Scale model testing of tidal stream turbines: wake characterisation in realistic flow conditions

Tedds, Sian (2014) Scale model testing of tidal stream turbines: wake characterisation in realistic flow conditions. PhD thesis, University of Liverpool.

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Abstract

In this thesis the effect of uniform and profiled (non-uniform) steady flows on a scale-model tidal stream turbine (0.5m diameter) are experimentally investigated using the University of Liverpool high-speed recirculating water-channel. The power and thrust coefficients of the turbine with numbers of blades between two and six and various blade-pitch-angles are measured in uniform flow with low levels of turbulence at velocities ranging from 0.45m/s to 1.34m/s. With a three-bladed turbine at optimum blade-pitch-angle the power and thrust coefficients are compared in three different flow conditions of uniform flow with low turbulence intensity (2%), uniform flow with high turbulence intensity (5%) and non-uniform flow with high turbulence intensity (5%). Using an Acoustic Doppler Velocimeter (ADV) measurements of three-dimensional velocities are taken, initially, around the three-bladed turbine with optimum blade-pitch-angle. The velocities at five different heights and up to 7D downstream are probed where the upstream velocity is uniform with low turbulence levels and mean upstream velocity of 0.9m/s. Further ADV measurements are taken downstream of the three-bladed turbine through a horizontal centre-plane at lower velocities of 0.45m/s and 0.68m/s to probe the effect of Reynolds number on the turbine's wake. In addition wake measurements are taken downstream of the two-bladed turbine with optimum and non-optimum blade-pitch-angles to study the effect of differing tip-speed-ratios, thrust and power coefficients. Also the wake of the turbine support structure without blades is investigated. In a flow with high turbulence and mean velocity of 0.9m/s the wake of the three-bladed turbine is studied through a centre-plane equal to the turbine hub height. Further in a profiled flow, representative of a 1/5th velocity power law and upstream integral average velocity of 0.82m/s (over the turbine's swept area), characterisation of the flow downstream of the three-bladed turbine with optimum blade-pitch-angle is taken at five depths up to 5D downstream. These velocities are then compared in detail to those in uniform flow. Finally the ADV technique is used extensively throughout this thesis and, indeed, in most studies concerned with tidal turbine wakes. As issues regarding certain aspects of the ADV came to light during this study, the robustness of this technique is investigated by using two different ADV probe orientations and a comparison to 1D Laser Doppler Velocimetry is made.

Item Type:	Thesis (PhD)
Additional Information:	Date: 2014-02 (completed)
Subjects:	?? TA ??
Divisions:	Faculty of Science and Engineering > School of Engineering
Depositing User:	Symplectic Admin
Date Deposited:	08 Aug 2014 09:07
Last Modified:	16 Dec 2022 04:42
DOI:	10.17638/00018673
Supervisors:	Poole, Rob
URI:	https://livrepository.liverpool.ac.uk/id/eprint/18673