Experimental investigation of a jet impinging on a ground plane in crossflow

Abstract

An experimental investigation has been conducted in a wind tunnel to model the impingement of high-velocity jet exhaust flow on the ground, as encountered by V/STOL aircraft. A constant jet velocity was maintained while varying the wind tunnel crossflow velocity, upstream boundary-layer thickness, and height from the ground to the jet exit plane. The radial wall jet, when interacting with the crossflow, forms an oscillating horseshoe-shaped separation bubble, commonly referred to in the literature as a ground vortex. The streamwise distance of the separation point from the jet impingement point is documented here as a function of the flow parameters and geometry. Flow visualization of the flowfield and two-component laser Doppler velocimeter measurements taken through the separation bubble indicate that the separation bubble is highly unsteady and nonsymmetric. This unsteadiness may be related to shear-layer vortices shed from the lip of the jet. Thickening of the upstream boundary layer on the ground plane caused the wall jet to penetrate further upstream. The addition of a large plate flush-mounted to the jet exit caused the ground vortex to move downstream and also decreased the size of the ground vortex.