Time resolved particle image velocimetry experimental study of the near wake characteristics of a horizontal axis wind turbine

Wind tunnel experiments at a model scale have been carried out to investigate the flow characteristics in the near wake of a wind turbine. Time resolved particle image velocimetry (TRPIV) measurements are applied to visualize the wind turbine wake flow. The instantaneous vorticity, average velocities, turbulence kinetic energy, and Reynolds stresses in the near wake have been measured when the wind turbine is operated at tip speed ratios (TSRs) in the range of 3-5. It was found that wind turbine near the wake flow field can be divided into a velocity increased region, a velocity unchanged region, and a velocity deficit region in the radial direction, and the axial average velocities at different TSRs in the wake reach inflow velocity almost at the same radial location. The rotor wake turbulent kinetic energy appears in two peaks at approximately 0.3R and 0.9R regions in the radial direction. The Reynolds shear stress is less than the Reynolds normal stresses, the axial Reynolds normal stress is larger than the Reynolds shear stress and radial Reynolds normal stress in the blade root region, while the radial Reynolds normal stress is larger than the Reynolds shear stress and axial Reynolds normal stress in the blade tip region. The experimental data may also serve as a benchmark for validation of relevant computational fluid dynamics (CFD) models.