Numerical Simulation of Cavitation on a Horizontal Axis Tidal Turbine

For tidal turbines mounted on floating structures the possibility ofcavitation occurring on the blades is higher than for seabed mountedtidal turbines. In this study we present Reynolds-Averaged Navier-Stokes (RANS) solutions of the well-studied Southampton three bladedhorizontal axis tidal turbine (HATT). The numerical simulations werecarried out using the ReFRESCO viscous flow solver using three typesof simulations: (i) steady wetted flow; (ii) unsteady wetted flow and(iii) unsteady cavitating flow. The wetted flow simulations gave overallgood prediction of thrust and power coefficients over the entireexperimental range of tip speed ratios (TSRs), with the unsteadysolution providing the better result. Low numerical uncertainties wereobtained for medium to high TSRs and larger for low TSR values,where the flow is transitional and highly separated. The dynamiccavitation simulation was carried out for the case of a cavitationnumber of 0.63 at a TSR of 7.5. The simulations showed a goodagreement of the extent of the sheet cavity. However, the dynamics ofthe sheet cavities have not been fully captured and the power and thrustcoefficients are under predicted compared to the experiments. This ismost likely due to lack of mesh resolution outside the wetted flowboundary layer where the cavity dynamics occur, and due to highnumerical and experimental uncertainties for such a complex flow case.The simulations showed that existing methodology used for computingcavitation on marine propellers could be applied to HATTs, yieldingreliable results. Importantly, simulation of cavitation on HATTs couldbe used as input for noise and erosion predictions