Towards a Direct Numerical Simulation of Primary Jet Breakup with Evaporation

Abstract

The primary breakup of liquid jets plays an important role in fuel injection for combustion engines and gas turbines. Due to the ambient conditions the liquid also evaporates during breakup. Direct Numerical Simulations (DNS) are well suited for the analysis of this phenomena. As a first step towards an understanding of this problem, a DNS of an evaporating jet is carried out and a comparison with a non evaporating jet is presented. We use the in-house 3D Computational Fluid Dynamics (CFD) code Free Surface 3D (FS3D) to solve the incompressible Navier-Stokes equations. The Volume of Fluid (VOF) method is used in combinations with Piecewise Linear Interface Calculation (PLIC) to reconstruct a sharp interface. The energy equation is solved to obtain the phase change at the interface. We were able to conduct a purely Eulerian simulation of an evaporating jet during atomization. The morphology of the liquid jets and the vapour concentration are shown and analysed. The droplet size distribution shows the influence of evaporation, leading to smaller droplets. The presented results are in good accordance with our expectation as well as with other investigations in the literature. In addition, we present the results of an investigation into replacing pointers to fields in our code with arrays to improve computational performance. With this change we are able to increase the efficiency of the code and obtain a speed up of more than 40%.