Experimental Closed Loop Control of Flow Separation on a Simple Hinged Flap

Transcription

1 Experimental Closed Loop Control of Flow Separation on a Simple Hinged Flap T. Chabert1, J. Dandois1, E. Garnier1 and L. Jacquin2 Onera, The French Aerospace Lab, Applied Aerodynamics Department 2 Fundamental and Experimental Aerodynamics Department 1 11/8/2013

2 Introduction Experimental set-up Synthesis of closed-loop control Closed-loop control of flow separation Introduction Applications of flow separation control on civil aircraft Simplification of flap deployment mechanisms Increase of rudder efficiency to reduce its size 2/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France. Conclusion

3 Wind tunnel and test model Eiffel-type wind tunnel ; velocities from 20 to 40 m.s 1 ; Re model 10 6 Seven actuator segments (Festo fast-switching valves) integrated into the flap along span Control of forcing frequency f + and momentum coefficient c μ 16 Senflex hot-films regularly chordwise distributed 51 wall pressure measurements (static) 3/17-11/8/ rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

4 Actuators : definition of c μ Steady momentum coefficient is defined after Poisson-Quinton (1948) as c μ = q m U j 1 2 ρ U 2 S 0 = ρ j U 2 j S j 1 2 ρ U 2 S 0, Oscillatory momentum coefficient (Greenblatt & Wygnanski, 2000) is defined as c μ = ρ j U 2 j S j 1 2 ρ U 2 S 0, For pulsed blowing, the jet velocity is (α is the duty cycle) U j (t) = Umax i 0 < t αt, 0 i αt < t T, So oscillatory momentum coefficient is c μ = α ρ j U 2 max S j 1 2 ρ U 2 S 0. (1) 4/17-11/8/ rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

5 Actuators : compressed air circuit Buffer tank sufficiently large (200 L) to dampen the oscillations due to the valves opening and closure A pressure regulator sets the pressure in the buffer tank to P f = 7 bar for all the experiments 5/17-11/8/ rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

6 Actuators : constant feeding pressure The pressure upstream from the valves is kept constant The jet velocity during the blowing phase of pulsed blowing case is equal to the jet velocity in the constant blowing case, so U max = U j and finally c μ = α c μ 6/17-11/8/ rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

7 Effect of duty cycle on flow separation Separated flow at δ = 20 and U = 24.5 m.s 1 Pulsed blowing duty cycle α = 10 (constant feeding pressure) 7/17-11/8/ rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

8 Effect of duty cycle on flow separation Separated flow at δ = 20 and U = 24.5 m.s 1 Pulsed blowing with duty cycle α = 50 (constant feeding pressure) 8/17-11/8/ rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

9 Effect of duty cycle on flow separation Wall pressure coefficient p distributions on the flap for increasing values of the duty cycle Duty cycle α has a direct effect on the flow separation that occurs on the flap Chosen to be the control variable 9/17-11/8/ rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

10 Estimation of flow separation location Typical time evolution of the detrended hot-film signals as function of chord position when the flow is excited by pulsed blowing (a) α = 25 (b) α = 25 The attached zone is organized around the perturbation that is induced by the periodic forcing The correlation coefficient map reveals how far the perturbation goes before dissipating 10/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

11 Estimation of flow separation location Correlation coefficient maps for different values of duty cycle α (c) α = 50 (d) α = 75 The limit between attached and separated zones is postponed to higher deflection angles Correlation coefficient reports the flow separation delay due to duty cycle increase 11/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

12 Steady-state response of the plant Definition of Δ = 12 i=1 [0.9 R xi x i+1 ] 2, where x i is the i th hot-film signal, with i }, and R xy the correlation coefficient Distance to reattachment Δ as function of the duty cycle α Distance Δ is reduced when the duty cycle increases Static map shows a plateau (since the flow cannot be more than fully reattached ) 12/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

13 Closed-loop control of c μ General scheme of closed-loop control Variations of duty cycle α = fast variations of c μ Variations of distance Δ = fast detection of flow separation 13/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

14 Closed-loop control of c μ Ariyur & Krstić (2004) extended extremum seeking control (Krstić & Wang, 2000) to general slope seeking control, more appropriate for plants whose static map exhibits a plateau Slope seeking control leads to full reattachment while keeping the duty cycle as low as possible 14/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

15 Proposed modification of slope seeking control If the deflection angle increases, α has to be increased in order to raise c μ If the deflection angle decreases, α has to be decreased to save power while maintaining the flow attached Fuzzy-logic regulator to raise the adaptation gain K FL from K 1 to K 2 (in absolute terms) when the local gradient is too low 15/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

16 Closed-loop control of c μ The slope-seeking algorithm is tested on the experiment ; δ is increased from 20 to 35 and then decreased from 35 to 20 ; U = 24.5 m.s 1 Constant gain Adaptive gain Implementation of an adaptive gain to compensate the lack of gradient in the high-to-low α direction : better convergence rate of duty cycle α when the deflection decreases 16/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.

17 Conclusions Oscillatory momentum coefficient depends on the compressed air circuit to feed the actuators constant feeding pressure : c μ = αc μ Oscillatory momentum coefficient c μ can be optimized to achieve flow reattachment using slope seeking Choice of duty cycle α as controlled variable (output) Choice of distance to reattachment Δ as indicator for flow separation (input) Improvement of slope seeking control by adapting the gain K in order to have the flow just reattached whatever the flap deflection is 17/17-11/8/2013-3rd GDR Symposium on Flow Separation Control, 7-8 November 2013, Lille, France.