Abstract
This paper presents a numerical model that intends to simulate efficiently the surface instability that arise in multiphase flows, typically liquid-gas, both for laminar or turbulent regimes. The model is developed on the in-house computing platform TermoFluids, and operates the finite-volume, direct numerical simulation (DNS) of multiphase flows by means of a conservative level-set method for the interface-capturing. The mesh size is optimized by means of an adaptive mesh refinement (AMR) strategy, that allows the dynamic re-concentration of the mesh in the vicinity of the interfaces between fluids, in order to correctly represent the diverse structures (as ligaments and droplets) that may rise from unstable phenomena. In addition, special attention is given to the discretization of the various terms of the momentum equations, to ensure stability of the flow and correct representation of turbulent vortices. As shown, the method is capable of truthfully simulate the interface phenomena as the Kelvin-Helmholtz instability and the Plateau-Rayleigh instability, both in the case of 2-D and 3-D configurations. Therefore it is suitable for the simulation of complex phenomena such as simulation of air-blast atomization, with several important application in the field of automotive and aerospace engines. A prove is given by our preliminary study of the 3-D coaxial liquid-gas jet.
Highlights
The study of the liquid atomization process is currently a problem not totally understood in the engineering field, due to the high complexity of the phenomena that lead to the generation and amplification of instabilities at the interface —an introduction to the involved physical processes is available in [1]
Several numerical methods have been proposed, spacing between the three main classes of computational fluid dynamics (CFD) models: in Reynolds-averaged Navier-Stokes equations (RANS) [2], the approach is based on a homogeneous formulation of the two-phase medium, and the transport of mean interface density is modeled by diffusion-like hypothesis, neglecting the effect of the interaction between liquid structures [3]; on the other side, large eddy simulations (LES) approaches [4] still suffer the complexity of coupling turbulence modeling and interface-capturing methods
Conclusions and future work In this paper we have demonstrated the ability of our numerical model to effectively represent some superficial phenomena in multiphase flows
Summary
The study of the liquid atomization process is currently a problem not totally understood in the engineering field, due to the high complexity of the phenomena that lead to the generation and amplification of instabilities at the interface —an introduction to the involved physical processes is available in [1]. That include the correct representation of surface phenomena, such as the growth of waves and filaments, as well as the generation of drops of varying size in primary and secondary atomization processes. The development of various numerical techniques in our computing platform allowed to study the phenomena responsible for the early surface instabilities, as well as the evolution of secondary structures, as droplets and ligaments, that rise from the destabilized liquids. Our simulations were carried out on both 2-D and 3-D configurations of liquid jets interacting with high speed air fluxes
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