Improvements to the Actuator Disk Concept for Modelling Horizontal Axis Wind Turbines*

The present study validates design improvements to the actuator disk wind turbine model at high Reynolds numbers through experimental comparisons of the wakes of a horizontal axis wind turbine and matched porous disks. The experiments are conducted in the High Reynolds Number Test Facility at Princeton University, where diameter-based Reynolds numbers on the order of one million are achieved at low velocities using pressurized air as the working fluid. The rotor and disks are matched based on conventional metrics; the Reynolds number and thrust coefficient, in addition to matching rotor length scales and radial solidity profile. Wake hot-wire measurements reveal a near perfect match to the rotor in terms of mean streamwise velocity deficit can be achieved at distances as close as 1 diameter downstream by matching the radial solidity profile, a significant improvement over the 5 to 6 diameter distance of previous models. Furthermore, by matching disk features to the length scale of the rotor's tip chord length, the amplitude of the turbulent fluctuations throughout the disk wake can be matched to the rotor, again improving over previous models. However, specific wakes features, such as the rotor tip vortex, are notably absent.