The Mechanism of Ventilation Inception on Surface Piercing Foils

Abstract

Either separation or cavitation is a necessary but not sufficient condition for ventilation inception, and the surface ‘seal’ must be ruptured in some way to admit air. Three modes of rupture have been observed; at the nose, at the trailing edge, and through the tip vortex. Nose ventilation is associated with the vortex in a separation bubble, and tail ventilation arises from the instability of surface perturbations and can be predicted empirically. Tip vortex ventilation is not likely on prototype craft. Waves increase the likelihood of ventilation and in open sea conditions a reduction of some 4° in inception angle is predicted. Conventional fences suppress nose ventilation only.