CFD simulations of a full-scale tidal turbine: comparison of LES and RANS with field data

CFD simulations have been performed for a geometry-resolved full-scale tidal-stream turbine and compared with experimental data from the EMEC test site in the Orkney Isles. The mesh comprises two regions: a rotating part, containing the turbine, and a stationary outer part, including the support tower. A sliding-mesh interface couples the two parts.Initially, Reynolds-averaged Navier-Stokes and large-eddy simulations were performed using an inflow velocity profile representative of the test site but low inflow turbulence, yielding satisfactory mean power coefficients. LES with synthetic turbulence prescribed at inlet was then employed to try to predict realistic load fluctuations. Load fluctuations (power, thrust and blade bending moments) may arise from onset mean velocity shear, influence of the support tower, blade-generated turbulence, approach-flow turbulence and waves. Inflow statistics were prescribed to match the vertical distribution of mean velocity, Reynolds stresses and length scales determined from a channel-flow simulation, with additional factoring of stresses and length scales to match as far as possible those measured on-site. LES simulations with synthetic turbulence at inflow satisfactorily reproduces the spectral distribution of blade bending moments provided that spectra are normalised by variance to reflect the relatively small number of rotations computed.