Performance-scaled rotor design method for model testing of floating vertical axis wind turbines in wave basins

Abstract

The wave basin model tests of floating wind turbines typically follow the Froude scaling law, where a geometric-scaled rotor cannot achieve the target thrust due to the Reynolds-number scaling effect. To tackle this issue, a performance-scaled rotor (PSR) has been successfully used in the wave basin model testing of floating horizontal axis wind turbines (HAWTs). Unlike HAWT, the thrust and side forces of a vertical axis wind turbine (VAWT) present periodic and large amplitude variations with the azimuth angle. In this study, a novel PSR design method is proposed for the model testing of floating VAWTs. An alternative airfoil with good aerodynamic performances at low-Reynolds-number is selected to replace the original one. The relationship between the thrust coefficient and the chord length is derived analytically, with accuracy-enhancing corrections. The chord length of the PSR is then determined. The method and procedure are demonstrated by designing and testing a PSR of a 5 MW floating VAWT with three straight blades and a scale ratio of 1:50. Thrust and lateral forces of the floating VAWT are compared and analyzed. Results indicate that the designed PSR can reproduce the thrust and side forces and is applicable for model testing of floating VAWTs.