This work deals with the drag estimation of a small shaped car using commercially available CFD softwares. The results are tabulated and plotted

1. STUDY OF AERODYNAMIC
FLOW OVER A NANO CAR
JJ TECHNICAL SOLUTIONS
(www.mechieprojects.com)
Photo Courtesy www.topspeed.in

2. AIM
1. To study and understand the aerodynamic air flow over a NANO 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. 2m/s
2. 5m/s
3. 10m/s
4. 15m/s
5. 20m/s
6. 25m/s
L2L 4L

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 a, but also on velocity and altitude
• V∞, r ∞, Wing Area (S), Wing Shape, m ∞, 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
a
r
r
 Re,,
2
1
2
1
2
2
2







Mfc
Sq
D
SV
D
c
ScVD
d
d
d
a
r
r
 Re,,
2
1
2
1
1
2
2







Mfc
Sq
L
SV
L
c
ScVL
l
l
l
a
r
r
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
r

11. Contours of Static Pressure around the Car for Car Velocity =2m/s

12. Contours of Dynamic Pressure around the Car for Car Velocity =2m/s

13. Contours of X velocity around the Car for Car Velocity =2m/s

14. Contours of X-dir. Velocity around the Car for Car Velocity =2 m/s

15. Velocity Vectors around the Car for Car Velocity =2 m/s

16. Contours of Velocity magnitude around the Car for Car Velocity =25m/s

17. Velocity Magnitude of the Car for Car Velocity =25m/s

18. Contours of X-dir. Velocity of the Car for Car Velocity =25m/s

19. Contours of Y-dir. Velocity of the Car for Car Velocity = 25 m/s

20. Contours of Static Pressure of the Car for Car Velocity =25m/s

21. Contours of Dynamic Pressure of the Car for Car Velocity =25m/s

22. Absolute Pressure Contours around the Car for Car Velocity =25m/s

23. Contours of Pressure Coeff. around the Car for Car Velocity = 25m/s

24. RESULTS
Vehicle
Velocity
(m/s)
Drag
coeff.
Cd
Lift
coeff.
Cl
Pressure
Force
(N)
Viscous
Force
(N)
Total
Force
(N)
Pressure
Coeff.
Viscous
Coeff.
Total
Coeff.
2
0.405 0.778 1.756 0.088 1.844 0.385 0.019 0.405
5
0.393 0.802 10.755 0.445 11.199 0.378 0.016 0.393
10
0.387 0.843 42.596 1.521 44.117 0.374 0.013 0.387
15
0.385 0.868 95.439 3.136 98.575 0.372 0.012 0.385
20
0.383 0.887 169.279 5.252 174.531 0.372 0.012 0.383
25
0.382 0.904 263.902 7.847 271.749 0.371 0.011 0.382

27. CONCLUSION
1. The contours of Velocity, Pressure & Turbulence is plotted, around
the sedan car and studied for car velocity changing from 2- 25m/s.
2. The velocity increases near 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 = 0.38

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29. This is purely an academic work and has no financial or other
interest.
The results achieved in this should be independently verified.