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ISBN 9783843950848

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978-3-8439-5084-8, Reihe Thermodynamik

Jonathan Reutzsch
Direct Numerical Simulations of Phase Change Processes Using a Volume-of-Fluid Approach

183 Seiten, Dissertation Universität Stuttgart (2022), Softcover, A5

Zusammenfassung / Abstract

The goal of the present work is to contribute to the common research field of numerical methods for Direct Numerical Simulation of multiphase flows with phase change. The main focus is set on evaporation processes of droplets and the development of a new evaporation model. All methods are integrated into the software Free Surface 3D (FS3D) which comprises a numerical solver for the incompressible Navier-Stokes equations as well as the energy equation for multiphase flows within a Finite Volume formulation. The Volume-of-Fluid method is used to capture the different phases and the surface is reconstructed applying the PLIC algorithm.

The new framework contains a precise advection of the fluid and the gaseous phase. Two methods to describe at first the volume source in a consistent way and subsequently the velocities of all involved phases are presented. The physics of the phase change process is modeled by means of a fully consistent evaporation loop. It is shown that this approach is suitable to investigate various phenomena comprising multiphase flows with evaporation. A broad range of conditions from supercooled evaporating droplets to extreme ambiances at high temperatures and pressures leading to large evaporation rates can be simulated. Furthermore, it is possible to perform precise 3D simulations with complex interface structures at high velocities as well as setups containing a complete quiescent atmosphere without any significant interface deformation.

In order to investigate the potential and the physical accuracy of the model a multistage validation procedure is applied.

Several results are presented which show the high flexibility and correct predictability of the new evaporation model. Among them are simulations of supercooled droplets at different temperatures and varying humidity, oscillating droplets, an evaporating jet breakup, and a free falling droplet in an extreme ambiance.