Dynamic Stall Control Using Synthetic Jets

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Embargoed until 2016-10-30
Copyright: Yen, Joshua
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Abstract
Dynamic stall is an unsteady flow phenomenon that occurs on helicopter and wind turbine rotor blades when rapidly pitched beyond their corresponding static stall angle. It is characterised by formation of large vortices that initially increase lift but then induce strong and potentially damaging pitching moments when the vortices shed into the wake, and cause severe vibrations and cyclic loading. Consequently, the performance of helicopters and wind turbines are significantly limited by the onset of dynamic stall and manifestation of its concomitant vortex. Synthetic jets have shown great potential to control dynamic stall by maintaining the enhanced lift while decreasing drag and pitching moment excursions. However, the control mechanism is poorly understood and remains unclear. This dissertation investigates and develops a better understanding of dynamic stall control using synthetic jets through both physical experiments and numerical simulations of airfoils sinusoidally oscillated through large angles of attack. The dynamic stall process and its alteration with synthetic jets are explored to identify possible control mechanisms, and are also examined in the context of vorticity creation and vertical axis wind turbines. Larger pressure gradient fluctuations was the mechanism identified for promoting the onset of dynamic stall with low frequency synthetic jet actuation compared to high frequency actuation. Synthetic jet actuation also altered the vorticity created on both a stationary flat plate and a sinusoidally oscillating airfoil through modification of the boundary vorticity flux. Additionally, actuation improved the flow around a vertical axis wind turbine blade and demonstrated substantial performance enhancements could be gained by vertical axis wind turbines at low blade-speed ratios. The findings help develop a better understanding of dynamic stall and its control using synthetic jets and will allow the performance of helicopters and wind turbines to be improved in the future.
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Author(s)
Yen, Joshua
Supervisor(s)
Ahmed, Noor
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Publication Year
2016
Resource Type
Thesis
Degree Type
PhD Doctorate
UNSW Faculty
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