Thesis: Justine Schluntz

Computational fluid dynamics (CFD) is used in this thesis to model wind and tidal stream turbines and to investigate tidal turbine fence performance. There are two primary objectives of this work. The first is to develop and validate an actuator line method for the simulation of wind and tidal turbines which applies the blade forces to the flow field without the need for a regularisation kernel. The second is to study tidal fences using, in part, the newly developed actuator line method.

A potential flow equivalence method for determining the relative velocity and flow angle at the rotor blades in the actuator line method is proposed and validated in this thesis. Results for simulations using this method compare favourably with those from both experiments and alternative computational methods, although the present model’s results deviate from experimental results in the vicinity of the blade tips.

A CFD-embedded blade element-momentum tool is used to design rotors for operation in infinitely long tidal fences spanning a tidal channel. Rotors are designed for fences with several different blockage ratios, with those designed for high blockage flows having greater solidity than those designed for operation in fences with lower blockage. It is found that designing rotors for operational blockage conditions can significantly improve the power output achieved by a tidal fence.

Actuator line simulations of short (up to 8 turbines) fences with varying intra-rotor spacing and number of rotors confirm that hydrodynamic performance of the rotors improves as the spacing is reduced and as rotors are added to a fence. The position of a rotor within the fence impacts its performance; rotors at the ends of a fence extract reduced power compared to those at the centre of the fence, particularly for high tip speed ratios