Stability and Transition of the Wake of a Hydrokinetic Axial-Flow Turbine

A Large-Eddy Simulation study is reported on the wake generated by the rotor of an axial-flow hydrokinetic turbine. The resolution of the computational grid, composed of about 1.9 billion points, enabled us to capture in detail the phenomena of instability of the tip vortices, including long-wave and short-wave instabilities and mutual inductance. We found that these phenomena trigger the process of wake recovery, starting when the coherence of the tip vortices is lost. This allows the free-stream momentum to penetrate into the wake core via both radial inward flows and turbulent mixing.