|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 report describes the formulation of and results obtained from an actuator disk model of a tidal turbine. The presented work falls into the first category of farm scaled models, namely blade modelled/turbine resolved three dimensional Reynolds averaged Navier-Stokes (RANS) simulations. Output from these models will be used for the development of shallow water equation models of turbines which are to be incorporated into basin scale models in WG2 WP3. The advantages of using a model of this type in a RANS simulation is that the time to solution is much faster than for blade-resolved models allowing small arrays of turbines to be modelled.
In addition to describing the formulation of the model it has been applied to the simulation of three test cases. The first case is for a single three bladed horizontal axis tidal turbine in a flume. This test case is based on the experiments performed in the EDF flume in Chattou which have previously been modelled by the University of Oxford. Comparisons to the predicted thrust and power coe cient distributions as functions of tip-speed ratio are made with these results and with the results from the EDF experiments. The coeffi cients used for the actuator disk model are drawn from information derived from blade resolved simulations performed in Edinburgh (in WP5) and from lift/drag data from Garad-Hassan’s “Tidal-Bladed” programme.
The second and third cases model experiments performed on arrays of turbines by Manchester University. In these simulations the centre rows of a very wide array are modelled and the two cases considered represent rotors in series (i.e. directly downstream of each other) and in a staggered grid. Comparisons of predicted thrust and power coeffi cient distributions as functions of tip-speed ratio are made against data from the Manchester tests.
Finally, a depth averaging analysis has been performed on the results obtained from the simulations. By presenting the velocity and turbulence information in this way, models of turbine for shallow water simulations can be checked and calibrated, providing, for the first time, detailed information for this purpose. The depthaveraging analysis of the three dimensional RANS results is only possible because of recent advances in flow visualisation tools which allow statistical information, including mean values, to be derived from fully three dimensional data.
The work presented in D5a concentrates on steady-state cases where the mean upstream turbulent flow onto the turbine (or array) is of constant and uniform velocity. The subsequent deliverable D5b will examine unsteady flow