Numerical Prediction of Cavitation for a Horizontal Axis Tidal Turbine

Abstract

This paper aims at assessing cavitation in a scaled tidal turbine geometry through numerical simulations. Cavitation occurrence is predicted by using the Singhal cavitation model, based on the Rayleigh-Plesset equation, for treating bubble dynamics. Turbulence is modelled adopting a Reynolds Averaged Navier Stokes (RANS) approach, specifically employing the Shear Stress Transport (SST) k-ω model to simulate the fluid flow. The Reboud density function is applied to adjust the eddy viscosity computation in the cavitation region. Initially, cavitation and turbulence models are validated using a NACA 66 (mod) hydrofoil profile as a test case. Numerical and experimental pressure coefficients are compared on the hydrofoil suction side for a selected cavitation condition. A Mesh Sensitivity Analysis (MSA) is performed to ensure simulation accuracy, comparing numerical results with experimental data on the Horizontal Axis Tidal Turbine (HATT) scaled domain. Based on this analysis, the optimal computational grid is selected. Experimental and numerical power and thrust coefficients are then compared across different tip speed ratios. Finally, cavitation occurrence is evaluated for four different regimes, namely the cut-in, the peak-power, the curve highest velocity and the off-set tip speed ratios. Computational Fluid Dynamics (CFD) solutions reveal vapor formation around turbine components, highlighting regions most exposed to cavitation onset.