Flow visualization for a STOVL aircraft in ground proximity

Abstract

Flow visualization experiments in a water tunnel have been conducted to study the interaction of three-dimensional impinging jets for potential STOVL aircraft applications. The test model consisted of a delta wing, a fuselage, two axisymmetric centerline nozzles and two detachable simulated engine inlets. The flow field behavior was studied as a function of model height above a ground plane, jet nozzle spacing, jet exit velocity, angle of attack, and cross flow velocity. The test results showed body and flow field vortex formations, jet interaction effects, jet unsteadiness and a horseshoe shaped ground vortex. At positive angles of attack traditional delta wing leading edge vortices were moved to the lower surface depending on the jet strength and ground proximity. In some cases vortices rotating about an axis normal to the ground plane were observed. These vortices formed near the nozzle exits on the wing lower surface and moved downstream. Under certain conditions these vortices touched down, much like a tornado, before dissipating. The presence of lower surface leading edge vortices, at low heights, suggest the likelihood for strong suckdown effects. Simulated engine inlet operation confirmed the possibility for exhaust reingestion problems at low heights. v