CFD Analysis of the Performance of an H-Darrieus Wind Turbine Having Cavity Blades

Abstract

Straight-blade vertical axis wind turbines (VAWT) have the ability to exhibit self-starting features and improved aerodynamic performance in the built environment for significant wind speed conditions. But in low wind speeds, such turbines realize several constraints for improved performance in terms of various parameters like blade design, blade shape, solidity, tip speed ratio (TSR), thickness-to-chord ratio and others. Therefore, the motivation behind the present work is the need for performance improvement of H-Darrieus VAWT in the built environment, which has characteristically low wind speed. Cavity shapes on the airfoil surface might cause local flow acceleration leading to suppression of boundary layer separation, which might enhance VAWT’s aerodynamic performance. In this paper, an attempt is made to investigate the effect of circular cavity shape on VAWT’s aerodynamic performance. Cavities have been formed on NACA 0021 airfoil based H-Darrieus VAWT. A CFD study is carried out to understand the inherent flow physics of the turbine. Results showed that there is a significant improvement in starting characteristic of the turbine at wind speeds 5 and 6 m/s having cavity on pressure side. The optimal tip speed ratio for the H-Darrieus turbine has been obtained as 1.3 for which the considered NACA 0021 blade turbine shows maximum power coefficient of 0.16.