Drag reduction of a Ahmed body using pulsed jets International Forum of Flow Control (IFFC – 2)

1. Drag reduction of a Ahmed body using pulsed jetsInternational Forum of Flow Control (IFFC – 2) P. JOSEPH Institut AéroTechnique (IAT) CNAM, France pierric.joseph@cnam.fr X. AMANDOLESE Aerodynamics Department CNAM, France xavier.amandolese@cnam.fr J-L. AIDER PMMH Laboratory UMR 7636 CNRS ESPCI ParisTech, France aider@pmmh.espci.fr Acknowledgements : This work was carried out in the framework of a ANR research programme (CARAVAJE) supported by ADEME.

2. Introduction • CARAVAJE Project : • « Control of the external aerodynamics of automotive vehicles by pulsed jets » • Partnership between seven industrials and laboratories • Thematic ANR project financed by ADEME FLOWDIT Microtechnology and Fluid Mechanics www.flowdit.com

3. Summary • Experimental setup • Experimental measurements • Reference results • Pulsed jets actuation • Control results • Conclusion

4. Experimental setup • Reference Ahmed body model • Standard dimensions with 25° slant angle.

5. Experimental setup • S4 wind tunnel facility, at Institut AéroTechnique 5m x 3m cross section (turbulence  1% ; wind - speed up to 40 m/s). Raised floor with airfoil shaped leading edge.

6. Experimental measurements • Drag measurements • 6 components unsteady aerodynamic balance. • Precision < 0,5 %.

7. Experimental measurements • Wall measurements : • 127 pressures taps. • Surface oil flow visualisation.

8. Experimental measurements • Wake measurements : • 2,5D exploration device. • Various probes (hot wire, Kiel, 7 holes…).

9. Reference results • Boundary layers measurements – incoming flow δ = 25 mm H = 1,25

10. Reference results • Boundary layers measurements – incoming flow δ = 24 mm H = 1,21

11. Reference results • Drag results • Significant Reynolds effect. • Consistent with reference results ([Ahmed 1984] : Cx = 0,285 for Re ≈ 4,2 x 106).

12. Reference results • Wall pressure and visualisations measurements • Reynolds effect on the recirculation bubble and surface pressure distribution. Measurements localization Re = 1,4 x 106 Re = 2,1 x 106 Re = 2,8 x 106

13. Reference results Re = 1,4 x 106 144 mm behind model • Wake measurements Position of the measurements plan • Kiel probe measurements. • Flow structure consistent with classical Ahmed topology [Ahmed 1984]. With PTA the undisturbed flow total pressure and PTM the wake total pressure. Total pressure loss coefficient (Cpi)

14. Slant height Reference results • Unsteady measurements in wake (Kiel and hot wire)

15. Reference results • Unsteady measurements in wake (Kiel probe)

16. Reference results • Unsteady measurements in wake (Kiel probe)

17. Pulsed jets actuation • Control system description • Open loop system with solenoid valve : • Frequency from 5 Hz to 300 Hz. • Speed up to 80 m/s – 90 m/s (depends on exhaust geometry).

18. Pulsed jets actuation • Control system description Solenoid Valves (Matrix Ltd document). Component implantation inside Ahmed model. Jets exhaust (near slant edge).

19. Pulsed jets actuation • Control system location • 2 blowing locations : « roof end » and « slant top edge » • 3 exhaust geometries. Continous line Broken line Winglets

20. Control results • Influence of the forcing parameters on drag Broken line – roof end Winglets– roof end Jets Speed (m/s) Jets Speed (m/s) Frequency (Hz) Frequency (Hz) Continious line – slant top edge Broken line – slant top edge Jets Speed (m/s) Jets Speed (m/s) Frequency (Hz) Frequency (Hz) Drag reduction (%)

21. Control results • Influence on the local pressure – slant surface Sensor position

22. Control results Drag Upper slant surface pressure • Influence on the local pressure – slant surface Winglets– roof end Broken line – roof end Winglets– roof end Broken line – roof end Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Frequency (Hz) Frequency (Hz) Frequency (Hz) Frequency (Hz) Continious line – slant top edge Broken line – slant top edge Continious line – slant top edge Broken line – slant top edge Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Frequency (Hz) Frequency (Hz) Frequency (Hz) Frequency (Hz) Drag reduction (%) Pressure variation (%)

23. Control results Drag Vertical surface pressure • Influence on the local pressure – vertical surface Winglets– roof end Broken line – roof end Winglets– roof end Broken line – roof end Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Frequency (Hz) Frequency (Hz) Frequency (Hz) Frequency (Hz) Continious line – slant top edge Broken line – slant top edge Continious line – slant top edge Broken line – slant top edge Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Jets Speed (m/s) Frequency (Hz) Frequency (Hz) Frequency (Hz) Frequency (Hz) Drag reduction (%) Pressure variation (%)

24. Conclusion • Effective experimental setup. • Significants drag reduction. • Begining of comprehension of Cx reduction mecanisms.

25. Perspectives • Extensive parametric study : position, exhaust geometry, forcing parameters • Highlight the fluid - mechanisms involved by unsteady pression and flow analysis • Tests of MEMS actuators for better performance and efficiency.