Numerical simulation of gas propagation process behind a shock wave during optical breakdown of air in a cylindrical channel

Abstract

This paper substantiates the need to study processes during nanosecond optical breakdown inside a cylindrical channel, and gives an analogy between L. Sedov’s theory of point explosion and an optical breakdown. A variant of the evolution of a shock wave inside a cylindrical channel is proposed. Based on the solution of the problem of a point explosion with backpressure, a preliminary estimate of the gas pressure and velocity behind the shock front was obtained to set the initial conditions in Ansys Fluent. As a result of numerical simulation, the characteristics of the shock wave were calculated, and the distributions of the velocity, density and pressure of the gas behind the shock front were obtained. According to comparison of the experiments and results of numerical simulation, an estimate of the shock wave energy is given, which is from 8 to 16% of the energy of a nanosecond laser pulse. The results of the proposed method of numerical calculation are consistent with the experimental data for measuring the time of the shock wave exits from the channel and the target momentum at atmospheric pressure.