Vortex cavitation can appear in the wake flow of hydrofoils, inducing unwanted consequences such as vibrations or unstable behaviors in hydraulic machinery and systems. To investigate the cavitation effects on hydrofoil vortex shedding, a numerical investigation of the flow around a 2D NACA0009 with a blunt trailing edge at free caviation conditions and at two degrees of cavitation developments has been carried out by means of the Zwart cavitation model and the LES WALE turbulence model which permits predicting the laminar to turbulent transition of the boundary layers. To analyze the dynamic behavior of the vortex shedding process and the coherent structures, two identification methods based on the Eulerian and Lagrangian reference frames have been applied to the simulated unsteady flow field. It is found that the cavitation occurrence in the wake significantly changes the main vortex shedding characteristics including the morphology of the vortices, the vortex formation length, the effective height of the near wake flow and the shedding frequency. The numerical results predict that the circular shape of the vortices changes to an elliptical one and that the vortex shedding frequency is significantly increased under cavitation conditions. The main reason for the frequency increase seems to be the reduction in the transverse separation between the upper and lower rows of vortices induced by the increase in the vortex formation length.
Effects of non-uniform permeability on vortex shedding and noise control of blunt trailing edge
