The effect of freestream turbulence on fixed and flapping micro air vehicle wings

Fisher, A 2013, The effect of freestream turbulence on fixed and flapping micro air vehicle wings, Doctor of Philosophy (PhD), Aerospace, Mechanical and Manufacturing Engineering, RMIT University.


Document type: Thesis
Collection: Theses

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Title The effect of freestream turbulence on fixed and flapping micro air vehicle wings
Author(s) Fisher, A
Year 2013
Abstract This thesis details an experimental investigation into the effects of elevated levels of large-scale freestream turbulence on the aerodynamics of a micro air vehicle wing in fixed, flapping, and pitching configurations. Such large-scale turbulence is typical of the low altitude MAV flight environment, but is often overlooked. Time-resolved pressure distributions over the wing were obtained and smoke wire flow visualization was used in an attempt to relate these pressures to the major flow structures. Elevated levels of turbulence were found to enhance the time-averaged performance of the fixed wing, but only via relatively infrequent, but strong peaks in upper surface suction of short duration, caused by the formation of leading edge vortices (LEVs). Therefore it was concluded that this enhancement in time-averaged performance would unlikely be useful for MAVs.

On the flapping wing, at low flapping frequencies, elevated turbulence tended to narrow the hysteresis loop in the lift curve caused by flow separation. At higher flapping frequencies the net effect of turbulence on lift was not as significant, although elevated turbulence was found to “smear out” the phase-averaged suction peak caused by the LEV produced during the initial part of the stroke. Flow visualization suggested that this was due to the large scales of oncoming turbulence modulating the size and timing of the LEV. On the wing undergoing pure pitching motion, the effects of pitch rate and angle of attack could be decoupled, and results suggested that freestream turbulence has little effect on pitch-rate induced hysteresis, whereas it has a significant effect on hysteresis induced by flow separation, as was found on the flapping wing.
Degree Doctor of Philosophy (PhD)
Institution RMIT University
School, Department or Centre Aerospace, Mechanical and Manufacturing Engineering
Keyword(s) micro air vehicle
MAV
flapping
aerodynamics
pressure measurement
atmospheric turbulence
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Created: Fri, 01 Nov 2013, 07:45:01 EST by Denise Paciocco
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