1. 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

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