Numerical modeling and wind tunnel experiments for optimally designed J-VAWT

Abstract Recently, an advanced J-VAWT, featured by blades with a distinctive concave “J” profile, has been proposed. Previous numerical studies have reported varied performance outcomes for J-blades, with some indicating improvements and others showing negligible or negative effects. However, experimental evidence from carefully calibrated wind tunnel tests remains scarce to clarify the controversy. In this paper, the Taguchi analysis is performed to optimize the design of J-blades with the profile NACA0018. In this analysis, three control factors are considered, including the opening ratio, chord length, and blade thickness, for each of which there are five levels. In the optimization process, flow fields were simulated by the software Fluent to obtain the power coefficients of all 2D/3D models. With simply 25 simulation sets, the Taguchi analysis produced an orthogonal array of L25(53) to obtain the optimal design of the J-blades. For verification, both full-scale models of the closed-type and the optimally designed J-VAWT were experimented in a wind tunnel. The experimental results show that the use of J-blade may provide a performance gain of roughly 5% (7%) for Cp (Cm) at relatively low rotational speeds. In addition, the J-VAWT exhibited notably better self-starting capability. The present findings are applicable to small-scale VAWTs in the low-to-moderate Reynolds-number regime.