Aerodynamics of finite-span inclined flat plates in ground proximity
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Photovoltaic power generation has grown to become a multi-billion dollar global sector, aiding in the switch to renewable energy sources to limit the progress of climate change. However, relatively high energy production costs at the utility scale currently limits capacity expansion. A comprehensive understanding of salient flow physics and the relation to associated aerodynamic loading are critical in reducing costs through appropriate sizing of support structures, improving site selection criteria, and providing guidance for future load reducing flow control strategies. The research presented in this thesis is centred around this effort, as flow development and aerodynamic loading on finite-span inclined flat plates in close ground proximity subject to both steady and unsteady flow conditions are experimentally investigated. The supporting data consists of direct force measurements, surface flow visualization, and particle image velocimetry. In the first part of the thesis, the influence of aspect ratio, pitch angle, and ground proximity under steady headwind and tailwind conditions on the aerodynamic forcing and flow over inclined flat plates was investigated. Ground proximity-related effects are most notable when the plate was closer than 0.75 chord lengths from the ground, near the stall angle, where pronounced changes in the midspan and wake flow development take place. The modulation of free flight aerodynamics by ground proximity is dependent on the specific combination of aspect ratio, angle of attack, and wind direction. Notably, for headwinds, the increase in static pressure on the underside leads to increased aerodynamic loads, while for tailwinds, either a decrease or insensitivity in aerodynamic loads is observed with closer ground proximity depending on the aspect ratio. In the second part of the thesis, the yaw angle of a square plate at an angle of attack of 30° was varied between 0° and 180° to simulate steady wind directions. Ground effect-related aerodynamic changes are strongly dependent on yaw angle. Between yaw angles of 0° and 90°, a ground height invariant suction side flow is observed; however, the aerodynamic loading increases due to a higher static pressure on the ground facing area relative to free flight conditions. For yaw angles between 90° and 120°, the suction side and thus the loading is ground height invariant. Between yaw angles of 120° and 150°, notable sting effects confound any ground proximity related effects. Further increase in yaw angle, up to 180°, leads to an onset of stall with decreasing ground proximity reducing the aerodynamic loading. For the third part of the thesis, the aerodynamics of a square inclined plate under moderate ground effect is investigated for yaw angles between 0° and 30°. Transient changes in wind direction was modelled by a yaw rotation from 0° and 30° as well as from 30° and 0°, over 3.8 convective time units. Peak transient lift coefficients are above 10% of steady state levels immediately following the yaw rotation. Both the tip vortex circulations and the lift coefficient exhibit a consistent hysteresis, highlighting the important role tip vortices play in lift generation under dynamic conditions.
Cite this version of the work
Supun Pieris (2023). Aerodynamics of finite-span inclined flat plates in ground proximity. UWSpace. http://hdl.handle.net/10012/19853