Purvis, Richard; (2002) Rotor blades and ground effect. Doctoral thesis (Ph.D), UCL (University College London).

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Abstract

This thesis uses numerical, asymptotic and flow structural techniques to examine various aspects of rotor blade flows and ground effect. It explores two-and three-dimensional flows, generally concentrating upon regimes that have a degree of relevance to typical rotor blade flows. Chapter 2 considers, as a first step towards understanding a general rotor blade system in ground effect, a finite rotating disc near horizontal ground. More specifically, it concentrates on determining the layer shape beyond the disc rim that, due to the presence of the ground, cannot remain flat without violating a pressure condition across it. Chapter 3 examines the flow past many blades in ground effect using both a numerical approach and considering various limits of interest to illuminate some of the important features such as enhanced lift and sheltering effects. Chapter 4 then extends this by exploring the many blade limit, whereby the flow develops a periodic structure once sufficiently many blades have been passed. We then move on to three-dimensional configurations. Chapter 5 takes the previous work further by considering the interactive case that arises after a very large number of blades have been passed, generating a pressure-displacement interaction in the boundary layer. We examine the case of three-dimensional blades, considering the full triple deck problem and then the short blade limit, investigating the flow structure for this physically relevant case. Chapter 6 considers the flow past a three-dimensional hump on a blade of a rotor, examining the flow structure and solution and tentatively using this to propose a description of the flow past the trailing corner of a typical rotor blade. Finally Chapter 7 returns to ground effect, exploring the flow past a single, three-dimensional blade near the ground. It uses a compact difference technique to examine the flow solution for a particular blade shape and investigates the idea of change-over points, where the effective leading edge becomes a trailing edge switching the boundary conditions, these points being generally unknown in advance.

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