Large eddy simulation of multiphase flows using the volume of fluid method: Part 2—A-posteriori analysis of liquid jet atomization

Abstract

Multiphase flows with two or more immiscible liquids, separated by a sharp interface with surface tension, occur in a large variety of environmental and industrial flow problems. The ability to accurately predict such flows has implications for safety, economy, and ecology. As a scale resolving technique, large eddy simulation (LES) is a turbulence model that has the potential to describe such flows with good accuracy. However, during the filtering process of the two-phase flow equations, several unclosed terms appear that are unknown from single-phase flow and their modelling is not yet standardized in the open literature. In this paper, the unknown terms are systematically analyzed based on a-posteriori LES and comparison with a direct numerical simulation (DNS) database. It is shown that the closures for each unknown term strongly interact with the other terms and as well with the numerical scheme. Therefore, only a modelling strategy consisting of a complete set of sub-models and numerical discretization can be identified, rather than individual optimal models. Several promising alternatives are identified and discussed, based on existing and newly developed turbulence and interfacial subgrid scale (SGS) closures.

Sub-grid Scale Modelling and a-Posteriori Tests with a Morphology Adaptive Multifield Two-Fluid Model Considering Rising Gas Bubbles

“…The Weber-number models We-KE-0.25 and We-Re reveal resulting model forces, which mainly appear at the lower side of the gas bubble acting in a direction, such that they counteract the curvature of the interface. In this way, the behaviour is reproduced, which was the theoretical starting point for formulating the Weber-number model (Ketterl et al 2019). At t = 2.8 both Weber-number models reveal similar model forces, whereas at t = 4.2 We-KE-0.25 shows a smaller effect compared to We-Re, especially in the region and the ends of the ligaments.…”

“…The influence of those terms has been assessed with a-priori investigations (Labourasse et al 2004(Labourasse et al , 2007Toutant et al 2006Toutant et al , 2008Toutant et al , 2009aVincent et al 2008;Larocque et al 2010;Chesnel et al 2011;Liovic and Lakehal 2007a;Klein 2016, 2018;Klein et al 2019;Mimouni et al 2017;Hasslberger et al 2020;Saeedipour et al 2019a;Saeedipour and Schneiderbauer 2019). In only a few investigations model formulations for those unclosed terms have been applied in actual multiphase simulations for a-posteriori model assessment Lakehal 2007a, b, 2012;Saeedipour et al 2019a, b;De Villiers et al 2004;Aniszewski et al 2012;Herrmann 2013Herrmann , 2015Ketterl et al 2019). All of the previously listed investigations have been carried out in the context of the one-fluid formulation.…”

A-Priori Assessment of Interfacial Sub-grid Scale Closures in the Two-Phase Flow LES Context

“…For all models based on the eddy viscosity concept (not only related to the closure of momentum advection), another interesting approach (Saeedipour and Schneiderbauer 2019) accounts for unresolved interfacial work done by surface tension by adding a correction term to increase the turbulent viscosity at the interface. Using the concept of a critical grid-based Weber number, Ketterl et al (2019) recently introduced a sub-grid model which increases the surface tension coefficient depending on the local flow conditions and the local curvature of the interface to ensure a solution that can be well represented by the grid.…”

An experimental study on drop formation from a capillary tube

“…Drop and/or jet emission from a capillary nozzle or an orifice plate is an important process that widely occurs in nature, industrial processes, and medical and food applications [1][2][3][4][5][6]. The forms of droplets and/or jets that are ejected from capillary tubes depend on the liquid flow rate, where the transition from a drop-by-drop regime to a continuous jet is an important topic.…”