An investigation of the Mach disc and the Riemann wave formation in impulsive jets

An experimental investigation is carried out of the shock waves in nonstationary jets of shock-heated N2, Ar, and CO2 outflowing from flat and axisymmetrical sonic nozzles. The ratio of the pressure behind the reflected shock wave to the pressure in the vacuum chamber ranges from 20 to 200 in the study. Schlieren photographs for the nonstationary jet structure are obtained for different spatial orientations of the flat nozzle using a particular Schlieren apparatus and a spark light source. The nonstationary wave structure of the flow is reproduced on the basis of the obtained Schlieren photographs of jet formation. The geometrical characteristics of the nonstationary Riemann wave for three nozzles and different values of n are generalized in dimensionless similarity parameters. A dependence is obtained between the location of the Mach disk and the time up to the stationary location. A comparison is made with the calculation, and an analysis is performed for the acceptance of the model of a source suddenly introduced into flow being investigated.