Low-Re Separation Control by Periodic Suction Surface Motion

1. Low-Re Separation Control by Periodic Suction Surface Motion David Munday, George Huang and Jamey Jacob Department of Mechanical Engineering University of Kentucky 19 November 2001 The 54th Annual Meeting of the Division of Fluid Dynamics American Physical Society Fluid Mechanics Laboratory University of Kentucky

2. Motivation • μAVs Re = 104 - 105 • UAVs Re = 105 - 106 • High Altitude • Other atmospheres (Mars) Fluid Mechanics Laboratory University of Kentucky

3. Laminar Separation Bubble • Adverse Pressure gradient on a laminar flow causes separation • Transition occurs. Fluid is entrained and turbulent flow re-attaches Figure from Lissaman Fluid Mechanics Laboratory University of Kentucky

4. Active Flow Control • Constant sucking or blowing • Intermittent sucking and blowing (synthetic jets) • Wygnanski, Glezer • Suggests existence of “sweet spots” in frequency range • Mechanical momentum transfer • Modi, V. J. • Change of the shape of the wing (Adaptive Airfoils) Fluid Mechanics Laboratory University of Kentucky

5. Adaptive Airfoils • Can change shape to adapt to flow • Simple examples: Flaps, Slats, Droops • Move slowly, quasi-static • Change shape parameter (usually camber) to adapt to differing flight regimes • Rapid Actuation • Can adapt to rapid changes in flow condition • May produce the same sort of “sweet spot” frequency response as synthetic jets Fluid Mechanics Laboratory University of Kentucky

6. Piezoelectric Actuation • Rapid actuation requires either large forces or light actuators • Piezo-actuators are small and light • They are a natural choice for μAV designs Fluid Mechanics Laboratory University of Kentucky

7. Adaptive Wing Construction • NACA 4415 • well measured, room for internal actuator placement • Modular (allows variation in aspect ratio) • Multiple independent actuators • Flexible insulating layer and skin Fluid Mechanics Laboratory University of Kentucky

8. Foil shape (mode shapes grossly exaggerated) Actual amplitude 0.002c Fluid Mechanics Laboratory University of Kentucky

9. Dynamic Model Flow Visualization • Flow Visualization is by the smoke wire technique • As described in Batill and Mueller (1981) • A wire doped with oil is stretched across the test section • The wire is heated by Joule heating and the oil evaporates making smoke trails • Limited to low Re • Limit due to requirement for laminar flow over wire • Limited to a wire diameter based Red < 50 Fluid Mechanics Laboratory University of Kentucky

10. Dynamic Model Flow Visualization α = 0˚ Actuator Fixed Actuation on Fluid Mechanics Laboratory University of Kentucky

11. Dynamic Model Flow Visualization α = 9˚ Actuator Fixed Actuation on Fluid Mechanics Laboratory University of Kentucky

12. Separation as a function of Reduced Frequency Fluid Mechanics Laboratory University of Kentucky

13. Separation with and without actuation Fluid Mechanics Laboratory University of Kentucky

14. Numerical Simulation • 2nd order backward temporal scheme • 3rd order QUICK spatial scheme • Chimera grid with moving overlapping grid capability, can handle moving boundaries • Parallel MPI Fluid Mechanics Laboratory University of Kentucky

15. Conclusions • Oscillation of the actuator has a pronounced effect on the size of the separated flow • Oscillation holds the separation at 70% to 4-6% of chord while un-actuated flow separates as much as 15% of chord • Separation can be reduced by from 30 to 60% relative to un-actuated flow-field Fluid Mechanics Laboratory University of Kentucky

16. Further Work • Expand the range of Re • Force measurements of Dynamic Mode • effect on L/D • PIV measurements of Dynamic Mode • flow control • Phase average PIV data • Comparisons with Numerical Simulation • Examine behavior with artificial turbulation • Compare gains in performance with power required Fluid Mechanics Laboratory University of Kentucky

17. Questions? Fluid Mechanics Laboratory University of Kentucky