A robust incompressible Navier-Stokes solver for high density ratio multiphase flows

We study bubble break-up in homogeneous and isotropic turbulence by direct numerical simulations of the two-phase incompressible Navier–Stokes equations. We create the turbulence by forcing in physical space and introduce the bubble once a statistically stationary state is reached. We perform a large ensemble of simulations to investigate the effect of the Weber number (the ratio of turbulent and surface tension forces) on bubble break-up dynamics and statistics, including the child bubble size distribution, and discuss the numerical requirements to obtain results independent of grid size. We characterize the critical Weber number below which no break-up occurs and the associated Hinze scale , an order of magnitude smaller than the parent bubble. The separation of scales between the parent and child bubble is a signature of a production process non-local in scale. The formation mechanism of these sub-Hinze scale bubbles relates to rapid large deformation and successive break-ups: the first break-up in a sequence leaves highly deformed bubbles which will break again, without recovering a spherical shape and creating an array of much smaller bubbles. We discuss the application of this scenario to the production of sub-Hinze bubbles under breaking waves.

https://www.cambridge.org/core/services/aop-cambridge-core/content/view/7F8DADA87ABE117F5FE39183417D650B/S0022112021002433a.pdf/div-class-title-sub-hinze-scale-bubble-production-in-turbulent-bubble-break-up-div.pdf

Sub-Hinze scale bubble production in turbulent bubble break-up

https://hal.archives-ouvertes.fr/hal-03041062/document

A three-phase VOF solver for the simulation of in-nozzle cavitation effects on liquid atomization

https://hal.archives-ouvertes.fr/hal-02368869/document

A 3D Moment of Fluid method for simulating complex turbulent multiphase flows

When a liquid stream is injected into a gaseous atmosphere, it destabilizes and continuously passes through different states characterized by different morphologies. Throughout this process, the flow dynamics may be different depending on the region of the flow and the scales of the involved liquid structures. Exploring this multi-scale, multi-dimensional phenomenon requires some new theoretical tools, some of which need yet to be elaborated. Here, a new analytical framework is proposed on the basis of two-point statistical equations of the liquid volume fraction. This tool, which originates from single phase turbulence, allows us notably to decompose the fluxes of liquid in flow–position space and scale space. Direct numerical simulations of liquid–gas turbulence decaying in a triply periodic domain are then used to characterize the time and scale evolution of the liquid volume fraction. It is emphasized that two-point statistics of the liquid volume fraction depend explicitly on the geometrical properties of the liquid–gas interface and in particular its surface density. The stretch rate of the liquid–gas interface is further shown to be the equivalent for the liquid volume fraction (a non-diffusive scalar) of the scalar dissipation rate. Finally, a decomposition of the transport of liquid in scale space highlights that non-local interactions between non-adjacent scales play a significant role.

/pdf/liquid-transport-in-scale-space-jgvg27qxhb.pdf

Liquid transport in scale space

Where does the droplet size distribution come from

https://hal.archives-ouvertes.fr/hal-01827180/document

A pressure based method for vaporizing compressible two-phase flows with interface capturing approach

/pdf/curvature-based-interface-resolution-quality-irq-indicator-5fmotxurbq.pdf

Curvature-based interface resolution quality (irq) indicator to assess simulation accuracy

This study employs DNS of two-phase flows to enhance primary atomization understanding and modelling to beused in numerical simulation in RANS or LES framework. In particular, the work has been aimed at improving the information on the liquid-gas interface evolution available inside the Eulerian-Lagrangian Spray Atomization (ELSA) framework. Even though this approach has been successful to describe the complete liquid atomization process from the primary region to the dilute spray, major improvements are expected on the establishment of the drop size distribution (DSD). Indeed, the DSD is easily defined once the spray is formed, but its appearance and even the mathematical framework to describe its creation during the initial breakup of the continuous liquid phase in a set of individual liquid parcels is missing. This is the main aim of the present work to review proposals to achieve a continuous description of the DSD formation during the atomization process.The attention is here focused on the extraction from DNS data of the behaviour of geometrical variable of the liquid- gas interface, such as the mean and Gauss surface curvatures. A DNS database on curvature evolution has been generated. A Rayleigh-Plateau instability along a column of liquid is considered to analyse and to verify the capabilities of the code in correctly predicting the curvature distribution. A statistical analysis on the curvatures data, in terms of probability density function, was performed in order to determine the physical parameters that control the curvatures on this test case. Two different methods are presented to compute the curvature distribution and in addition, the probability to be at a given distance of the interface is studied. This approach finally links the new toolsproposed to follow the formation of the spray with the pioneering work done on scale distribution analysis. DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4706

Romain Canu

Papers

Where does the droplet size distribution come from

A pressure based method for vaporizing compressible two-phase flows with interface capturing approach

Curvature-based interface resolution quality (irq) indicator to assess simulation accuracy

Where does the drop size distribution come from