1. Drag reduction of a Ahmed body using pulsed jets International Forum of Flow Control (IFFC – 2)
P. JOSEPH
Institut AéroTechnique (IAT)
CNAM, France
X. AMANDOLESE
Aerodynamics Department
CNAM, France
J-L. AIDER
PMMH Laboratory
UMR 7636 CNRS
ESPCI ParisTech, France
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

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. Measurements localization
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. Total pressure loss coefficient (Cpi)
Reference results
Wake measurements
Re = 1,4 x 106
144 mm behind model
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. Strouhal (Slant height based) – 20 m/s
Reference results
Unsteady measurements in wake (Kiel and hot wire)
Location
Frequency (Hz) – 20 m/s
Strouhal (Slant height based) – 20 m/s
32 Hz
0,15
140 Hz
0,66

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. Continious line – slant top edge Broken line – slant top edge
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 Influence on the local pressure – slant surface Drag
Upper slant surface pressure
Broken line – roof end
Winglets– roof end
Broken line – roof end
Winglets– 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 Influence on the local pressure – vertical surface
Drag
Vertical surface pressure
Broken line – roof end
Winglets– roof end
Broken line – roof end
Winglets– 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.
Setup
Drag reduction
(%)
Frequency
(Hz)
St.
(slant height based)
Jet Speed
(m/s)
Broken line – roof
7,8
140
0,66 77
Continious line – slant edge
7,5 75
0,35 22
Broken line – slant edge
6,3
260
1,22 41
Winglets – roof
6,9
240
1,13

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.