Wind Turbine Wake Recovery for a Downwind Configuration

A downwind turbine configuration offers the opportunity for the use of lighter, larger, and more flexible blades by relaxing blade-tower clearance constraints.This design can reduce costs and increase farm power in flow-aligned rows while expanding rotor-swept area for floating turbines. However, the tower shadow effect raises concerns about periodic blade loading, increased bending moments, and reduced efficiency. This study examines 0.1 m-radius model turbines subjected to a 3 m/s freestream velocity in the Portland State University wind tunnel, directly comparing upwind and downwind orientations. Power output was measured using hub-mounted generators, and stereo particle image velocimetry (PIV) was used to characterize mean velocity fields and turbulent Reynolds stresses in the wake. Four adjoining 20 cm × 20 cm streamwise vertical planes were blended to create a detailed map of the wake structure from 0.5–2.5 rotor diameters (D) downstream. Two spanwise vertical planes were also used capturing the wake at 1D, 2D, and 3D downstream of the turbine. Results demonstrate that turbine geometry and orientation significantly affect wake development, turbulence distribution, and power efficiency, while the tower shadow effect has negligible impact on power. Comparing wake dynamics and power production between upwind and downwind turbines informs the feasibility, performance trade-offs, and potential advantages of adopting downwind configurations for utility-scale wind energy applications.