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A horseshoe-shaped vortex, known as a wing-body junction vortex or horseshoe vortex, forms when spanwise vorticity in the boundary layer along a surface wraps around a wing protruding from the surface. In the past, various techniques of suppressing the wing-body junction vortex have been attempted. Reported here is a novel approach whereby the oncoming wall boundary layer is removed by suction along the body surface immediately upstream of the wing. The idea is that elimination of the boundary layer essentially removes the spanwise vorticity, and inhibits the formation of a wing-body junction vortex. To test this concept experimentally, velocity data were acquired via five-hole probe surveys in a plane normal to one of the walls of a semi-infinite symmetrical airfoil. Differentiation of these data yielded mean stream wise vorticity contours and values of net circulation. In the unmodified (no suction) case, the streamwise leg of the horseshoe vortex was clearly identified. The addition of suction successfully reduced the size and circulation of the large scale vortex. In fact, at a suction volumetric flow rate of about twice that through the boundary layer, the large scale horseshoe vortex could no longer be found for our configuration. Nomenclature Q bl= boundary-layer volumetric flow rate Q s = suction volumetric flow rate Q* = nondimensional suction volumetric flow rate = QJQ H

In many cases, cavitation disappears at higher pressures than those at which it first appears. A measure of this cavitation hysteresis is the cavitation-delay time which tends to decrease with an increase in velocity, size, dissolved air content, or liquid tension. Cavitation hysteresis is a random phenomenon and is also dependent upon flow history and surface characteristics. Liquid tensions of one atmosphere are quite common and tensions of two to three atmospheres may be sustained for several seconds.

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