1. Flow interaction between two Cars in windtunnel and in Environment By: Ahmad Gohari Farhad Jebelisinaki 1

2. Introduction We investigate in this Project: - The air flow modification induced by two cars driving behind each other in a line - It is well-known depending on speed and distance, between two cars there would be a strong interaction 2

3. Consideration Distance between two cars is 3 meters We investigate the cars in a wind tunnel of 70 km/h and 140 km/h of air speed at inlet velocity We will solve the problem with first and second order equation and compare them with together Consideration: Steady state-two dimensional-two identical cars-turbulent flow-compresible air flow 3

4. Geometry and mesh Length of windtunnel: 50 meters Height of windtinnel: 10 meter we consider enough space in front and in the back of the cars 4

5. Mesh Quality test 95.6% of mesh are equi-size 94.2% equi-angle 5

6. Defining boundary condition in Gambit We defined the boundary conditions in Gambit as: Velocity inlet Outflow Walls Interior (which is just a line to make the meshing easy) 6

7. Fluent adapt boundary mesh by Fluent 7

8. Results for speed of 70 km/h Model of simulation: first order Contour of velocity and Pressure 8 Velocity contoue Pressure contour

9. Model of simulation: first order force report 9 70 km/h 140 km/h

10. Fleunt modeling order: second order 70 km/h 140 km/h 10

11. Force report second order 11 70 km/h 140 km/h

12. Now we investigate the cars in a windtunnel with height of 3.5 meters and compare the results distance between cars 3 meters speed 70 km/h 12 Force report

13. Now we investigate the cars in a windtunnel with height of 3.5 meters and compare the results distance between cars 3 meters speed: 140 km/h 13

14. Consideration in Enviroment We had investigated the air-flow for two Cars in a windtunnel. Now we want to simulate the cars in real environment. For this case we would have no velocity inlet (air is at rest in environment) and we would define the velocity of 70 and 140 km/h for two cars. And compare them together. In this case there would be boundary condition of 1 bar at inletflow and outflow 14

15. Distance between cars: 3 meters Cars are moving in environment 15 Force report

16. When force interaction between cars become negligible? (70 km/h) In this case we investigate the force interaction between two cars for 10,20,30,40 meters and compare the force changing in these distances. Height of windtunnel: 10 meters 16

17. When force interaction between cars become negligible? (70 km/h) 17

18. When force inteaction between cars become negligible? (140 km/h) 18

19. In the distance of 40 we can consider the force difference can be negligible, indeed there’s no interaction between cars speed: 70 km/h 19

20. In the distance of 40 we can consider the force difference can be negligible, indeed there’s no interaction between cars speed: 140 km/h 20

21. Conclusion Speed is higher in sharp angels and pressure is lower in sharp angels and inverse Viscous force are much less than Pressure forces on the cars Total pressure on first car is more than the second car After 40meters body force interaction between cars is negligible If speed increases, body force on Cars and air-flow interaction between cars will increase A Windtunnel with less height can effect the amount of velocity,pressure and body forces on Cars, the amount of body forces will increase in a Windtunnel with less height. 21