Validation of hydrokinetic turbulent wake predictions and analysis of wake recovery mechanism

Turbulent simulations are performed for a three-bladed, horizontal-axis hydrokinetic turbine for two different tip-speed-ratios using a resolved rotating blade model with a sliding interface. The thrust, power and intermediate wake predictions are validated by comparison with experimental data, and the results are analyzed to understand the wake recovery mechanism. The thrust and power predictions compare within 4.3% of the experimental data for both tip-speed ratios. The wake predictions improve with grid resolution, and MILES, which includes resolved anisotropic turbulence, performs better than both URANS and IDDES models. Nonetheless, the errors in the intermediate wake predictions are large ~27%.These errors are due to under prediction of cross-plane turbulent fluctuations, which delays the shear layer growth and wake recovery, and are caused by numerical dissipation of resolved turbulence at the interface between the rotating and stationary domains. The far-wake deficit shows self-similarity with a Gaussian profile, and wake recovery is independent of the tip-speed ratio. Future work should focus on investigating improved interface boundary conditions, and procuring additional experimental data for validation