Radiation-flux-conservative beam shapes for laser-fluid coupled problems in finite volumes

Abstract

A finite volume code, written in C++, is capable of computing the laser materialprocessing physical phenomena. To explain the whole structure of the light-matterinteraction as a transient process, a detailed numerical solution for the propagation of beams must be provided in the first place.Since we are interested in the molten material’s fluid dynamics, which are modeled on a multiphase volume-of-fluid approach, and the laser physics, paraxiallaser beam models, are coupled with the fluid problem, it is also advantageous to describe the beam propagation using finite volume methods.Due to the fact, that there is a large discrepancy between the necessary grid size for the fluid problem and laser physics, some problems concerning energy conservation can arise. The radiation flux-conservation can affect the numerical stability ofthe absorption model of the laser-fluid coupled field. The theoretical background of this problem is introduced, the models are derived, argued mathematically and the results of these models are presented in this work.Different models that describe the radiation flux through a finite volume grid are presented and discussed. The models have been implemented in OpenFoam® and the results were visualized in Paraview.The source code of the multi-physical laser material processing simulation software was developed by IFT Vienna University of Technology and is their intellectual property.