Structure of low-density supersonic jet

Abstract

The results presented in this paper from an experimental study of the structure of a supersonic air jet for different discharge conditions 10 -< n -< 104, 1.15 -< M a <- 3.3, 10 -4-< K, = k./d. <- 10 -3, where M a is is the Mach number at the nozzle exit, k. is the molecular mean free path at the nozzle critical section, d, is the nozzle critical section diameter, and n is the ratio of the nozzle exit pressure to the ambient pressure, make it possible to identify the influence of high pressure ratios n, high Mach number M a, and flow rarefaction on the structure of the supersonic underexpanded jet. The Knudsen number K. and the parameter C =K, 4"~'are also used to characterize the flow rarefaction. 1. The experiments were conducted in the low-density wind tunnel described in [8]. The working gas was air, preheated to ~600~ to prevent condensation during adiabatic expansion [9]. The gas jet discharged through a supersonic conical nozzle into a low-pressure chamber. The nozzle dimensions and jet discharge conditions are shown in Table 1, where in column d the upper numeral corresponds to the nozzle throat diameter and the lower numeral is the nozzle exit diameter; ~0 is the nozzle half-angle; in the column M the upper numeral is the Mach number M a' at the nozzle exit, calculated for isentropic expansion of the gas, and the lower numeral is the nozzle exit Mach number, obtained from measurements of the total pressure P0'; and P0 is the adiabatic flow stagnation pressure, in mm Hg. The following parameters were measured in the experiments: pressure P0 and temperature T o in the adiabatically decelerated flow, the total pressure P0', and the vacuum chamber pressure Pt. A Pitot tube of 0~ diam. was used to measure the total pressure. The viscous corrections were introduced in accordance with the technique presented in [8]. The results of the P0, To measurements were used to calculate