On the homogenization of turbulent flow structures in the wake of a model wind turbine

Abstract

The structure of flow turbulence, measured experimentally, in the wake of a model wind turbine is investigated here through higher order scale-dependent statistics of the velocity increments and compared to the smooth wall turbulent boundary layer (base flow) case. The wind turbine wake flow is observed to possess higher turbulent kinetic energy, when compared to the base flow, though it contains more homogenized scale-dependent velocity increments, as confirmed via magnitude cumulant analysis of the streamwise velocities. Along with a reduction in intermittency (a measure of inhomogeneity) in the wake of the wind turbine, the asymmetry of the probability density functions of the velocity increments is also observed to be reduced. This is interpreted in terms of scale decoupling mechanisms and attenuating interactions and non-local energy transfer. In other words, wind turbines reduce the intermittency and asymmetry in the wake flow by breaking and/or deflecting the large-scale flow structures of the incoming flow, thus rendering the structure of the velocity fluctuations more homogenized as compared to the base flow. Experiments were conducted in a large scale, boundary layer wind tunnel at the St. Anthony Falls Laboratory.