Influence of ground roughness on the wake of a yawed wind turbine - a comparison of wind-tunnel measurements and model predictions

Wind-tunnel measurements in the wake of a three bladed horizontal axis wind turbine model (HAWT) operating in yawed conditions are presented. Measurements are made at a constant tip speed ratio within two neutrally-stratified turbulent boundary layers of different aerodynamic roughness length to investigate its influence on the wake trajectory. It is found that the wake is less deflected with increasing terrain roughness. The recorded flow field is then used to assess the predictive capability of two analytical wake models.