Studies on Microjet Control Effectiveness in High-Temperature Supersonic Impinging Jets

Abstract

This study examines the influence of jet temperature on the impinging jet flowfield and compares the effectiveness of microjet control for a Mach 1.5 ideally expanded jet. The tests were performed on a 36.2-mm-diam jet of air, heated to stagnation temperatures up to 1200 K. The jet impinged normally onto a traversable ground plane oriented between 1.5 and 12 throat diameters from the nozzle exit. Findings indicate that the impingement tones persist and generally become more prominent at higher temperatures, and the lift loss levels increase. Microjet injection produced substantial reductions of overall noise levels and considerable lift recovery, although the effectiveness is slightly lower for elevated jet temperatures. In the nozzle-to-ground range resulting in the highest pressure fluctuation levels on the lift plate, reductions reached 9 dB for the 1200 K jet and 10 dB for the cold jet. There was consistent behavior regarding the suppression of near-field and far-field overall sound pressure levels, with maximum reductions for the 811 K jet of 7 and 8 dB, respectively. The lift loss at small nozzle-to-ground distances for elevated jet temperatures increased by up to 30% compared to the cold jet, and microjets were able to reduce lift loss by as much as 34% for the 811 K jet.