On the Effects of Aero Boundary Layer Control on Pressure Drag Reduction in Supercavitating Bodies

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. 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. Furthermore as we’ll see, pressure distribution on cavity surface caused due to overall conditions, induct nonaxisymetric forces and they may need to be investigated. Primarily we describe how pressure distribution into the cavity can cause separation of the aero boundary layer. Then we present some approaches by which this probable separation can be controlled. 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 delay probable separation and so significant pressure drag reduction is achieved. In addition, the position of injection plays a major role to control the aero boundary layer and it has to be considered. Moreover, electromagnetic forces cause to delay or even prevent separation in high pressure gradient flows and interesting results obtained in this regard shows significant drag reduction in supercavitating vehicles.