Influence of operating conditions on wake recovery of a yawed tidal stream turbine

Yawed inflow results in performance degradation and downstream wake deflection of a tidal stream turbine (TST).  Previous studies have explored performance degradation and wake recovery for yawed TSTs operating at rated rotational speed (λ_rated).  However, array operators often need to operate the turbines at speeds slower than λ_rated to reduce fatigue load on blades and increase the operational life of the turbine. Momentum and energy recovery mechanisms under those off-design conditions are not well known. We will discuss detailed near-wake laboratory measurements for a 30° yawed turbine at three different operating conditions (λ_rated, 0.5λ_rated, and 0.1λ_rated). Increasing λ was observed to directly influence the wake deflection magnitude for yawed inflow, increasing the cross-stream advection, which is the largest contributor to momentum recovery. We will discuss various insights from our study using an acoustic Doppler velocimeter on the dependence of turbine rotational speed on wake recovery for yawed inflows.