Instability of Astrophysical Jets. II

Abstract

Lateral oscillations of choked underexpanded rectangular jets with a large aspect ratio are observed experimentally. We compare the experiments with the results of our numerical simulations of two-dimensional slab jets. A time-dependent technique of solution is applied to solve the Euler equations for a compressible ideal gas. The numerical results show that the jet does not oscillate laterally when the symmetric boundary condition is applied. On the other hand, the self-sustained asymmetric oscillation of the jet occurs under the asymmetric boundary condition. When an asymmetric jet oscillation appears in the computed domain, it continues even after the asymmetric boundary condition was replaced by the symmetrical ones. The oscillation of the supersonic jet is self-sustained. This is probably because of the feedback loop consisting of the sound waves propagating towards the nozzle exit and the coherent structures convected with jets.