Design Optimization of a Vertical Axis Water Turbine with CFD

Abstract

This study presents two-dimensional and three-dimensional numerical simulations of a cross-flow vertical-axis marine current turbine (straight-bladed Darrieus type) with particular emphasis on rotor-performance prediction and hydrodynamic characteristics. Numerical investigations of a model turbine (torque coefficient, power coefficient, tangential force coefficient, normal force coefficient and flow behavior) were undertaken using developed computational models. Turbine design was studied using a time-accurate Reynolds-averaged Navier–Stokes (RANS) commercial solver (ANSYS-CFD). A physical transient rotor–stator model with a sliding mesh technique was used to capture change in flow field at a particular time step. A shear stress transport k-ω turbulence model was used to model turbulent features of the flow. Two-dimensional simulations were employed to test the influence of the profile type and thickness not only in the output power coefficient of the turbine but also on the radial force over the turbine shaft, while three-dimensional simulations were used to compute the curve of power coefficient versus tip speed ratio. Moreover, several flow phenomena as the interference between blades and detached tip vortices and the development of von Karman vortices are identified in the simulations. These phenomena are the reason for the decrease of power coefficient in the three-dimensional case regarding the two-dimensional situation.