Cardiff University

Simulation and measurement of tidal stream turbine wakes: here results from ANSYS Fluent have been combined with flume tank testing at IFREMER in Boulogne-Sur-Mer, France.

Problem:

Understanding the nature of wakes from tidal stream turbines is crucial if they are to fulfil their potential and make a significant contribution to reliable renewable energy. Being able to accurately characterize a turbine wake is necessary in order to calculate mechanical loading, array layout and potential environmental impacts of the deployment of multiple turbines. This image combines a computational simulation of a wake, calculated using an advanced turbulence model, with a long exposure photograph taken at the IFREMER flume testing facility. Data from this test has been used to validate wake simulations using this particular type of turbulence model, which promises to produce more accurate predictions of both the nature and extent of the wake behind a tidal stream turbine. This enables better prediction of the fluctuating loads experienced by downstream turbines within an array, increasing reliability and reducing the costs of tidal energy.

Solution:

ANSYS Fluent has advanced turbulence models, such as the detached-eddy simulation (DES) model, which combine the computational economy of a two-equation RANS model with the resolution of large-eddy simulation (LES) where it is required in the wake region. Simulations were conducted to improve the prediction of the turbine wake while using full turbine geometry. Previously, researchers who wished to model wakes with LES have had to simplify the turbine geometry via the use of actuator lines or porous discs, in lieu of full turbine geometry. The image submitted combines a DES simulation of a turbine with a photograph of flume tank validation testing. ANSYS CFD predicts both the length and character of the wake; detailed simulations indicate areas to concentrate on during the time-limited flume test.

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