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

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

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

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

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

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

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

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

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

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

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

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

Separation with and without actuation Fluid Mechanics Laboratory University of Kentucky

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

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

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

Questions? Fluid Mechanics Laboratory University of Kentucky