Fluid Mechanics Laboratory University of Kentucky Active Control of Separation on a Wing with...

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

Fluid Mechanics


Outline

• Motivation

• Flow Control

• Adaptive Airfoils

• Adaptive Wing Model

• Experimental results

• Conclusions

• Further work

Fluid Mechanics


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

Fluid Mechanics


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


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

Fluid Mechanics


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


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


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

Fluid Mechanics


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

Fluid Mechanics


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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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.

Fluid Mechanics


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

Fluid Mechanics


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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Dynamic Model Flow Visualizationα = 0˚

Actuator Fixed

Actuation 15 Hz

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Dynamic Model Flow Visualizationα = 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

Fluid Mechanics


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

Fluid Mechanics


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