An underexpanded supersonic circular jet was studied experimentally in a pressure ratio range of 2–15, yielding an equivalent Mach number range of 1.1–2.4 downstream of the nozzle. Spark Schlieren photography and near‐field pressure measurements showed large changes in the jet structure for different Mach numbers. For nearly sonic exit velocity, the jet had a dominant symmetric structure and spreading rate similar to subsonic conditions. For an exit velocity equivalent to M>1.2, the jet switched mode to a helical structure with an accompanying substantial increase in the spreading rate. A transitional region was determined for 1.12<M<1.18, in which the jet switched modes intermittently from axisymmetric to helical. For Mach numbers higher than 1.6, another structural change was observed, related to the emergence of a normal shock in the first shock cell. The structural changes affected the near‐field pressure fluctuations of the jet. The jet with the helical structure had a strong pressure field component in the upstream direction that could be related to the higher spreading rate of the jet.
[1]
Gunter Hermann,et al.
On the inviscid instability of a circular jet with external flow
,
1982,
Journal of Fluid Mechanics.
[2]
Gerald L. Morrison,et al.
Instability process in low Reynolds number supersonic jets
,
1980
.
[3]
D. R. Glass.
Effects of acoustic feedback on the spread and decay of supersonic jets.
,
1968
.
[4]
A. Powell,et al.
On the Mechanism of Choked Jet Noise
,
1953
.
[5]
Ephraim Gutmark,et al.
Characterization of large-scale structures in a forced ducted flow with dump
,
1985
.
[6]
D. K. Mclaughlin,et al.
Experiments on the instability waves in a supersonic jet and their acoustic radiation
,
1975,
Journal of Fluid Mechanics.
[7]
Anjaneyulu Krothapalli,et al.
Recent advances in aerodynamics
,
1986
.
[8]
Christopher K. W. Tam,et al.
Sound generated by instability waves of supersonic flows. Part 1. Two-dimensional mixing layers
,
1984,
Journal of Fluid Mechanics.