Horizontal Axis Wind Turbines under Yaw-Misalignment at High Reynolds Numbers – Experimental and Model Performance Predictions*

This study examines yaw and tip-speed ratio effects on horizontal axis wind turbine thrust, power, and wake development through comparisons of experimental measurements and model predictions. The experiments are conducted in the High Reynolds number Test Facility at Princeton University, where field-relevant Reynolds numbers (Re_D = 4 × 10⁶) and tip-speed ratios (3.5 ≤ λ ≤ 7.5) are achieved by scaling pressure in place of velocity. Yaw angles spanning -45° ≤ γ ≤ 45° are explored, and turbine performance is characterized through measurements of the generated thrust, power, and wake. As the yaw-misalignment is increased, the thrust and power decrease and the wake deflects laterally; effects which show a tip-speed ratio dependence. Leveraging recent analytical modelling improvements, these trends are compared to a Unified Momentum Model (UMM) for rotors at arbitrary inflow angles and thrust coefficients. The experimental and model-predicted power outputs show good agreement across all yaw angles when the turbine is operated at its design tip-speed ratio and when power is maximized through tip-speed ratio control. Agreement between the experimental and model results is less at off-design conditions, however the UMM predictions are improved over those from classical momentum theory and other empirical methods. These results help identify promising directions for future model development, towards the goal of developing a robust, yet simple model for use in real-time wind farm control.