Publications

Vertical-axis wind turbine steady and unsteady aerodynamics for curved deforming blades

Moore, Kevin R.; Ennis, Brandon L.

With interest resurging in vertical-axis wind turbines, there is a need for a fast and accurate vertical-axis turbine aerodynamics model. Although 3-D vortex methods are faster than 3-D computational fluid dynamics, they are orders of magnitude slower than required for design optimization. Lower fidelity models like actuator cylinder and double multiple streamtube are popular choices. However, both original formulations assume a steady-state infinite cylinder of unchanging radius, uncharacteristic of offshore turbines. Although stacks of cylinders can be used to approximate curved blades, this yields errors in excess of 50% and does not capture active deformation. Despite current consensus that these are errors inherent to the 2-D formulation, we show the error can nearly all be resolved by including considerations for curved blades. Unsteady effects have historically been captured using a first-order filter on the steady-state induced velocities. Although active deformation can be captured with proper discretization, the unsteady model requires a full revolution solution at each timestep. We found that with a rotating point iterative approach, only solutions at the blade positions are required, which gives a 5-10x speedup. These modifications together enable full-turbine unsteady simulations with accuracy comparable to vortex methods, but as much as 5000x faster.