Experimental investigation of shock wave structure and streamwise vortices in supersonic jet

The results of an experimental study of the three-dimensional flow structure in a supersonic nonisobaric air jet in the range of nozzle Mach number from 1.0 to 4.0 and nozzle pressure ratio from 5.0 to 150 are discussed. Three characteristic types of the streamwise distributions for the amplitudes of spectral components along the jet are revealed. The mentioned types are connected with the decrease of amplitude in the first jet cell, the existence of the maximum of amplitude and a comparatively insignificant variation of the amplitude along the jet. An essential influence of the state of the nozzle boundary layer on the development of streamwise vortex structures in the mixing layer of the initial region of the jet is shown. This influence is manifested as a decrease of the fraction of small-scale streamwise vortices in a shear layer for a jet issuing from the nozzle with a comparatively thick boundary layer. The data on dynamics of the streamwise vortices, in particular, of their secondary instability are also discussed shortly. Some peculiarities related to the forming of the flow separation inside the nozzle are analyzed. A hysteresis phenomenon in the behavior of a number gasdynamic and geometric characteristic of the nozzle flow separation is considered.