Full self-similar solutions of the subsonic radiative heat equations

Abstract

We study the phenomenon of diffusive radiative heat waves (Marshak waves) under general boundary conditions. In particular, we derive full analytic solutions for the subsonic case, that include both the ablation and the shock wave regions. Previous works in this regime, based on the work of [R. Pakula and R. Sigel, Phys. Fluids. 443, 28, 232 (1985)], present self-similar solutions for the ablation region alone, since in general, the shock region and the ablation region are not selfsimilar together. Analytic results for both regions were obtained only for the specific case in which the ratio between the ablation front velocity and the shock velocity is constant. In this work, we derive a full analytic solution for the whole problem in general boundary conditions. Our solution is composed of two different self-similar solutions, one for each region, that are patched at the heat front. The ablative region of the heat wave is solved in a manner similar to previous works. Then, the pressure at the front, which is derived from the ablative region solution, is taken as a boundary condition to the shock region, while the other boundary is described by Hugoniot relations. The solution is compared to full numerical simulations in several representative cases. The numerical and analytic results are found to agree within 1% in the ablation region, and within 2 − 5% in the shock region. This model allows better prediction of the physical behavior of radiation induced shock waves, and can be applied for high energy density physics experiments.

Self-similar Solution of the Subsonic Radiative Heat Equations Using a Binary Equation of State

“…In the section we briefly repeat the methodology of obtaining and patching two self-similar solutions in order to describe the whole solution (for details see [13]). The ablation region is solved using a time-dependent temperature boundary condition, in a manner similar to [7], and the shock region is solved using a time-dependent pressure boundary condition.…”

“…The small box in the velocity graph shows a close-up of the shock region. The figure is taken from [13].…”

“…1 describe three variables P ,V and u. In order to obtain self-similarity, we must also assume that the density diverges at the front of the solution (for further discussion see [13]), which makes the solution applicable only for the ablation region.…”

“…Recently, Shussman and Heizler proposed a semi-analytic model to describe both ablation and shock regions [13]. The solution is composed of two different self-similar solutions, one for each region.…”

“…This paper proceeds as follows: In Sec. II we briefly present the model and the governing equations, which were introduced widely in [13], only now using a binary-EOS. In Sec.…”