The impact of wind direction yaw angle on cliff flows

The behavior of flow close to a cliff at heights relevant to wind turbines is explored using observations and simulations from a field experiment conducted at the Wind Energy Institute of Canada Prince Edward Island field site. There are 4 wind turbines located approximately 100 m from a 12 m high cliff and a fifth turbine located 500 m inland. During the field experiment, ongoing mast‐based observations were supplemented with additional sonic anemometers and Doppler lidars. Consistent with wind tunnel measurements and previous model simulations, a small speedup in the flow (~3‐5%) at the turbine hub‐height (of 80 m) is observed when the flow is perpendicular to the cliff. The objective here is to determine the degree to which the magnitude of the speedup, or horizontal distance over which it is manifest, changes as the flow deviates from the perpendicular impingement angle (ie, for nonzero yaw angles). Results indicate that the zone of deceleration upwind of the cliff and the downwind acceleration zone are maintained with flow ±25° to the perpendicular. Further, there is little change in the relative magnitude of either the wind speed or the turbulence intensity with modest deviations from perpendicular flow. However, as the angle from the perpendicular increases (ie, flow becomes increasingly parallel to the coast), the impact on wind speed and turbulence intensity decreases and is manifest over narrow and spatially less coherent regions.