Influence of wind direction on flow over a cliff and its interaction with a wind turbine wake

Abstract

This work investigates the effect of wind direction on the flow over a cliff and its interaction with the wake of a wind turbine sited on the cliff. The cliff is modeled as a forward-facing step, and five wind directions are tested (θ=0°, 15°, 30°, 45°, and -45°), where 0° represents a wind direction perpendicular to the cliff edge. The flow becomes increasingly three-dimensional with the increase in the wind direction magnitude and a cross-stream flow separation develops from the cliff leading edge. The turbulence kinetic energy decreases for wind directions higher than 15°, which is due to the absence of the streamwise flow separation for higher wind directions. The cross-stream flow development in the base flow affects the shape of the turbine wake. A two-dimensional Gaussian fit is performed on the wake velocity deficit, which shows a slight departure from self-similarity in the lateral direction. The wake recovery slows down for wind directions higher than 15°, which is consistent with the decrease in the wake growth rate for θ>15°. The wake shows higher deflection and tilt angle for higher wind directions. Analysis of the streamwise momentum in the wake reveals that the advection terms play a role in slowing the wake recovery for higher wind directions.