Supersonic jet mixing in the presence of two annular co-flow streams

Abstract

The mixing characteristics of a Mach 1.9 jet at three levels of overexpansion, corresponding to nozzle pressure ratio (NPR) 3, 4 and 5, in the presence of a sonic co-flow (secondary flow), which was submerged in a subsonic co-flow (tertiary flow) was studied experimentally. For these NPRs the secondary co-flow is sonic with underexpanded levels and the tertiary flow Mach number was found to be 0.41, 0.71 and 0.85, respectively. The centerline decay results of the primary jet show that the jet mixing is abated by the co-flow, at all levels of expansion. However, in spite of the reduced mixing encountered by the supersonic primary jet, the waves in the jet core are found to be weaker in the presence of co-flows. This may be regarded as an advantage from the shock associated noise point of view, in accordance with Tam’s theory; which states weaker the waves in the core, the lesser is the shock associated noise. The results show that the reduced mixing environment caused by the sonic co-flow alone leads to the jet core elongation of about 20%, 23% and 49%, at NPRs 3, 4 and 5, respectively. The core length of the jet is found to increase by 29%, 46% and 62%, respectively, at NPRs 3, 4 and 5, when both sonic and subsonic co-flow streams are present.