Effect of background turbulence on the wakes of horizontal-axis and vertical-axis wind turbines

We report a wind tunnel study on the wake generated by a horizontal-axis (HAWT) and a vertical-axis wind turbine (VAWT). Two scaled models, one of each type, have been tested in a wind tunnel, under low blockage and at Reynolds numbers, based on the rotor diameter $D$, of $R{e}_D=265\times 10^3$ for the HAWT and $330\times 10^3$ for the VAWT. The models scale with respect to the largest commercially deployed turbines is of 1/383 and 1/65.5, for the HAWT and the VAWT, respectively. Furthermore, two different inflows were tested: low and moderate turbulence conditions. For each type of turbine and inflow, different values of tip-speed ratio and $R{e}_D$ were tested.

Hot-wire anemometry was used to characterize the wake at different streamwise positions, exploring the range $1<x/D<30$ for the HAWT and $1<x/D<15$ for the VAWT.

We find that, under a low-turbulence inflow, both turbines generate significantly different wakes, characterized by the velocity deficit, wake width and the profiles of average and rms streamwise velocities. More specifically, in low-turbulence conditions, the VAWT presents faster recovery than the HAWT. Remarkably, we observe that a moderately turbulent inflow results in similar wake shapes for both turbines, presenting similar recovery and structure under all studied conditions.