Hydrofoil Roughness Effects on von Kármán Vortex Shedding

The shedding process of the von Kármán vortices is shown to be highly related to the state of the boundary layer over the entire hydrofoil: The selected hydrofoil has a laminar-turbulent boundary layer transition at mid-chord for an incidence angle of 0° and tested Reynolds number range. With the help of a distributed roughness, the transition to turbulence is triggered at leading edge. The vortex shedding frequency and the vortex-induced vibration are compared For the two roughness configurations. Cavitation is used as a mean of visualization of the wake flow: Since vortex-induced vibration and high speed visualization are synchronized, the hydrofoil vibration level is considered versus the vortex span-wise organization. The occurrence of the 3D structures of shed vortices and the modulation of the vortex-induced vibration signals are investigated.