Aerodynamic Modeling of Swept-Bladed Vertical Axis Wind Turbines

A computationally light time- and space-accurate two-dimensional free vortex model capable of simulating straight- and swept-bladed vertical axis wind turbines operating in a fluctuating wind has been developed. Fast solution times are achieved via vortex merging, limiting the number of calculations necessary at each time step, while solution integrity is maintained through the use of second-order time stepping, vortex-blob rediscretization, and the use of a "vortex curtain" preventing vortex mergers within a predetermined distance from the rotor. Finite span and spoke drag corrections are applied to account for three-dimensional effects in addition to a formulation for extending the two-dimensional model to arbitrary three-dimensional geometries. The two-dimensional free vortex model is validated against unswept and swept-bladed vertical axis wind turbine experimental data, with allowances for the effects of wind-tunnel walls made within the free vortex model in the case of the swept-bladed data set.