Abstract
We perform an inviscid, spatial stability analysis of supersonic, heated round jets with the mean properties assumed uniform on either side of the jet shear layer, modelled here via a cylindrical vortex sheet. Apart from the hydrodynamic Kelvin-Helmholtz (K-H) wave, the spatial growth rates of the acoustically coupled supersonic and subsonic instability waves are computed for axisymmetric conditions (m=0) to analyse their role on the jet stability, under increased heating and compressibility. With the ambient stationary, supersonic instability waves may exist for any jet Mach number M(j) ≥2, whereas the subsonic instability waves, in addition, require the core-to-ambient flow temperature ratio T(j) /T(o) >1. We show, for moderately heated jets at T(j) /T(o) >2, the acoustically coupled instability modes, once cut on, to govern the overall jet stability with the K-H wave having disappeared into the cluster of acoustic modes. Sufficiently high heating makes the subsonic modes dominate the jet near-field dynamics, whereas the supersonic instability modes form the primary Mach radiation at far field.