Wake Recovery of Vertical-Axis Wind Turbines: Effects of Rotor Solidity and Reynolds Number

Abstract

The wake evolution of vertical-axis wind turbines (VAWTs) plays a critical role in turbine-array performance, yet the wake variations associated with rotor geometry, operating condition, and Reynolds-number-related factors remain insufficiently understood. In this study, the wake characteristics of H-type VAWTs were systematically investigated under varying rotor diameters (D = 2, 3, 4 m), chord lengths (c = 0.1–0.4 m), and incoming wind speeds (v∞ = 6–10 m/s) using a two-dimensional mid-span CFD approach based on Improved Delayed Detached Eddy Simulation (IDDES) built on the SST k-ω model. The simulations are intended to examine mid-span wake mechanisms rather than to directly predict full three-dimensional far-wake recovery, turbine-array interaction, or engineering layout performance involving tip vortices, spanwise momentum transport, and three-dimensional breakdown of coherent structures. The results show that, for the selected reference geometry and within the tested inflow-speed range, the lateral mean-velocity profiles at the same downstream location collapse reasonably well after normalization by v∞ and D, indicating weak sensitivity to incoming wind speed under these conditions rather than general Reynolds-number independence of VAWT wakes. For cases with different solidities, the observed wake differences should be interpreted as the combined effects of rotor solidity and the corresponding near-optimal operating condition. Overall, this study provides a mechanism-oriented numerical assessment of wake behavior in H-type VAWTs.