Ground vortex formed by impinging jets in crossflow

Abstract

The flowfields associated with single and twin jets impinging in crossflows have been studied experimentally using ground plane pressure profiles and flow visualization. The following parameters and their effect on the position of the ground vortex have been investigated: crossflow-to-jet velocity ratio, crossflow boundary-layer thickness, nozzle height, nozzle pressure ratio, vector angle, and nozzle splay with both fixed and moving ground planes. Results show that the ground vortex moves away from the nozzle centerline as crossflow-to-jet velocity ratio is decreased; the rate of change of position, however, depends on other parameters. This article presents an analysis of this experimental data which isolates the effects of these individual parameters. Nozzle pressure ratio is seen to influence ground vortex position independently of velocity ratio, but the definitions of jet equivalent velocity and crossflow velocity ratio are shown to be important. The effect of the moving ground plane is to reduce vortex penetration significantly; this suggests that a moving ground plane simulation (or moving model) is essential when testing design configurations in ground effect in wind tunnels. With twin nozzles there is a distinct effect of nozzle height on the upstream extent of the ground sheet, especially when the nozzles are toedin. It is suggested that the twin nozzle height effect is connected with jet merging. It is also argued that rig design can produce a blockage effect which moves the ground vortex significantly and can change other apparent parametric effects.