Two-dimensional laser-induced thermal ablation modeling with integrated melt flow and vapor dynamics

A new detailed, physics-based computational framework for the direct prediction of material ablation under nanosecond pulsed laser irradiation is presented. The framework, named directed energy illumination and visualization (DEIVI), integrates two-dimensional (axisymmetric) models for the following physical processes within a single framework for the first time: (i) coupling of the laser irradiation with the solid, (ii) transient heat conduction in the condensed (solid and melt) phases including melt front tracking, (iii) flow of the melt layer under the action of recoil pressure, (iv) vaporization of the melt and development of recoil pressure, and (v) dynamics of the vapor/gas. The solution for transient heat conduction and melt interface tracking using the enthalpy method is similar to the development by Ho et al. [J. Appl. Phys. 78, 4696-4709 (1995)]; however, they did not model the flow of the melt layer and modeled one-dimensional heat flow in the solid. To model the melt flow, DEIVI solves the incompressible, viscous Navier-Stokes equations that include a pressure correction solver, treatment of spatial derivatives using upwind or hybrid schemes, and a staggered grid. The compressive interface capturing scheme for arbitrary mesh volume of fluid method [O. Ubbink, Ph. D. thesis, University of London (1997)] is implemented for tracking the melt/vapor interfaces. The recoil pressure is applied by setting a fixed-pressure boundary condition in grid cells located at the melt-vapor interface. Surface tension is also included in order to ensure realistic surface morphology behavior at the melt-vapor interface. The vaporization process is treated using a quasiequilibrium convection-dominated approach combined with Knudsen-type jump conditions [S.I. Anisimov, Sov. Phys. JETP 27, 182-183 (1968) and C. J. Knight, AIAA J. 17, 519-523 (1979)] to obtain the input conditions for solving the two-dimensional (axisymmetric) gasdynamics equations for the vapor. An operator splitting procedure is used to solve the Euler equations using a Lax-Wendroff or Colella and Woodward [J. Comput. Phys. 54, 174-201 (1984).] piecewise parabolic scheme. This paper presents key aspects of the integrated framework as well as verification analyses performed to ensure the accuracy of individual modules. (C) 2017 Laser Institute of America.