The Effect of a Slat on Boundary Layer Characteristics and Cavitation of the Main Foil

Abstract

It is known that the cavitation is dependent upon the boundary layer characteristics. Therefore, it is considered that cavitation can be controlled by controlling the boundary layer.This paper deals with a SLAT-FOIL combination, main foil and upstream slat. The slat is one of the boundary layer control methods for foil sections.Firstly, the authors designed the SLAT-FOILs to increase the pressure at the laminar separation point as high as possible, and verified the cavitation suppression effect by cavitation tunnel tests.Secondly, the authors studied the interaction between the wake of the slat and the boundary layer on the main foil, and found that when the wake of the slat merged into the boundary layer on the main foil, it accelerated turbulent transition. If the pressure of the turbulent transition point was high enough, the cavitation was remarkably suppressed.In conclusion, two methods of the cavitation control (suppression) can be suggested, those are as follows.1. A slat can change the pressure distribution on the foil. As the result of increase of the pressure at the laminar separation point, the incipient cavitation number of sheet type cavitation can be decreased.2. When a slat is near the foil, the wake of the slat is mixed into the boundary layer on the main foil, which accelerates turbulent transition. If the pressure on the transition point is high enough, the incipient cavitation number is remarkably decreased.