Experimental and Numerical Investigation on the Mechanism of Sediment Scouring Around a Horizontal-Axis Tidal Stream Turbine

Understanding detailed flow characteristics around a horizontal-axis tidal stream turbine is important in designing the turbine and assessing environmental impacts. Building upon recent research by Supervisor 2 on 3D numerical modelling of seabed scouring around a pile-supported horizontal axis tidal turbine under steady current condition (Zhang et al. 2015 JMST, 23, 929-936), we aim to study detailed flow structure and bed scouring around a tidal turbine subject to oscillatory flows using a 3Dnumerical model and its experimental validation.

Two important characteristics of tidal current is (i) that it is essentially oscillatory, but (ii) that individual flow profile is very different for each location. Supervisor 1 has developed an experimental facility (a U-tube with pistons on both ends) that can generate oscillatory flow of arbitrary profile over very wide ranges of parameters such as stroke length (up to 1 m) and frequency of the piston (up to 1 Hz). We will use sediment bed of various types (namely, sand, silt and combinations) and install a scaled model of tidal stream turbine in the U-tube. For each experimental case, the flow field around the turbine will be measured using a particle image velocimetry at as many 2D planes as desired. Scouring pattern will also be monitored using a high-speed video camera.

The experimental data will be used to validate the 3D numerical model. Then the model will be used to carry out further parametric studies of scouring around an array of tidal turbines. The research outcome is expected to provide useful guideline for scouring protection for the horizontal-axis tidal stream turbine.

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