

9. Contours of Total Pressure around the Car for Car Velocity =10m/s

10. Contours of X-dir. Velocity around the Car for Car Velocity =10m/s

11. Contours of Turbulent viscosity around the Car for Car Velocity =10m/s

12. Contours of Velocity magnitude around the Car for Car Velocity =10m/s

13. Pressure coeff. Plot on top & bottom of the Car for Car Velocity =10m/s

14. Contours of X-dir. Velocity at the front of the Car for Car Velocity =10m/s

15. Contours of X-dir. Velocity at the front of the Car for Car Velocity =10m/s

16. Contours of X-dir. Velocity at the rear of the Car for Car Velocity =10m/s

17. Contours of Stream Function around the Car for Car Velocity =10m/s

18. Velocity Vectors around the Car for Car Velocity =10m/s

19. Contours of X. dir. Velocity around the Car for Car Velocity =60m/s

20. Contours of Turbulent Intensity around the Car for Car Velocity =60m/s

21. Vehicle
Velocity
(m/s)
Pressure
Force(N)
Viscous
Force(N)
Total
Force (N)
Pressure
Coeff.
Viscous
Coeff.
Total
Coeff. Cl Cd
10 34.071352 4.4314715 38.502823 0.2317779 0.0301460 0.26192396 -1.48 0.262
15 74.373342 9.298441 83.671783 0.2248627 0.0281131 0.2529759 -1.64 0.253
20 130.07131 15.765496 145.83681 0.2212097 0.0268120 0.24802177 -1.75 0.248
30 288.49465 33.227231 321.72188 0.21806095 0.0251150 0.24317601 -1.92 0.243
40 508.64031 56.428935 565.06924 0.21625863 0.0239918 0.24025052 -2.03 0.240
50 790.09973 85.12556 875.22529 0.21499312 0.0231634 0.23815653 -2.10 0.238
60 1137.7129 119.11565 1256.8286 0.21498731 0.0225086 0.23749594 -2.18 0.238
RESULTS

24. CONCLUSION
1. The contours of Velocity, Pressure & Turbulence is plotted, around
the sedan car and studied for car velocity changing from 10 - 60m/s.
2. The velocity increases neat the hood of the car and the pressure
decreases
3. A swirl/ backflow is generated at the rear end of the car with
negative velocity.
4. The pressure coefficient is plotted for the top & bottom side of the
car.
5. The pressure force, viscous force and total force acting on the car
for different velocities is plotted against car velocity.
6. The viscous force is a small fraction of total force acting on the car.
7. The Lift coefficient decreases with the increase in car velocity,
8. The Drag coefficient (Cd) for the car is = 0.24

25. FOR COMPLETE PRESENTATION, MORE PROJECTS
PRESENTATIONS AND PROJECT REPORTS VISIT
WWW.MECHIEPROJECTS.COM
Email: contactus@mechieprojects.com
THANKYOU