fluid mechanics laboratory university of kentucky active control of separation on a wing with...
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Active Control of Separation on a Wing with Conformal Camber
David Munday and Jamey JacobDepartment of Mechanical Engineering
University of Kentucky8 January 2001
The 39th Aerospace Sciences Meeting and ExhibitAmerican Institute of Aeronautics and Astronautics
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Outline
• Motivation
• Flow Control
• Adaptive Airfoils
• Adaptive Wing Model
• Experimental results
• Conclusions
• Further work
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Motivation
• μAVs
Re = 104 - 105
• UAVs
Re = 105 - 106
• High Altitude
• Other
atmospheres (Mars)
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Airfoil Performance
• L/D reduced by more than an order of magnitude as Re
falls through 105
Figure from McMasters and Henderson
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Fluid Mechanics
LaboratoryUniversity 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
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Flow Control
• Any method which can modify the flow
• Can be passive or active
– Active flow control can respond to changes in conditions
– Requires energy input
• Active flow control is not a mature technology
• Shows promise
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Fluid Mechanics
LaboratoryUniversity 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)
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Fluid Mechanics
LaboratoryUniversity 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
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Some Adaptive Wing Research
• DARPA smart wing
– torsion control of entire wing using internal actuators
• DDLE wing
– rapid change in leading edge radius using mechanical actuator
• micro Flaps - MITEs (Kroo et. al.)
– multiple miniature trailing edge flaps with fixed displacement
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Fluid Mechanics
LaboratoryUniversity 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
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Previous Work
• Pinkerton and MosesA Feasibility Study To Control Airfoil Shape Using THUNDER, NASA TM 4767
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Fluid Mechanics
LaboratoryUniversity 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
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Adaptive Wing Construction
• Airfoil Profiles
– predicted prior to construction using given actuator placement
and full range of actuator motion
– actuator displacement increases maximum thickness and moves
point of maximum thickness aft
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Wing Construction
Base 4415
With Cutout
With mount-block
With Actuator
With spars
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Adaptive Wing Module
• A Single Module
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Testing Overview• Static model force measurements
– L/D enhancement using fixed actuator locations
• Static model PIV
– separation control using fixed actuator locations
• Dynamic model force measurements
– L/D enhancement using oscillating actuator motion
• Dynamic model Flow Visualization
– flow control using oscillating actuator motion
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Static Model Force Measurements
Corrected for Blockage as per Barlow, Rae and Pope, 1999
• Wind tunnel tests
– L/D declines as actuator displacement decreases then increases as
maximum displacement is reached at high AoA
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Static Model PIV
Separation
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Dynamic Model
• Oscillating upper surface– scanning LDS at 1 inch/sec with 1 Hz oscillation
Plot of displacement -vs- time as a distance transducer scans the model. Oscillations can be seen.
Units are mV -vs- seconds.
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Dynamic Model Force Measurements
• So far we have only tested at a Re of 25,000
• At this Re the forces are quite light
• They are lost in the noise
• We expect to have force measurements for higher Re
• Present model has protrusions on lower surface where the
skin attaches
• Next generation model will have the attachment hardware
recessed
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Fluid Mechanics
LaboratoryUniversity 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
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Dynamic Model Flow Visualizationα = 0˚
Actuator Fixed
Actuation 15 Hz
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Dynamic Model Flow Visualizationα = 9˚
Actuator Fixed
Actuation 45 Hz
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Conclusions
• Large static displacement of the actuator shows some
improvement in L/D
• Oscillation of the actuator has a pronounced effect on the
size of the separated flow
• The response to this oscillation does show a “sweet spot”
where separation is reduced maximally
– 15 Hz for 0˚
– 20 to 60 Hz for 9˚ with a maximum at 45 Hz
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Fluid Mechanics
LaboratoryUniversity 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
• Examine behavior with artificial turbulation
• Compare gains in performance with power required
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Fluid Mechanics
LaboratoryUniversity of Kentucky
Questions?