1. Computer Simulation of Vehicle Aerodynamic Forces and Moments Using Fluent MSC VisualNastran 4D WorkingModel 2D
Zerguy Maazouddin
California State University Sacramento
ME 143 – Vehicle Design
Professor Jose J. Granda
Fall 2006

2. Introduction WorkingModel 2D Simulation
Introduction to Fluent 6.2 and Gambit 2.2
Ahmed Vehicle Model
Aerodynamic Influence of the Rear End Inclination Angle and Rear End Shape
1989 Ford Escort
Wind Tunnel Test Simulation
Compare the Wind Tunnel Test Results to:
ME 143 Course Text: Theory of Ground Vehicle 3rd Edition, J.Y. Wong
MSC VisualNastran4d Simulation
Escort’s Dynamics when the Front Lift Force > Rear Lift Force
WorkingModel 2D Simulation

3. Fluent 6.2 / Gambit 2.2
Fluent 6.2 and Gambit 2.2 Are Used to Create Computational Fluid Dynamics (CFD) Simulations
ME 296 – Course on Fluent and Gambit
Fluent and Gambit located in RVR 4001
Tutorials Available
Gambit 2.2
Create the Model’s Geometry
Create the Model’s Mesh
Set Boundary Conditions
Export Your Gambit File to Fluent for CFD Simulation
You Are Able to Import Geometry from SolidWorks, ProEngineer, and AutoCAD
Fluent 6.2
Define Model’s Solver, Energy Equation, Laminar / Turbulent Flow
Set the Material’s Physical Valve – Fluid or Solid
Define the Boundary Conditions
Run Simulation
Mathematical Equations, Assumptions, Physical Parameters, etc… can be found in the Fluent Documentation located in RVR 4001

4. Fluent 6.2 Examples Fluid Flow Over a Military Aircraft
Fluid Flow Over a Car Tire
Space Aircraft Entry Into Mars
Fluid Flow Over an SUV

5. Ahmed Vehicle Model
Ahmed Vehicle Model Was Used to Study Vehicle Aerodynamics
Experimental Wind Tunnel Test
CFD Simulation Wind Tunnel Test
Aerodynamic Influence of the Rear End Inclination Angle and Rear End Shape Was Studied

6. Ahmed Vehicle Model - Rear End Inclination Angle Results Show That as The Angle Increases The Aerodynamic Drag Increases F. Chometon1
12 deg
20 deg
30 deg
12 deg
20 deg
30 deg

7. Ahmed Vehicle Model - Rear End Shape Results Show That Adding a Rear End Deck, Spoiler, and New End Spoiler The Aerodynamic Drag Decreases. It Should Be Noted That In Some Cases Adding A Spoiler Will Cause The Front Drag Lift Force to Become Greater Than The Rear Drag Lift Force; Causing The Vehicle To Rollover. H. Fukuda2
20 deg
20 deg
20 deg
20 deg
20 deg
20 deg

8. 1989 Ford Escort Wind Tunnel Test Simulation
Create 2D Model in Gambit
Create the Model’s Geometry
Create the Model’s Mesh
Set Boundary Conditions
Export the Gambit File to Fluent for CFD Simulation
You Are Able to Import Geometry from SolidWorks, ProEngineer, and AutoCAD
Setup Simulation in Fluent
Define Solver, Energy Equation, Laminar / Turbulent Flow
Set Material Values – Fluid / Solid
Set Order of Equations
Monitor Physical Parameters
Run Simulation
Results
SolidWorks Model

9. 1989 Ford Escort – Gambit Geometry  Vertices

10. 1989 Ford Escort- Gambit Geometry  Edges

11. 1989 Ford Escort – Gambit Geometry  Faces

12. 1989 Ford Escort – Gambit Wind Tunnel  Same Procedure

13. 1989 Ford Escort – Gambit Wind Tunnel  Subtract Flow Face From Escort Face

14. 1989 Ford Escort – Gambit Mesh  Grading – Edit, Defaults, Edge, Flexible Grading, Set to 1

15. 1989 Ford Escort – Gambit Mesh  Face, Tri, 0.08 Interval Size

16. 1989 Ford Escort – Gambit Mesh  Face, Tri, 0.08 Interval Size

17. 1989 Ford Escort – Gambit Set Boundary Conditions – Flow Face

18. 1989 Ford Escort – Gambit Set Boundary Conditions – Escort Face
Save File
File  Export  Mesh

19. 1989 Ford Escort – Fluent File  Read Mesh  Display  Grid

20. 1989 Ford Escort – Fluent Solver / Viscous Model
2D Steady State
Viscous Model
Turbulent : k-epsilon
Re = 4 x 106

21. 1989 Ford Escort – Fluent Material – Fluid – Air / Operating Conditions
Pressure Constant = 0
Temp = 20 C
Re = Vel x Model Height / viscosity
Vel = 60 m/s
Model Height = 1.09 m

22. 1989 Ford Escort – Fluent Boundary Conditions  Fluid - Air

23. 1989 Ford Escort – Fluent Boundary Conditions  Vel Inlet / Pressure Outlet

24. 1989 Ford Escort – Fluent Solution Controls
1st Order Equations
First Order Upwind
Approx 300 Iterations till Convergence
2nd Order Equations
Second Order Upwind
Approx 800 Iterations till Convergence

25. 1989 Ford Escort – Fluent Initialize / Equation Monitors / Run Simulation

26. 1989 Ford Escort – Fluent Results - Monitors
These Graphs Show That The Simulation’s Mathematical Equations Converged

27. 1989 Ford Escort – Fluent Results – Velocity Contour

28. 1989 Ford Escort – Fluent Results – Static Pressure

29. 1989 Ford Escort – Fluent Results – Influence of Spoiler

30. 1989 Ford Escort-Fluent-Results-Influence of Spoiler Results Show That Adding a Spoiler Will Reduce The Aerodynamic Drag

31. 1989 Ford Escort – Fluent Results – Aerodynamics Forces and Moments

32. Theory of Ground Vehicles 3rd Edition, J.Y. Wong
1989 Ford Escort – Fluent Results – Coefficient of Drag, Front Lift, and Rear Lift. Also, Rolling Moment and Yawing Moment
2D Escort Model CD
CLF
CLR
Rm (Nm)
Ym (Nm)
Original Shape
0.49
0.03
0.38
-2559
-2413
Spoiler Shape
0.46
0.02
0.33
-1900
Theory of Ground Vehicles 3rd Edition, J.Y. Wong CD
Table 3.1
Page 214
Ford Escort 1.3 GL
Total Body Drag
0.28
Table 3.2
Page 222

33. MSC VisualNastran 4D Front Drag Lift Simulation
VisualNastran4d Simulation
Front Drag Lift Simulation
Impulse Results
Click On Image to Start Video

34. MSC VisualNastran 4D Front Drag Lift Simulation
Results: Fluent Calculated the Rear Drag Lift to be Approx 891N.
Therefore, to Simulate the Vehicle’s Front From Lifting Off The Road
The Front Drag Lift Needs to Be Greater Than 891N. VisualNastran 4D Calculated this Force to be
3x105 N.
Click On Image to Start Video
VisualNastran 4D Calculated That the Impulse Force Between the Escort’s Body and Road will
Be a Maximum 200,000 (kg m)/s

35. WorkingModel 2D Front Drag Lift Simulation
WorkingModel 2D Simulation
Front Drag Lift Simulation
Total Force Results
Total Force Approx = 7000N

36. WorkingModel 2D Front Drag Lift Simulation
WorkingModel 2D Calculated That the Total Force Between the Escort’s Body and Road will
Be Approx 7000N

37. References
1. Chometon, F., Gillieron, P. “Modelling of Stationary Three-Dimensional Separated Air Flows around an Ahmed Reference Model”.Third International Workshop on Vortex Flows and Related Numerical Methods. Vol. 7, 1999,
2. Fukuda, H., Yanagimoto, K., China, H., “Improvement of vehicle aerodynamics by wake control”. Society of Automotive Engineers of Japan. Vol 16 (1995)
3. Franck, G., D’Elia, J., “CFD modeling of the flow around the Ahmed vehicle model”
Gillespie, T Fundamentals of Vehicle Dynamics. Society of Automotive Engineers, Inc. 1992
Wong, J.Y. Theory of Ground Vehicles 3rd Edition. John Wiley & Sons, Inc. 2001

38. Conclusion Design of Vehicles Questions Aerodynamics – Fluent
Design – SoildWorks
FEA – Patran
Dynamic Analysis – VisualNastran4d
In-depth Analysis – MSC Adams
Questions