The far wake of porous disks and a model wind turbine: similarities and differences assessed by hot-wire anemometry

The wakes of two different porous disks have been evaluated experimentally. Such disks are commonly used as physical actuator disk analogs for wind turbines. One disk is made of a uniform wire mesh, while the other has a nonuniform design with radial spars connected by rings. The disks have the same solidity and produce approximately the same drag. The wakes have also been compared to the wake of a model wind turbine and a solid disk. In contrast to earlier studies, the far wake, up to 30 diameters downstream, is included in the comparison. In the near wake, the velocity deficit and turbulence intensity profiles of the disk wakes differ significantly. High levels of turbulence intensity in the wake of the nonuniform disk increase the transverse transport in the wake, which leads to faster spreading and lower velocity deficits in the far wake, compared to the uniform disk and the wind turbine. High velocity gradients in the wake of the uniform disk give rise to turbulence production farther downstream, maintaining higher turbulence levels in the far wake. In addition, coherent vortex shedding is only identified in the wake of the nonuniform disk. None of the disks were able to replicate the asymmetric features of the wind turbine wake. Nonetheless, the results highlight important flow physics that should be considered in the design process of a porous disk used as a wind turbine surrogate.