Numerical investigation of the use of flexible blades for vertical axis wind turbines

Abstract

This study proposes a novel vertical axis wind turbine (VAWT) design with flexible blades aiming to improve their energy extraction capability. The blade deformation is achieved using Ansys Fluent dynamic mesh and user-defined functions to control the position of the blades nodes at specific azimuthal angles. An optimization study is carried out using computational Fluid Dynamics (CFD) simulations and Design of Experiments (DOE) to get the optimal design parameters of the flexible blade at different Tip Speed Ratios (TSRs). In addition, a comparison between the DOE results of both 2D and 3D CFD simulations is achieved to assess the use of 2D simulations for optimization purposes. Also, a detailed numerical study of the aerodynamic performance of the turbine based on this new design is done to compare the rigid and flexible blade models' power coefficient and flow fields around the blades. Results of 2D and 3D CFD simulations show that the flexible blades are able to improve the power coefficient of the turbine by up to 66% and 32% respectively at low tip speed ratios diminishing gradually with increasing tip speed ratios. It is also noticeable that similar pattern in power coefficient results was obtained from the 2D and 3D simulations of both turbine models. This, in turn, demonstrates the efficacy of 2D simulations in accurately determining optimized design parameters while significantly reducing computational costs compared to 3D simulations.