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Title: Low aspect-ratio rigid, flexible and membrane wings at low Reynolds numbers
Author: Tregidgo, Luke
Awarding Body: University of Bath
Current Institution: University of Bath
Date of Award: 2013
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The interest in developing small, payload-carrying Micro Air Vehicles (MAVs) with a maximum linear dimension of six inches or below is as strong as ever, with both military and civilian bodies interested in the remote sensing capabilities such a vehicle would provide. However significant challenges remain in developing such aircraft and the research presented here addresses specific issues in the field of fluid-structure interactions for flexible wings. Wind tunnel tests were conducted on rectangular, aspect-ratio-two, rigid and flexible wings (including membrane wings) in an open-jet, closed-loop facility at the University of Bath. The chord Reynolds number for the experiments was in the range 34,000≤Rec≤69,000. Measurements of force, deformation and flow velocities were taken using a variety of techniques including Digital Image Correlation (DIC) and Particle Image Velocimetry (PIV). The key findings were that flexible wings experience different eigenmode vibrations and amplitudes. This was shown to be dependent on the incidence angle of the wing to the incoming flow. Through measurements of the flow-field it was further shown that as the incidence angle increased, the behaviour of the separated shear-layer was responsible for the changes in structural mode. There was a further change as the flow became fully separated and dominated by bluff-body vortex shedding. Dynamic pitching of the wings, to simulate gust encounters, highlighted the complex nature of the fluid-structure interactions. Time lags between the flow features and structural response suggested hysteresis effects also play a role. Tests conducted on free-to-roll wings demonstrated that self-excited ‘wing rock’ oscillations are possible for this configuration of wing at incidence angles either side of stall. These oscillations were driven by dynamic differences in the strength and position of the two tip vortices. When subjected to forced pitching manoeuvres, synchronisation of the roll phase and frequency were observed. Given the right combination of pitch frequency and amplitude, this offered a method of attenuating the self-excited rolling motion.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available