Towards a better understanding of yawed turbine wake for efficient wake steering in tidal arrays

Tidal stream turbines (TST) deployed in open-water energetic sites are often unintentionally at yaw to the incoming flow that causes performance degradation and deflection of the wake. Wake steering is a popular concept in wind arrays where the upstream turbine is operated intentionally at yaw to steer the wake away from a downstream turbine. To explore such arrangements for TST arrays, a synergistic experimental and numerical campaign was undertaken to characterize a TST performance and wake deflection subjected to +/- 15 degrees yawed inflow. The near-wake characterization study was performed using complementary acoustic Doppler velocimetry measurements and 3D computational fluid dynamics. The experiments show a similar to 10% reduction in the maximum power coefficient. In the near field, the deflected wake morphed into an elliptical shape due to the formation of two counter-rotating vortices. The wake deflection results in enhanced momentum transfer and dissipation, leading to accelerated energy recovery. When the upstream turbine is yawed, available kinetic energy in the flow for the downstream turbine is at least 50% higher with the turbine array in a staggered configuration compared to the inline configuration. Our results provide guidance in reducing the cross-stream and downstream spacing between turbine units in an array. (C) 2021 Elsevier Ltd. All rights reserved.