High Reynolds number wind turbine experiments in the Variable Density Turbulence Tunnel

Wind turbines operate at high Reynolds numbers that are challenging to reproduce in controlled laboratory settings. Therefore, experiments are often conducted on scaled-down turbine models at vastly reduced Reynolds numbers. However, a change in the Reynolds number changes the nature of the turbulence and can thus affect both the blade-level aerodynamics and the evolution of the wake. Traditional wind tunnels increase the Reynolds number by increasing the velocity, but this reduces the tip speed ratio. In order to maintain reasonably high tip speed ratios, unrealistically high rotational rates are then needed. Here, we present a new experimental setup that is being developed in the Variable Density Turbulence Tunnel (VDTT) at the Max Planck Institute for Dynamics and Self-organisation. This wind tunnel uses pressurized SF6 to achieve Reynolds numbers on the order of Re_D = 10^7 on a small-scale turbine. Because the VDTT achieves high Reynolds numbers at low velocities, high tip speed ratios can be achieved at reasonable rotation rates. Lagrangian particle tracking allows for extended wake studies. An active grid will be used to alter the inflow turbulence intensity.