TIP VORTEX ROLL-UP AND CAVITATION

Experiments conducted in three cavitation tunnels with elliptical planform hydrofoils, of area ratio 3.8 and mid-span chord ranging from 40 to 475 mm, allowed the investigation of the effects of Reynolds numbers, between 4x105 to 6.8x106, on tip vortex cavitation. The hydrodynamic forces of the hydrofoil were measured for Reynolds numbers ranging from 2.5x105 to 2.4x106. The tangential velocity profiles were measured in each one of the cavitation tunnels for numerous stations situated between the tip of the foil and the trailing edge at mid-span and some other stations beyond the trailing edge. Axial velocities and turbulence levels were also measured. The critical cavitation numbers were determined in the two largest cavitation tunnels. From the values of the tangential component of the velocity, the local intensity of the vortex and the radius of the inner, solid body rotation region are determined. Using their values at the position corresponding to the minimum pressure along the vortex path, the minimum pressure coefficient is computed and its absolute value compared to the desinence cavitation number for several flow situations. This comparison is very satisfactory and sheds new light on tip vortex cavitation interpretation.