(P19) Computations of dynamic stall in crossflow turbines

Cross-flow turbines rotate on an axis perpendicular to oncoming flow and have advantages such as ability to operate in shallow waters at low tip speeds. Periodic variation of the angle of attack and the resulting flow separation and reattachment on the turbine blades, known as dynamic stall, often causes a loss of torque generation. Reynolds-averaged Navier-Stokes (RANS) computations are complemented with high-fidelity large-eddy simulations (LES) to understand the dynamic stall mechanism at moderate Reynolds numbers. The RANS computations provide a good estimate of forces and power generation for the turbine with a quick turn-around time, especially for configurations that do not involve high angles of attack. The LES computations that have a higher computational cost, are used to analyze the flow separation and vortex dynamics with high detail and to validate the RANS computations. The comparison highlights differences such as premature shedding of the leading edge vortex in the two-dimensional RANS computations and a more chaotic separation region in the LES. By controlling the kinematics, the dynamics of the stall vortex can be manipulated and leads to an increase in power generation.