Synergizing Helix Active Wake Mixing with Dynamic Yawing: An Exploration Study using Porous Discs in a Wind Tunnel

Abstract Clustering multiple turbines in close vicinity gives rise to efficiency losses due to the energy extraction of upstream turbines, a phenomenon known as the wake effect. The risk wake-induced power losses pose for the economic feasibility of wind farm projects motivated several methodologies aimed at mitigating the wake effect by dynamically exciting one operational parameter of the upstream turbine. Among them are dynamic yawing, which sinusoidally varies the yaw angle of the turbine with the wind, and helix active wake control, which dynamically manipulates the turbine thrust. This study is the first to explore the potential of exciting two operational parameters simultaneously by synergizing dynamic yawing and helix active wake control. Therefore, we conduct wind tunnel experiments using a yawable porous disc model modified to mimic the effect of the helix on the flow. A particular focus is put on the relative orientation between helix and dynamic yawing. Results indicate that wake recovery enhancements achievable by synergizing helix and dynamic yawing are in the same range as both methods individually; however, at 50% lower excitation frequencies than only helix and 10° smaller yawing amplitudes compared to only dynamic yawing.