Physical and Numerical Experiments on an Under-Expanded Jet

Abstract

The axial characteristics of axisymmetric under-expanded sonic jets are dealt with, both experimentally and numerically. Experiments were carried out in a test rig where a sonic nozzle discharged into an ambient which could be kept at different pressures. The density measurements were taken by means of a differential interferometer. The numerical simulation was obtained by adapting a code by Bird (1994) which is based on the MonteCarlo method. The comparison between experimental data and numerical results was carried out by considering the density distribution along the axis of the jet. The direct simulation was then applied to explore the jet characteristics in a rather wide range of the dimensionless products upon which the phenomenology depends. New expressions are presented for the density distribution along the jet axis and for the location of the Mach disk.