Separation Control of Aero Boundary Layer in Supercavitating Bodies and Its Effect on Pressure Drag Reduction

Abstract

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. In fact such methodologies consider cavitation flow statically, rather than taking dynamic effects of overall flow into account. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Thereby, in order to configure the system conditions which may be cause of cavity perturbation and so system oscillation, we need to use proper methodologies in which turbulence shear stress effects and role of their distribution, are suitably come into account. Numerical simulation of supercavitating flows is pursued in this paper. The effect of air injection in the cavity as a means of stabilization is examined. A k-epsilon model is employed for the liquid flow region while a single-fluid two phase model is applied in the cavity region. Comparisons of several conditions exhibits that at very low cavitation numbers, constant pressure assumption fails particularly for gradient shaped profiles and separation is probable if the flow is sufficiently turbulent. Air injection into the NATURALLY FORMED supercavity is found as an effective way to prevent the probable separation and so significant pressure drag reduction up to 70% is observed. In addition, the position of injection plays a major role to control the aero boundary layer and it has to be considered.