Three-Dimensional Unsteady Hydrodynamics of Tidal Turbines
type: CreativeWork
description: Tidal power is an emerging industry in the renewable energy sector; a development which is uniquely beneficial to the United Kingdom, which has a significant tidal resource and a mature knowledge base for turbine technology. One of the challenges facing the tidal industry is the harsh nature of the operating environment, due to the presence of waves and ocean turbulence. The turbines sustain damage due to the fluctuating loads that result from the unsteady flow, either from high-cycle fatigue or from extreme loading events exceeding the ultimate tensile strength of components. In this thesis, the problem of unsteady loading is addressed by identifying the shortcomings of the models currently used to estimate unsteady forces on turbines due to gusts, and by providing new low-order modelling tools for more accurate calculations of these forces. The focus of this thesis is on the assumption of locally two-dimensional (2D) flow used in the majority of turbine loading models. Tidal turbines are strongly three-dimensional (3D) in shape, with low aspect ratio and strongly tapered blades. As such, the assumption of locally 2D flow is unlikely to apply. In this thesis the consequences of this assumption are explored, dividing 3D effects into two categories: 3D geometry effects, and the effects of 3D features in the incoming unsteady flow. The effect of these 3D features is shown by studying generic aerofoil geometries and a model tidal turbine, using a combination of first-order inviscid modelling with a vortex lattice model (VLM) and higher-order viscous modelling with URANS CFD. The VLM is used in the frequency-domain to perform a parametric study of a range of aerofoil geometries. The unsteady response of aerofoils with finite span, rotation or varying planform is shown to deviate strongly from 2D predictions by linear analytic theory (such as the Theodorsen or Sears functions). At low reduced frequencies and low aspect ratios, 3D effects are strongly visible. In the vici…
abstract: Tidal power is an emerging industry in the renewable energy sector; a development which is uniquely beneficial to the United Kingdom, which has a significant tidal resource and a mature knowledge base for turbine technology. One of the challenges facing the tidal industry is the harsh nature of the operating environment, due to the presence of waves and ocean turbulence. The turbines sustain damage due to the fluctuating loads that result from the unsteady flow, either from high-cycle fatigue or from extreme loading events exceeding the ultimate tensile strength of components. In this thesis, the problem of unsteady loading is addressed by identifying the shortcomings of the models currently used to estimate unsteady forces on turbines due to gusts, and by providing new low-order modelling tools for more accurate calculations of these forces. The focus of this thesis is on the assumption of locally two-dimensional (2D) flow used in the majority of turbine loading models. Tidal turbines are strongly three-dimensional (3D) in shape, with low aspect ratio and strongly tapered blades. As such, the assumption of locally 2D flow is unlikely to apply. In this thesis the consequences of this assumption are explored, dividing 3D effects into two categories: 3D geometry effects, and the effects of 3D features in the incoming unsteady flow. The effect of these 3D features is shown by studying generic aerofoil geometries and a model tidal turbine, using a combination of first-order inviscid modelling with a vortex lattice model (VLM) and higher-order viscous modelling with URANS CFD. The VLM is used in the frequency-domain to perform a parametric study of a range of aerofoil geometries. The unsteady response of aerofoils with finite span, rotation or varying planform is shown to deviate strongly from 2D predictions by linear analytic theory (such as the Theodorsen or Sears functions). At low reduced frequencies and low aspect ratios, 3D effects are strongly visible. In the vici…
author: Smyth, Amanda Sofie Magdalena
language: en
keywords: unsteady flow, tidal, tidal energy, tidal power, tidal stream, horizontal axis, turbulence, 3D, strip-theory, unsteady aerodynamics, incompressible, unsteady fluid dynamics, 3D effects, 3D geometry, wake modelling, CFD, vortex lattice, URANS, Theodorsen, Sears, Loewy, inviscid, unsteady hydrodynamics, eigenmodes, modal decomposition, unsteady load
license: https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/cbee5c29-755c-4625-bf03-7106d96f5627/download
license: https://www.rioxx.net/licenses/all-rights-reserved/
date published: 2020-03-02
date modified: 2026-07-22T22:24:17Z
provider: Cambridge University
publisher: Networked Digital Library of Theses and Dissertations
type: WebPage
source organization: University of Cambridge

PropertyValue
property ID: DOI
value: 10.17863/CAM.48853