Aeroacoustics and Background Oriented Schlieren of a Jet-Forebody Assembly

A supersonic counterflowing jet (CFJ) provides thrust opposite freestream flow encountered by a body traveling at supersonic/hypersonic speeds. One principal aim of a CFJ is to create a larger perceived body and displace bow shocks further from the body, leading to reduced drag and aerodynamic heating, thereby reducing the weight of current ablative heat shielding on reentry vehicles. Additionally, CFJs show promise as means for attitude control during hypersonic descent of atmospheric reentry.

This investigation focuses on the structure of a supersonic round jet mounted to a blunt fore body and exhausting into quiescent atmosphere by comparing jet flow with and without the forebody. Acoustic and forebody pressure fluctuations were also measured. The jet structure was investigated using Schlieren and Background-Oriented Schlieren. A round jet with exit-to-throat area ratio Ae/Ath near 4 was operated in subsonic, over-expanded and under-expanded regimes. The results from this study serve as a baseline for supersonic wind tunnel experiments with a CFJ test article. The forebody affects jet structure. The results reveal strong oscillations in the jet structure whose frequency correlates with the pressure fluctuations on the forebody surface. The fundamental frequency of the pressure fluctuations on the forebody decreases with increasing mass flow rate through the jet.

Understanding these interactions provides crucial input to the design of a CFJ control system based on in-flight acoustics readings.