Fluid Mechanics Laboratory

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Active Control of Separation on a Wing with
Conformal Camber
The 39th Aerospace Sciences Meeting and
Exhibit American Institute of Aeronautics and
Astronautics

• David Munday and Jamey Jacob
• Department of Mechanical Engineering
• University of Kentucky
• 8 January 2001

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Outline

• Motivation
• Flow Control
• Adaptive Airfoils
• Adaptive Wing Model
• Experimental results
• Conclusions
• Further work

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Motivation

• µAVs
• Re 104 - 105
• UAVs
• Re 105 - 106
• High Altitude
• Other
• atmospheres (Mars)

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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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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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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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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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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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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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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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Previous Work

• Pinkerton and MosesA Feasibility Study To
  Control Airfoil Shape Using THUNDER, NASA TM 4767

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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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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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Wing Construction
Base 4415
With Cutout
With mount-block
With Actuator
With spars
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Adaptive Wing Module

• A Single Module

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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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Static Model Force Measurements

• Wind tunnel tests
• L/D declines as actuator displacement decreases
  then increases as maximum displacement is reached
  at high AoA

Corrected for Blockage as per Barlow, Rae and
Pope, 1999
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Static Model PIV
Separation
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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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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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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 lt 50

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Dynamic Model Flow Visualization
a 0
Actuator Fixed
Actuation 15 Hz
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Dynamic Model Flow Visualization
a 9
Actuator Fixed
Actuation 45 Hz
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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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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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Questions?