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

Drag reduction of a Ahmed body using pulsed jets

International Forum of Flow Control (IFFC – 2)

P. JOSEPHInstitut AéroTechnique (IAT)

CNAM, [email protected]

X. AMANDOLESEAerodynamics Department

CNAM, [email protected]

J-L. AIDERPMMH LaboratoryUMR 7636 CNRS

ESPCI ParisTech, [email protected]

Acknowledgements :This work was carried out in the framework of a ANR

research programme (CARAVAJE) supported by ADEME.

Drag reduction of a Ahmed body using pulsed jets - IFFC-2 - Pierric JOSEPH

Introduction

2

• 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

FLOWDITMicrotechnology and Fluid Mechanicswww.flowdit.com


Summary

3

• Experimental setup

• Experimental measurements

• Reference results

• Pulsed jets actuation

• Control results

• Conclusion


Experimental setup

4

• Reference Ahmed body model

– Standard dimensions with 25° slant angle.


Experimental setup

5

• 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.


Experimental measurements

6

• Drag measurements

– 6 components unsteady aerodynamic balance.– Precision < 0,5 %.



7

• Wall measurements :

– 127 pressures taps.– Surface oil flow visualisation.



8

• Wake measurements :

– 2,5D exploration device.– Various probes (hot wire, Kiel, 7 holes…).


Reference results

9

• Boundary layers measurements – incoming flow

δ = 25 mm H = 1,25 δ = 25 mm H = 1,25


Reference results

10

• Boundary layers measurements – incoming flow

δ = 24 mm H = 1,21 δ = 24 mm H = 1,21


Reference results

11

• Drag results

– Significant Reynolds effect.– Consistent with reference results ([Ahmed 1984] : Cx = 0,285 for Re ≈

4,2 x 106).


Reference results

12

• 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


Reference results

13

• Wake measurements

Total pressure loss coefficient (Cpi)

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.

Re = 1,4 x 106

144 mm behind model


Reference results

14

• 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

32 Hz 0,15

32 Hz 0,15

140 Hz 0,66

Slantheight


Reference results

15

• Unsteady measurements in wake (Kiel probe)


Reference results

16

• Unsteady measurements in wake (Kiel probe)


Pulsed jets actuation

17

• 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

• Control system description

Solenoid Valves (Matrix Ltd document).

Component implantation inside Ahmed model.

Jets exhaust (near slant edge).



19

• Control system location

– 2 blowing locations : « roof end » and « slant top edge »– 3 exhaust geometries.

Continous line Broken line

Winglets


Control results

20

• Influence of the forcing parameters on drag

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Frequency (Hz) Frequency (Hz)

Frequency (Hz) Frequency (Hz)Drag reduction

(%)

Broken line – roof end Winglets– roof end

Continious line – slant top edge Broken line – slant top edge


Control results

21

• Influence on the local pressure – slant surface

Sensor position


Control results

22

• Influence on the local pressure – slant surface

Jets

Spe

ed (m

/s)

Frequency (Hz)

Drag reduction (%)



Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Frequency (Hz)



Frequency (Hz) Frequency (Hz)Pressure

variation (%)



Drag Upper slant surface pressure


Control results

23

• Influence on the local pressure – vertical surface

Jets

Spe

ed (m

/s)

Frequency (Hz)

Drag reduction (%)



Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Jets

Spe

ed (m

/s)

Frequency (Hz)



Frequency (Hz) Frequency (Hz)Pressure

variation (%)



Drag Vertical surface pressure


Conclusion

24

• Effective experimental setup.• Significants drag reduction.

• Begining of comprehension of Cx reduction mecanisms.

SetupDrag 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 75


Perspectives

25

• 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.

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

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