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Title: Turbulence modelling in the near-field of an axial flow tidal turbine in Code_Saturne
Author: Mcnaughton, James
ISNI:       0000 0004 2740 8970
Awarding Body: University of Manchester
Current Institution: University of Manchester
Date of Award: 2013
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This Thesis presents simulation of flow past laboratory-scale and full-scale tidal stream turbines (TST) using EDF's open-source CFD solver Code_Saturne. The work shows that detailed results may be obtained with confidence and that greater information on the loading and wake structure is available than other methods, such as blade element momentum theory.Results are obtained using a new sliding-mesh method that has been implemented in Code_Saturne as part of this work. The sliding-mesh method uses internal Dirichlet boundary conditions with values on the interface prescribed via a halo-point method. Parallel performance is optimised by a carefully-chosen method of exchanging information between specific processes. Validation is provided for flow past a rotating cylinder and a sphere.For the laboratory-scale TST, Reynolds-Averaged Navier-Stokes models are used to model turbulence. The k-omega-SST and Launder-Reece-Rodi (LRR) models yield good agreement with experimental values of power and thrust coefficients as a function of tip-speed ratio (TSR). The standard k-epsilon model is shown to perform poorly due to an overprediction of turbulent kinetic energy upstream of the rotor plane. The k-omega-SST model is then used to examine wake behaviour for parametric studies of turbulence intensity and TSR. Increased turbulence levels are shown to reduce the downstream propagation of the wake because of increased mixing. The near wake is influenced by the TSR, whilst the far wake is independent of TSR.The predicted effect of tidal conditions typical of the EMEC test site are considered for flow past Tidal Generation Limited's 1MW TST. The effect of sheared-velocity profiles leads to an increase in loading on an individual turbine blade at the point of a rotation where velocity shear is greatest. The effect of increased yaw angle leads to large fluctuations of the power coefficient, but smaller fluctuations of the thrust coefficient. Mean values of thrust and power decrease as a function of the cosine of the yaw angle and yaw angle squared respectively.
Supervisor: Apsley, David Sponsor: EDF Energy
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Tidal energy ; Tidal stream turbine ; Computational Fluid Dynamics ; Reynolds Averaged Navier Stokes ; Renewable Energy ; Turbulence modelling