Structure of a supersonic jet with varied geometry of the nozzle entrance

The structure of a supersonic underexpanded low-pressure-ratio jet exhausted from a nozzle with variable geometry of the entrance section is experimentally studied. Total pressure distributions in the initial cross sections of the examined jets are obtained. Based on these distributions, the coordinates of the mixing-region boundaries are found. The curvature of streamlines in the mixing layer within the first two barrels of an underexpanded jet is determined. A dependence generalizing the measurement results on the curvature of streamlines in the first barrel of a weakly underexpanded jet is obtained in dimensionless coordinates.