Experimental and computational investigation of supersonic counterflow jet interaction in atmospheric conditions

The flow field generated by the interaction of a converging-diverging nozzle (exit diameter, D=26 mm M=1.5) flow and a choked flow from a minor jet (exit diameter, d=2.6 mm) in a counterflow configuration was investigated. During the tests both the main C-D nozzle and the minor jet stagnation pressures were varied as well as the region of interaction. Investigations were made in the near field, at most about 2D distance, and in the far field, where the repeated patterns of shock waves were eliminated by turbulence. Both nozzles exhausted to the atmospheric pressure conditions. The flow physics was studied using Schlieren imaging techniques, Pitot-tube, conical Mach number probe, Digital Particle Image Velocimetry (DPIV) and acoustic measurement methods.;During the experiments in the far field the jets interaction was observed as the minor jet flow penetrates into the main jet flow. The resulting shock structure caused by the minor jet's presence was dependent on the stagnation pressure ratio between the two jets. The penetration length of the minor jet into the main jet was also dependent on the stagnation pressure ratio. In the far field, increasing the minor jet stagnation pressure moved the bow shock forward, towards the main jet exit.;In the near field, the minor jet flow penetrates into the main jet flow, and in some cases modified the flow pattern generated by the main jet, revealing a new effect of jet flow interaction that was previously unknown. A correlation function between the flow modes and the jet stagnation pressure ratios was experimentally determined. Additionally the flow interaction between the main and minor jets was simulated numerically using FLUENT. The optimal mesh geometry was found and the k-epsilon turbulence model was defined as the best fit. The results of the experimental and computational studies were used to describe the shock attenuation effect as self-sustain oscillations in supersonic flow.;The effects described here can be used in different flow fields to reduce the total pressure losses that occur due to the presence of shock waves. It will result in better designs of ramjet/scramjets combustors, fighter aircraft inlets and as well as in noise reduction of existing aircraft engines. It can also improve performance of rotating machinery; ramjet fuel injectors and aircraft control mechanisms.