Nonlinear deformations of a radiating shell moving with acceleration

Abstract

The two-dimensional nonstationary motion of a cold dense shell accelerated under the action of rarefied hot gas pressure is modeled. The influence of radiative processes on manifestations of cumulative effects predicted by the inertia model is analyzed. It is assumed that the major medium component is hydrogen with small admixtures of oxygen, nitrogen, carbon, silicon, and iron. Radiative energy loss caused by photorecombinations and excitation followed by impurity ion metastable level deexcitation is taken into account. An approximation to the cooling function is suggested and implemented. This approximation can be used to perform calculations over wide ionization degree and gas temperature ranges. The formation of a shell during gas expansion ionized and heated by a source of ultraviolet radiation is studied. The characteristic time of shell appearance and its gas dynamic parameters are determined. The distribution of plasma temperature is shown to be nonmonotonic and have a maximum close to the ionization front. An increase in small perturbations of the velocity of a shell is shown to cause the formation of radial fibers and the concentration of gas mass and momentum in them. The structure of condensates formed is, however, much more complex than that predicted by the model of a thin layer of incompressible matter. In particular, condensation includes “fingerlike” thickening and a more extended region with a lower density. It also follows from the calculations that radiative cooling contributes to shell expansion in the radial direction but does not change the integral characteristics of condensations substantially.