The Performance Assessment of Wave and Tidal Array Systems (PerAWaT) project, launched in October 2009 with £8m of ETI investment. The project delivered validated, commercial software tools capable of significantly reducing the levels of uncertainty associated with predicting the energy yield of major wave and tidal stream energy arrays. It also produced information that will help reduce commercial risk of future large scale wave and tidal array developments.
This document outlines the issues associated with modelling the far wake region within an array of tidal turbines. A review of the existing literature is presented which provides an overview of both the applicable modelling options which characterise the wake region of interest. The GH far wake model is described and the modelling approach justified. The GH far wake model simplifies the fundamental Navier-Stokes equations to allow a computationally efficient method to evaluate far wake development. To account for any surrounding bounding effects a hybrid method is used. The model is initialised by the GH device scale models and then the solution propagates downstream. The key parameters which affect the model include: the ambient flow turbulence and the potential impact of bounding surfaces and/or other surrounding turbines. Wake merging models are used to combine multiple wakes. Flow diagrams of the GH far wake model algorithms are presented. Existing validation of the aspects of the modelling method are presented.
The theory and methodology of the GH far wake model have been detailed and an account of how the model will be incorporated in the TidalFarmer beta code is provided. The GH far wake model is an arrangement of several models which collectively provide an array far wake modelling method. The eddy-viscosity model is the core flow solver which predicts the recovery of a single wake based on the initial velocity deficit profile and the ambient flow turbulence intensity. A split modelling approach decouples the vertical and lateral boundary conditions allowing a fast computation of several 3-d wakes. By combining the split models a representative wake is evaluated. The model utilises an elliptical Gaussian profile to account for the interaction with the bounding free-surface and seabed.