Modeling heat transfer in dilute two-phase flows using the Mesoscopic Eulerian Formalism

In dilute two-phase flows, accurate prediction of the temperature of the dis- persed phase can be of paramount importance. Indeed, processes such as evaporation or chemical reactions are strongly non-linear functions of heat transfer between the carrier and dispersed phases. This study is devoted to the validation of an Eulerian description of the dispersed phase –the Meso- scopic Eulerian Formalism (MEF)– in the case of non-isothermal flows. Di- rect numerical simulations using the MEF are compared to a reference La- grangian simulation for a two-dimensional non-isothermal turbulent jet laden with solid particles. The objectives of this paper are (1) to study the influ- ence of the thermal inertia of particles on their temperature distribution and (2) conduct an a posteriori validation of the MEF, which was recently ex- tended to non-isothermal flows. The focus is on the influence of additional terms in the MEF governing equations, namely heat fluxes arising from the Random Uncorrelated Motion (RUM). Results show that mean and rms of particle temperature are strongly dependent of the thermal Stokes number. The mean temperature is satisfactorily predicted by the MEF, comparing to the Lagrangian reference. Under the conditions of the present study, the RUM heat fluxes have a marginal influence on the mean particle tempera- ture. However, a significant impact was observed on the magnitude of particle temperature fluctuations. Neglecting the RUM heat fluxes leads to erroneous results while the Lagrangian statistics are recovered when it is accounted for in the regimes of low to moderate thermal Stokes number

Multi-scale spray atomization model

International audienceThe purpose of the present article is to present a dynamic multi-scale approach for turbulent liquid jet atomization in dense flow (primary atomization), together with the possibility to recover Interface Capturing Method (ICM) / Direct Numerical Simulation (DNS) features for well resolved liquid-gas interface. A full ICM-DNS approach should give the best comparison with experimental data, but it is not industrially affordable for the time being, therefore models are mandatory. A numerical representation based on full ICM-DNS, for the initial destabilization of the complex turbulent liquid jet, going up to the spray formation, for which well established numerical models can be used, is appealing but has not yet been applied. Indeed such an approach requires the ICM-DNS to be applied up to the formation of each individual droplet. Hence, in many situation models have to be applied to the dense, unresolved and turbulent liquid-gas flow. To achieve this goal, the most important unresolved phenomena to address are, the sub-grid turbulent liquid flux and surface density, in which models based on the so-called Euler-Lagrange Spray Atomization (ELSA) concept, were developed and have been successfully applied to an Engine Combustion Network (ECN) database, in both RANS/LES (Reynolds-Averaged Navier-Stoke/Large Eddy Simulation) context. An innovative coupling between ICM and a complete ELSA approach was tested based on Interface Resolved Quality (IRQ) sensors to determine locally and dynamically whether or not the interface can be well captured. The ultimate aim is to conduct numerical simulations of fuel injection in an industrial scale, for which comprehensive database has been set up. The test case has been chosen for two reasons: (i) previous numerical studies showed, on the same test case, that RANS turbulence model requires a strong modification to get appropriate results, hence prompted the use of LES models. And (ii), liquid Reynolds and gas Weber numbers are relatively low, compared with ECN test cases, hence more flow regions are expected to be resolved. Results showed that using a fully resolved interface model in the whole domain, provides results in good agreement with the experiment in the primary atomization region only. Indeed, it effectively captured the surface instabilities and liquid structure detachments. In the far field, however, this model becomes rapidly unadapted downward in the dispersed spray region, and the ICM-ELSA model was able instead to treat low volume fractions of atomized liquid, where velocity fluctuations become important

Simulation DNS de l'interaction flamme-paroi dans les moteurs à allumage commandé

Dans le cadre du projet INTERMARC (INTERaction dans les Moteurs à Allumage Commandé), la tâche du CORIA a consisté à produire une base de données à l'échelle RANS (provenant de données DNS) afin de tester, valider et modifier le modèle d'interaction développée par IFPen. Ce modèle vise l'ajout d'une composante d'interaction, phénomène non pris en compte par les lois de paroi actuelles.Ce projet repose sur l'interaction forte entre les différents protagonistes présents. Le CORIA et le CETHIL ont travaillé ensemble à la réalisation d'une base de données pour tester les modèles initiaux proposés par IFPen, puis en fonction des résultats obtenus, à itérer avec IFPen pour modifier et améliorer les modèles. Ces tests ont inclus des simulations 2D laminaires, 2D turbulentes, et 3D turbulentes.Under the INTERMARC project (Flame wall interaction in spark ignition engines), CORIA's job was to produce a database to RANS scale (from DNS data) to test, validate and modify the interaction model developed by IFPEN. This model aims the addition of the interaction phenomena, non-captured by the current wall laws. This project is based on the strong interaction between the different actors. The CORIA and the CETHIL have worked together in the creation of the database, where the experimental data were also used to validate the resuslts of the DNS code.CORIA then used this database to test the original model proposed by IFPPEN, then according to the resuslts obtained, CORIA iterated with IFPEN to modify and improve the models. These tests included laminar 2D simulations, 2D turbulent and 3D turbulent simulations.ROUEN-INSA Madrillet (765752301) / SudocSudocFranceF

Simulation numérique directe des écoulements liquide-gaz avec évaporation (application à l'atomisation)

Le but de cette thèse est d'étudier numériquement les écoulements diphasiques liquide-gaz à l'aide d'une méthode de suivi d'interface précise. Tout d'abord, nous mettons en place une configuration turbulence homogène isotrope diphasique. Cette configuration est utilisée pour étudier la turbulence liquide-gaz ainsi que le modèle ELSA. A l'aide de la simulation présentée il a été possible de déterminer les constantes de modélisation et de valider les termes sources utilisés dans la zone dense du spray. Ensuite, le phénomène d'évaporation est étudié en utilisant dans un premier temps un scalaire passif puis en utilisant un formalisme DNS d'évaporation. Les équations d'énergie et des espèces ont été ajoutées dans le code ARCHER. La validation de la DNS d'évaporation a été réalisée en comparant nos résultats aux solutions théoriques, tel que la loi du D2. Les limitations et les apports de cette approche sont finalement discutés et des perspectives d'améliorations sont proposées.The aim of this thesis is to study numerically two phase flow using accurate interface tracking method. First, a two phase flow homogeneous isotropic turbulence is performed. This numerical configuration is used to study two phase flows turbulence and the ELSA model used in primary atomization modelling. Based on these results, modelling constants and source terms have been determined and validated. Then the evaporation process is studied and modelized by using a passive scalar and then by using a DNS formalism. Energy and species equations are added in the ARCHER code. Validation of the DNS performed by comparing the DNS results with theorical solution, such as the D2 law. Finally, limitations and interests of this approach are discussed and further improvements are proposed.ROUEN-INSA Madrillet (765752301) / SudocSudocFranceF

Liquid transport in scale space

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 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

Subgrid Liquid Flux and interface modelling for LES of Atomization

[EN] Traditional Discrete Particle Methods (DPM) such as the Euler-Lagrange approaches for modelling atomization, even if widely used in technical literature, are not suitable in the near injector region. Indeed, the first step of atomization process is to separate the continuous liquid phase in a set of individual liquid parcels, the so-called primary break-up. Describing two-phase flow by DPM is to define a carrier phase and a discrete phase, hence they cannot be used for primary breakup. On the other hand, full scale simulations (direct simulation of the dynamic DNS, and interface capturing method ICM) are powerful numerical tools to study atomization, however, computational costs limit their application to academic cases for understanding and complementing partial experimental data. In an industrial environment, models that are computationally cheap and still accurate enough are required to meet new challenges of fuel consumption and pollutant reduction. Application of DNS-ICM methods without fairly enough resolution to solve all length scales are currently used for industrial purpose. Nevertheless, effects of unresolved scales are generally cast aside. The Euler-Lagrange Spray Atomization model family (namely, ELSA, also call, Σ − �� or Ω − ��) developed by Vallet and Borghi pioneering work [1], and [2], at the contrary aims to model those unresolved terms. This approach is actually complementary to DNS-ICM method since the importance of the unresolved term depends directly on mesh resolution. For full interface resolution the unclosed terms are negligible, except in the far-field spray when the unresolved terms become dominant. Depending on the complexity of the flow and the available computational resources, a Large Eddy Simulation (LES) formalism could be employed as modelling approach. This work focus on the two main terms that drive these different modelling approaches namely the subgrid turbulent liquid flux and the resolved interface. Thanks to the open source library OpenFoam® this work is an attempt to review and to release an adapted modelling strategy depending on the available mesh resolution. For validation, these solvers are tested against realistic experimental data to see the overall effect of each model proposal.This work was partly supported European Union’s Horizon 2020 research and innovation program under the Sklodowska-Curie grant agreement No. 675676. Simulations were carried out at TGCC (The Curie supercomputer, owned by GENCI and operated into the TGCC by CEA), and at CRIHAN (Centre de Ressources de Haute Normandie).Anez, J.; Ahmed, A.; Puggelli, S.; Reveillon, J.; Brändle De Motta, JC.; Demoulin, F. (2017). Subgrid Liquid Flux and interface modelling for LES of Atomization. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 385-393. https://doi.org/10.4995/ILASS2017.2017.4694OCS38539

Where does the drop size distribution come from?

[EN] This study employs DNS of two-phase flows to enhance primary atomization understanding and modelling to be used 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 liquidgas 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 tools proposed to follow the formation of the spray with the pioneering work done on scale distribution analysis.Canu, R.; Dumouchel, C.; Duret, B.; Essadki, M.; Massot, M.; Ménard, T.; Puggelli, S.... (2017). Where does the drop size distribution come from?. En Ilass Europe. 28th european conference on Liquid Atomization and Spray Systems. Editorial Universitat Politècnica de València. 605-612. https://doi.org/10.4995/ILASS2017.2017.4706OCS60561

Internal Numerical Simulation of a Swirl Simplex Atomizer to Predict Atomization Outputs

International audienc

Numerical procedures to generate and to visualize flow fields from analytical or experimental statistics : turbulent velocity, fluctuating scalars and variable density sprays'

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