Computational Study of a Small Scale Vertical Axis Wind Turbine (VAWT) : Comparative Performance of Various Turbulence Models

Abstract

The paper presents a numerical approach to study of fluid flow characteristics and to predict performance of wind turbines. The numerical model is based on Finite-volume method (FVM) discretization of unsteady Reynolds-averaged Navier- Stokes (URANS) equations. The movement of turbine blades is modeled using moving mesh technique. The turbulence is modeled using commonly used turbulence models: Renormalization Group (RNG) k- turbulence model and the standard k- and k- turbulence model. The model is validated with experimental data over a large range of tip-speed to wind ratio (TSR) and blade pitch angles. In order to demonstrate the use numerical method as a tool for designing wind turbines, two dimensional (2-D) and three-dimensional (3-D) simulations are carried to study the flow through a small scale Darrieus type H-rotor Vertical Axis Wind Turbine (VAWT). The flows predictions are used to determine the performance of the turbine. The turbine consists of 3- symmetrical NACA0022 blades. A number of simulations are performed for a range of approaching angles and wind speeds. This numerical study highlighted the concerns with the self-starting capabilities of the present VAWT turbine. However results also indicated that self-starting capabilities of the turbine can be increased when the mounted angle of attack of the blades is increased. The 2-D simulations using the presented model can successfully be used at preliminary stage of turbine design to to compare performance of the turbine for different design and operating parameters, whereas 3-D studies are preferred for the final design.