Planar velocimetry of jet/fin interaction on a full-scale flight vehicle configuration

Stereoscopic particle image velocimetry has been implemented in a production-scale transonic wind tunnel for studying jet/fin interaction created by exhaust plumes from spin rockets on a full-scale model of a finned body of revolution. Data acquired just upstream of the leading edge of the fin root clearly display the counter-rotating vortex pair that dominates the interaction far field and the remnant of the horseshoe vortex near the vehicle surface. The counter-rotating vortex pair is distinctly asymmetric due to originating from a scarfed nozzle and displays some rotation with respect to the model surface. Velocity fields measured over a range of flowfield conditions and model orientations show that the vortex of negative sign is always closer to the fins than its positive counterpart and does not greatly change location as flowfield parameters are altered. The circulation of this vortex correlates with a reduction in the simultaneously measured vehicle roll torque. Further correlations are hindered by untreatable bias errors in the velocimetry. Instead, a model of the vortex structure derived from the velocimetry data reveals that the angle of attack induced upon the fins by the counter-rotating vortex pair correlates with the roll torque loss. Similar correlations suggest that in level flight this effect is dominant, but at angle of attack the horseshoe vortex on the windward side has an additional influence.