Littérature scientifique sur le sujet « Eulerian RANS »

An Eulerian/Lagrangian computational procedure was developed for the prediction of cavitation inception by event rate. The carrier-phase flow field was computed using an Eulerian Reynolds-averaged Navier-Stokes (RANS) solver. The Lagrangian analysis was one-way coupled to the RANS solution, since at inception, the contributions of mass, momentum, and energy of the microbubbles to the carrier flow are negligible. The trajectories were computed using Newton’s second law with models for various forces acting on the bubble. The growth was modeled using the Rayleigh-Plesset equation. The important effect of turbulence was included by adding a random velocity component to the mean flow velocity and by reducing the local static pressure. Simulation results for the Schiebe body indicate agreement with experimentally observed trends and a significant event rate at cavitation indices above visual inception.

This paper is addressing of a coupling Large-eddy simulation (LES) and RANS turbulence models with mixture fraction/probability density function as a combustion model. The two models have been implemented to simulate ethanol-air spray combustion. The gas phase is described with the Eulerian approach while the liquid phase is designed using a Lagrangian framework. The LES/PDF approach is obtained statistically. The sub-grid scale energy equation is used with the LES/PDF approach. The numerical results are validated with experimental data. Both LES/PDF and RANS/PDF approaches are compared with the experimental data. The LES/PDF approach shows a good agreement in predicting the average gas temperature compared with RANS/PDF approach. The LES/PDF shows a better prediction of both turbulence intensity profiles and the vortices which are generated in the turbulent flow in comparison with the RANS/PDF approach.

In the present study, an erosion analysis of an industrial pump’s casing and impeller blades has been performed computationally. Effects of various critical parameters, i.e., the concentration and size of solid particles, exit pressure head, and cavitation on the erosion rate density of the casing and blade have been investigated. Commercial codes CFX, ICEM-CFD, and ANSYS Turbogrid are employed to solve the model, mesh generation for the casing, and mesh generation of the impeller, respectively. The Eulerian-Eulerian method is employed to model the pump domain’s flow to solve the two phases (water and solid particles) and the interaction between the phases. Published experimental data was utilized to validate the employed computational model. Later, a parametric study was conducted to evaluate the effects of the parameters mentioned above on the erosion characteristics of the pump’s casing and impeller’s blade. The results show that the concentration of the solid particles significantly affects the pump’s erosion characteristics, followed by the particle size and distribution of the particle size. On the other hand, the exit pressure head and cavitation do not affect the erosion rates considerably but significantly influence the regions of high erosion rate densities.

A method to predict pitch and roll damping derivatives of aircraft geometries with fins using an unsteady RANS solver is presented. A three-dimensional structured RANS solver based on the arbitrary Lagrangian-Eulerian (ALE) formulation with a dynamically deforming mesh algorithm is used and validated with the wind tunnel and ballistic range data available in the literature. Roll and pitch damping derivatives are calculated from load history of the unsteady flow around the model. A standard research configuration, known as the Basic Finner, is studied under forced pitching and rolling conditions. Pitching and rolling motions with oscillation are analyzed at supersonic Mach numbers ranging from 1.5 to 2.5. Predicted results showed good agreement with the available wind tunnel data.

Numerical study and RANS simulations have been applied to investigate the incompressible free surface flow around the stern hull of Liquefied Natural Gas (LNG) ship affected by working propeller behind of her. Experimental works are carried out using LNG ship model in Marine Teknologi Center (MTC) of Univrsiti Teknologi Malaysia (UTM) to verify the computational fluid dynamic (CFD) results. Ansys-CFX 14.0 based on viscous flow finite volume code using the two-phase Eulerian–Eulerian fluid approach and shear stress transport (SST) turbulence model have been used in this study. A tetrahedral unstructured combined with prism grid were used with the viscous flow code for meshing the computational domain of water surface around it. CFD simulation has been verified using available experimental results. Finally, the flow structure, streamlines, velocity and pressure distribution around stern hull and propeller zone are discussed and analysed.

The Eulerian–Lagrangian–Agent method (ELAM) couples three modelling approaches into a single, integrated simulation environment: (i) Eulerian descriptions, (ii) Lagrangian formulations, and (iii) agent reference frameworks. ELAMS are particularly effective at decoding and simulating the motion dynamics of individual aquatic organisms, using the output of high fidelity computational fluid dynamics (CFD) models to represent complex flow fields. Here we describe the application of an ELAM to design a juvenile fish passage facility at Wanapum Dam on the Columbia River in the United States. This application is composed of three parts: (1) an agent-based model, that simulates the movement decisions made by individual fish, (2) an Eulerian CFD model that solves the 3D Reynolds-averaged Navier–Stokes (RANS) equations with a standard k–ɛ turbulence model with wall functions using a multi-block structured mesh, and (3) a Lagrangian particle-tracker used to interpolate information from the Eulerian mesh to point locations needed by the agent model and to track the trajectory of each virtual fish in three dimensions. We discuss aspects of the computational mesh topology and other CFD modeling topics important to this and future applications of the ELAM model for juvenille salmon, the Numerical Fish Surrogate. The good match between forecasted (virtual) and measured (observed) fish passage proportions demonstrates the value-added benefit of using agent-based models (i.e. the Numerical Fish Surrogate model) as part of common engineering practice for fish passage design and, more fundamentally, to simulate complex ecological processes.

This review covers the scope of multiscale computational fluid dynamics (CFD), laying the framework for studying hydrodynamics with and without chemical reactions in single and multiple phases regarded as continuum fluids. The molecular, coarse-grained particle, and meso-scale dynamics at the individual scale are excluded in this review. Scoping single-scale Eulerian CFD approaches, the necessity of multiscale CFD is highlighted. First, the Eulerian CFD theory, including the governing and turbulence equations, is described for single and multiple phases. The Reynolds-averaged Navier–Stokes (RANS)-based turbulence model such as the standard k-ε equation is briefly presented, which is commonly used for industrial flow conditions. Following the general CFD theories based on the first-principle laws, a multiscale CFD strategy interacting between micro- and macroscale domains is introduced. Next, the applications of single-scale CFD are presented for chemical and biological processes such as gas distributors, combustors, gas storage tanks, bioreactors, fuel cells, random- and structured-packing columns, gas-liquid bubble columns, and gas-solid and gas-liquid-solid fluidized beds. Several multiscale simulations coupled with Eulerian CFD are reported, focusing on the coupling strategy between two scales. Finally, challenges to multiscale CFD simulations are discussed. The need for experimental validation of CFD results is also presented to lay the groundwork for digital twins supported by CFD. This review culminates in conclusions and perspectives of multiscale CFD.

Combustion of pulverized biomass in a laboratory swirl burner is computationally investigated. The two-phase flow is modelled by an Eulerian-Lagrangian approach. The particle size distribution and turbulent particle dispersion are considered. The radiative heat transfer is modelled by the P1 method. For modelling turbulence, different RANS modelling approaches are applied. The pyrolysis of the solid fuel is modelled by a single step mechanism. For the combustion of the volatiles a two-step reaction mechanism is applied. The gas-phase conversion rate is modelled by the Eddy Dissipation Model, combined with kinetics control. The results are compared with measurements.

Vue la situation actuelle de ressources en combustibles fossiles menacées d’épuisement et des niveaux élevés d’émissions de polluants atmosphériques, l’état de l’art des recherches sur la combustion est confronté à deux défis principaux. Il s’agit d’une part d’optimiser l’efficacité de la combustion des combustibles fossiles et d’autre part du développer et d’appliquer des tratégies puissantes pour réduire la quantité de gaz polluants rejetésdans l’air tout en respectant les nouvelles normes d’émission conformément aux politiques énergétiques mondiales.Dans ce contexte, les technologies de captage et de stockage du dioxyde de carbone (CSC) jouent un rôle important en tant que stratégie énergétique adapteée en vue de l’atténuation des émissions de CO2 . L’un des aspects importants des techniques de CSC est l’oxydation du gaz naturel dans les conditions d’oxycombustion. Cependant, très peu de contributions scientifiques ont été consacrées à la recherche de ces systèmes de combustion, de sorte queles processus d’oxycombustion ne sont pas assez compris.L’objectif du présent travail est de développer et d’appliquer une méthode numérique avancée pour la simulation de l’oxycombustion. Cette approche a été intégrée dans la platforme numérique OpenFOAM et est capable de reproduire correctement l’interaction chimie-turbulence (ICT) pour les régimes de combustion non prémélangés. Le modèle proposé, qui est conçu pour les applications de RANS et LES, consiste en une fonction de densité de probabilité de transport (PDF) dans le contexte de la méthodologie du champ stochastique eulérien (ESF) combiné à un mécanisme de réduction chimique basé sur la variable d’avancement de la flamme (FPV). Dans le cadre la simulation des grandeséchelles (LES), la méthode proposée permet une description précise de l’influence des fluctuations de la structure fine (sous-maille) sur la structure de la flamme et sur les caractéristiques de la combustion, y compris l’intéraction turbulence-chimie associée.Le modèle de combustion développé a été d’abord vérifié, puis validé et appliqué à diverses configurations de combustion turbulente, non prémélangée et de complexité croissante. Le premier cas d’essai pour la validation de la méthode dans le contexte du RANS et du LES est la flamme Sandia D, qui consiste en flamme turbulente de méthane pilotée. Les flammes d’essai suivantes sont des flammes Sandia non prémélangées A & B, qui fonctionnent à diffèrents nombres de Reynolds et sont caractérisées par un enrichissement important de CO2 et de H2 dans les flux d’oxydant et du combustible, respectivement. Toutes les configurations de validation et d’application étudiés sont bien documentés avec des données expérimentales disponibles.Une comparaison entre les résultats des simulations obtenus et les données expérimentales concernant la température, les distributions scalaires, les PDFs et les diagrammes de dispersion montre un bon accord, en particulier dans le contexte de la LES. Enfin, ce travail démontre que l’approche hybride FSE/FPV peut éliminer les faiblesses associées à la méthode numérique β-PDF qui est basée sur l’approche FPV
In the prevailing situation of unsustainable fossil fuel resources and the elevated levels of air pollutant emissions, the state-of-the-art of combustion investigations confronts primarily two challenges. These are on the one hand the optimization of the fossil fuel combustion efficiency and on the other hand the development and the application of robust strategies to reduce the amount of the released pollutant gases with respect to the new emission standards in accordance with the global energy policies.Within this context, the carbon dioxide capture and storage (CCS) technologies play an important role as an accepted strategy towards the mitigation of CO 2 emissions. One of the important aspects of the CCS techniques is the oxidation of natural gas under oxy-fuel combustion conditions. However, very few scientific contributions have been devoted to the research of these systems, so that there is a lack of understanding of the oxy-combustion processes.The present work aims at the development and the application of an advanced numerical approach for the simulation of oxy-fuel combustion in which the TCI is adequatelyaccounted for within non-premixed combustion regimes using the OpenFOAM platform.The suggested model which is designed for both RANS and LES applications consists of a combination of a transported probability density function approach following the Eulerian Stochastic field methodology and the flamelet progress variable (FPV) chemistry reduction mechanism. In the LES framework, the proposed method accurately represents the effect of the sub-grid fluctuations on the flame structure and on combustion characteristics along with the interaction between turbulence and chemistry.The implemented developed combustion model is first verified, and then validated and applied to different turbulent non-premixed combustion configurations featuring an increasing order of complexity. In particular, Sandia flame D which consists of a turbulent piloted methane-air jet flame is first employed for model validation in both RANS and LES contexts. The next flames are more challenging cases, namely the non-premixed Sandia oxy-flame series (A & B), which are operated under different Re numbers and characterized by various CO 2 and H 2 enrichments in the oxidizer and fuel streams, respectively. All investigated cases are well documented with available experimentalmeasurements.The comparison of the obtained results with experimental data in terms of temperature, scalar distributions, PDFs and scatter plots agree satisfactorily, essentially in the LES context.This work finally reveals that the hybrid ESF/FPV approach removes the weaknesses of the presumed probability density function based FPV modeling (β-PDF)

[ES] El principal desafío en los motores turbina de gas empleados en aviación reside en aumentar la eficiencia del ciclo termodinámico manteniendo las emisiones contaminantes por debajo de las rigurosas restricciones. Ésto ha conllevado la necesidad de diseñar nuevas estrategias de inyección/combustión que operan en puntos de operación peligrosos por su cercanía al límite inferior de apagado de llama. En este contexto, el concepto Lean Direct Injection (LDI) ha emergido como una tecnología prometedora a la hora de reducir los óxidos de nitrógeno (NOx) emitidos por las plantas propulsoras de los aviones de nueva generación. En este contexto, la presente tesis tiene como objetivos contribuir al conocimiento de los mecanismos físicos que rigen el comportamiento de un quemador LDI y proporcionar herramientas de análisis para una profunda caracterización de las complejas estructuras de flujo de turbulento generadas en el interior de la cámara de combustión. Para ello, se ha desarrollado una metodología numérica basada en CFD capaz de modelar el flujo bifásico no reactivo en el interior de un quemador LDI académico mediante enfoques de turbulencia U-RANS y LES en un marco Euleriano-Lagrangiano. La resolución numérica de este problema multi-escala se aborda mediante la descripción completa del flujo a lo largo de todos los elementos que constituyen la maqueta experimental, incluyendo su paso por el swirler y entrada a la cámara de combustión. Ésto se lleva a cabo través de dos códigos CFD que involucran dos estrategias de mallado diferentes: una basada en algoritmos de generación y refinamiento automático de la malla (AMR) a través de CONVERGE y otra técnica de mallado estático más tradicional mediante OpenFOAM. Por un lado, se ha definido una metodología para obtener una estrategia de mallado óptima mediante el uso del AMR y se han explotado sus beneficios frente a los enfoques tradicionales de malla estática. De esta forma, se ha demostrado que la aplicabilidad de las herramientas de control de malla disponibles en CONVERGE como el refinamiento fijo (fixed embedding) y el AMR son una opción muy interesante para afrontar este tipo de problemas multi-escala. Los resultados destacan una optimización del uso de los recursos computacionales y una mayor precisión en las simulaciones realizadas con la metodología presentada. Por otro lado, el uso de herramientas CFD se ha combinado con la aplicación de técnicas de descomposición modal avanzadas (Proper Orthogonal Decomposition and Dynamic Mode Decomposition). La identificación numérica de los principales modos acústicos en la cámara de combustión ha demostrado el potencial de estas herramientas al permitir caracterizar las estructuras de flujo coherentes generadas como consecuencia de la rotura de los vórtices (VBB) y de los chorros fuertemente torbellinados presentes en el quemador LDI. Además, la implementación de estos procedimientos matemáticos ha permitido tanto recuperar información sobre las características de la dinámica de flujo como proporcionar un enfoque sistemático para identificar los principales mecanismos que sustentan las inestabilidades en la cámara de combustión. Finalmente, la metodología validada ha sido explotada a través de un Diseño de Experimentos (DoE) para cuantificar la influencia de los factores críticos de diseño en el flujo no reactivo. De esta manera, se ha evaluado la contribución individual de algunos parámetros funcionales (el número de palas del swirler, el ángulo de dichas palas, el ancho de la cámara de combustión y la posición axial del orificio del inyector) en los patrones del campo fluido, la distribución del tamaño de gotas del combustible líquido y la aparición de inestabilidades en la cámara de combustión a través de una matriz ortogonal L9 de Taguchi. Este estudio estadístico supone un punto de partida para posteriores estudios de inyección, atomización y combus
[CA] El principal desafiament als motors turbina de gas utilitzats a la aviació resideix en augmentar l'eficiència del cicle termodinàmic mantenint les emissions contaminants per davall de les rigoroses restriccions. Aquest fet comporta la necessitat de dissenyar noves estratègies d'injecció/combustió que radiquen en punts d'operació perillosos per la seva aproximació al límit inferior d'apagat de flama. En aquest context, el concepte Lean Direct Injection (LDI) sorgeix com a eina innovadora a l'hora de reduir els òxids de nitrogen (NOx) emesos per les plantes propulsores dels avions de nova generació. Sota aquest context, aquesta tesis té com a objectius contribuir al coneixement dels mecanismes físics que regeixen el comportament d'un cremador LDI i proporcionar ferramentes d'anàlisi per a una profunda caracterització de les complexes estructures de flux turbulent generades a l'interior de la càmera de combustió. Per tal de dur-ho a terme s'ha desenvolupat una metodología numèrica basada en CFD capaç de modelar el flux bifàsic no reactiu a l'interior d'un cremador LDI acadèmic mitjançant els enfocaments de turbulència U-RANS i LES en un marc Eulerià-Lagrangià. La resolució numèrica d'aquest problema multiescala s'aborda mitjançant la resolució completa del flux al llarg de tots els elements que constitueixen la maqueta experimental, incloent el seu pas pel swirler i l'entrada a la càmera de combustió. Açò es duu a terme a través de dos codis CFD que involucren estratègies de mallat diferents: una basada en la generación automàtica de la malla i en l'algoritme de refinament adaptatiu (AMR) amb CONVERGE i l'altra que es basa en una tècnica de mallat estàtic més tradicional amb OpenFOAM. D'una banda, s'ha definit una metodologia per tal d'obtindre una estrategia de mallat òptima mitjançant l'ús de l'AMR i s'han explotat els seus beneficis front als enfocaments tradicionals de malla estàtica. D'aquesta forma, s'ha demostrat que l'aplicabilitat de les ferramente de control de malla disponibles en CONVERGE com el refinament fixe (fixed embedding) i l'AMR són una opció molt interessant per tal d'afrontar aquest tipus de problemes multiescala. Els resultats destaquen una optimització de l'ús dels recursos computacionals i una major precisió en les simulacions realitzades amb la metodologia presentada. D'altra banda, l'ús d'eines CFD s'ha combinat amb l'aplicació de tècniques de descomposició modal avançades (Proper Orthogonal Decomposition and Dynamic Mode Decomposition). La identificació numèrica dels principals modes acústics a la càmera de combustió ha demostrat el potencial d'aquestes ferramentes al permetre caracteritzar les estructures de flux coherents generades com a conseqüència del trencament dels vòrtex (VBB) i dels raigs fortament arremolinats presents al cremador LDI. A més, la implantació d'estos procediments matemàtics ha permès recuperar informació sobre les característiques de la dinàmica del flux i proporcionar un enfocament sistemàtic per tal d'identificar els principals mecanismes que sustenten les inestabilitats a la càmera de combustió. Finalment, la metodologia validada ha sigut explotada a traves d'un Diseny d'Experiments (DoE) per tal de quantificar la influència dels factors crítics de disseny en el flux no reactiu. D'aquesta manera, s'ha avaluat la contribución individual d'alguns paràmetres funcionals (el nombre de pales del swirler, l'angle de les pales, l'amplada de la càmera de combustió i la posició axial de l'orifici de l'injector) en els patrons del camp fluid, la distribució de la mida de gotes del combustible líquid i l'aparició d'inestabilitats en la càmera de combustió mitjançant una matriu ortogonal L9 de Taguchi. Aquest estudi estadístic és un bon punt de partida per a futurs estudis de injecció, atomització i combustió en cremadors LDI.
[EN] Aeronautical gas turbine engines present the main challenge of increasing the efficiency of the cycle while keeping the pollutant emissions below stringent restrictions. This has led to the design of new injection-combustion strategies working on more risky and problematic operating points such as those close to the lean extinction limit. In this context, the Lean Direct Injection (LDI) concept has emerged as a promising technology to reduce oxides of nitrogen (NOx) for next-generation aircraft power plants In this context, this thesis aims at contributing to the knowledge of the governing physical mechanisms within an LDI burner and to provide analysis tools for a deep characterisation of such complex flows. In order to do so, a numerical CFD methodology capable of reliably modelling the 2-phase nonreacting flow in an academic LDI burner has been developed in an Eulerian-Lagrangian framework, using the U-RANS and LES turbulence approaches. The LDI combustor taken as a reference to carry out the investigation is the laboratory-scale swirled-stabilised CORIA Spray Burner. The multi-scale problem is addressed by solving the complete inlet flow path through the swirl vanes and the combustor through two different CFD codes involving two different meshing strategies: an automatic mesh generation with adaptive mesh refinement (AMR) algorithm through CONVERGE and a more traditional static meshing technique in OpenFOAM. On the one hand, a methodology to obtain an optimal mesh strategy using AMR has been defined, and its benefits against traditional fixed mesh approaches have been exploited. In this way, the applicability of grid control tools available in CONVERGE such as fixed embedding and AMR has been demonstrated to be an interesting option to face this type of multi-scale problem. The results highlight an optimisation of the use of the computational resources and better accuracy in the simulations carried out with the presented methodology. On the other hand, the use of CFD tools has been combined with the application of systematic advanced modal decomposition techniques (i.e., Proper Orthogonal Decomposition and Dynamic Mode Decomposition). The numerical identification of the main acoustic modes in the chamber have proved their potential when studying the characteristics of the most powerful coherent flow structures of strongly swirled jets in a LDI burner undergoing vortex breakdown (VBB). Besides, the implementation of these mathematical procedures has allowed both retrieving information about the flow dynamics features and providing a systematic approach to identify the main mechanisms that sustain instabilities in the combustor. Last, this analysis has also allowed identifying some key features of swirl spray systems such as the complex pulsating, intermittent and cyclical spatial patterns related to the Precessing Vortex Core (PVC). Finally, the validated methodology is exploited through a Design of Experiments (DoE) to quantify the influence of critical design factors on the non-reacting flow. In this way, the individual contribution of some functional parameters (namely the number of swirler vanes, the swirler vane angle, the combustion chamber width and the axial position of the nozzle tip) into both the flow field pattern, the spray size distribution and the occurrence of instabilities in the combustion chamber are evaluated throughout a Taguchi's orthogonal array L9. Such a statistical study has supposed a good starting point for subsequent studies of injection, atomisation and combustion on LDI burners.
Belmar Gil, M. (2020). Computational study on the non-reacting flow in Lean Direct Injection gas turbine combustors through Eulerian-Lagrangian Large-Eddy Simulations [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/159882
TESIS

In the present study, a novel implicit numerical model to describe evaporation phenomena in the dense spray region is proposed. The main aim is to go beyond the limits of standard vaporization models, which are normally based on a dilute spray assumption, to deal with high liquid volume fractions. The proposed method is based on an a priori computation of steady state equilibrium conditions reached by a system composed by liquid, vapour and air at constant pressure combined with a modelled characteristic time of evaporation. Such equilibrium composition and temperature is then used inside numerical calculations to compute evaporation source terms. The new for-mulation allows to simulate evaporation process in the dense zone of the spray, where, due to the extremely low thermal relaxation time, classical explicit method can lead to unphysical results. Such innovative approach has been implemented in a multiphase solver in the framework of the CFD suite OpenFOAM. An Eulerian-Eulerian solver, de-rived from the Eulerian Lagrangian Spray Atomization (ELSA) model, has been used, in order to correctly describe the liquid-gas flow without assumptions on the topology of the liquid phase. Evaporation source terms have been modelled as function of the amount of surface available for mass and heat transfer. An analysis of the solver has been carried out in RANS framework in order to highlight the capabilities of the approach in dealing with high liquid volume fraction regions with a physically consistent representation of evaporation phenomena.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4652

This paper simulates the dispersed bubbly flow in a vertical tube with two different turbulence models based on Eulerian two-fluid frameworks. Both the RANS (Reynolds Averaged N-S equation) approach and LES (Large Eddy Simulation) approach can get results agreed with experiment well. The “wall peak” bubble distribution is captured. Compare with RANS with SST (Shear Stress Transport) turbulence model, the LES with WALE (Wall-Adapted Local Eddy-viscosity) sub-grid model can give transient and detail information of the flow field, and it shows better agreement.

Flash boiling is the rapid phase change of a pressurised fluid that emerges in ambient conditions below its vapourpressure. Flashing can occur either inside or outside the nozzle depending on the local pressure and geometry and the bubble formation leads to interfacial interactions that eventually influence the emerging spray. Lagrangian methods which exist in literature to simulate the flash atomisation and inter-phase heat transfer employ many sim- plifying assumptions. Typically, sub-models used for the break-up, collisions and evaporation introduce an extensive empiricism that might result in unrealistic predictions for cases like flashing. In this study, a fully Eulerian approach is selected employing the Σ − Y model proposed by Vallet and Borghi. The model tracks liquid structures of any shape and computes the spray characteristics comprising a modified version for the transport equation of the sur- face density. The main goal of this study is to investigate the performance of this model in flash boiling liquids using the Homogeneous Relaxation Model (HRM) developed by Downar-Zapolski, a model capable of capturing the heat transfer under sudden depressurisation conditions accounting for the non-equilibrium vapour generation. The model in this present study considers that the instantaneous quality would relax to the equilibrium value over a given timescale which is calculated using the flow field values. A segregated approach linking the HRM and Σ − Y is implemented in a compressible formulation in an attempt to quantify the effects of flash boiling in the spray dynamics. The developed model is naturally implemented in RANS in a dedicated solver HRMSonicELSAFoam. Results from simulations of two-phase jets of different subcooled fluids through sharp-edged orifices show that the proposed approach can accurately simulate the primary atomisation and give reliable predictions for the droplet sizes and distribution. Strong effects of the flashing and turbulent mixing on the jet are demonstrated. The model istested for turbulent flows within small nozzles and was developed within the open source code OpenFOAM.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.4667

In simulating fluid/solid-particle multiphase -flows, various methods are available. One approach is the combined Euler-Lagrange method, which simulates the fluid phase flow in the Eulerian framework and the discrete phase (particle) motion in the Lagrangian framework simultaneously. The Lagrangian approach, where particle motion is determined by the current state of the fluid phase flow, is also called the discrete phase model (DPM), in the context of numerical flow simulation. In this method, the influence of the particle motions on the fluid flow can be included (two-way interactions) but are more commonly excluded (one-way interactions, when the discrete phase concentration is dilute. The other approach is to treat the particle number concentration as a continuous species, a necessarily passive quantity determined by the fluid flow, with no influences from the particles on the fluid flow (one-way interactions only), except to the extent the discrete phase “continuum” alters the overall fluid properties, such as density. In this paper, we compare these two methods with experimental data for an indoor environmental chamber. The effects of injection particle numbers and the related boundary conditions are investigated. In the Euler-Lagrange interaction or DPM model for incompressible flow, the Eulerian continuous phase is governed by the Reynolds-averaged N-S (RANS) equations. The motions of particles are governed by Newton’s second law. The effects of particle motions are communicated to the continuous phase through a force term in the RANS equations. The second formulation is a pure Eulerian type, where only the particle-number concentration is addressed, rather than the motion of each individual particle. The fluid flow is governed by the same RANS equations without the particle force term. The particle-number concentration is simulated by a species transport equation. Comparisons among the models and with experimental and literature data are presented. Particularly, results with different numbers of released particles in the DPM will be investigated.

The objective of this study is to examine the impact of single and multi-component surrogate fuel mixtures on the atomization and mixing characteristics of non-reacting isothermal diesel engine sprays. An Eulerian modeling approach was adopted to simulate both the internal nozzle flow dynamics and the emerging turbulent spray in the near nozzle region in a fully-coupled manner. The Volume of Fluids (VoF) methodology was utilized to treat the two-phase flow dynamics including a Homogenous Relaxation approach to account for nozzle cavitation effects. To enable accurate simulations, the nozzle geometry and in-situ multi-dimensional needle lift and off-axis motion profiles have been characterized via the X-ray phase-contrast technique at Argonne National Laboratory. The flow turbulence is treated via the classical k–ϵ Reynolds Average Navier Stoke (RANS) model with in-nozzle and near field resolution of 30 μm. Several multi-component surrogate mixtures were implemented using linear blending rules to examine the behavior of petroleum, and alternative fuels including: JP-8, JP-5, Hydro-treated Renewable Jet (HRJ), Iso-Paraffinic Kerosene (IPK) with comparison to single-component n-dodecane fuel on ECN Spray A nozzle spray dynamics. The results were validated using transient rate-of-injection measurements from the Army Research Laboratory at Spray A conditions as well as projected density fields obtained from the line-of-sight measurements from X-ray radiography measurements at The Advanced Photon Source at Argonne National Laboratory. The conditions correspond to injection pressure, nominal fuel temperature, and ambient density of 1500 bar, 363 K, and 22.8 kg/m3, respectively. The simulation results provide a unique high-fidelity contribution to the effects of fuels on the spray mixing dynamics. The results can lead to improvements in fuel mixture distributions enhancing performance of military vehicles.

The present study shows the effects of Stokes number on the modeling of collisional interfacial area productionterms within the Σ-Y model. This model can be employed for CFD simulations of high Weber and Reynolds number sprays using a RANS turbulence modeling. Within the model production of interfacial area is assumed to result from turbulent stretching and turbulent droplet collisions. The modeling of collisional processes requires the calculation of a characteristic turbulent collision velocity. In the present work this velocity was determined under consideration of Stokes number effects leading to turbulent droplet velocity fluctuations attenuated with respect to the gas phase fluctuations and including partial correlation between the velocities. The influence of this new modeling approach is tested within a 2D spray simulation by comparing the Sauter mean diameters observed to the ones obtained by employing the modeling approaches proposed in the literature which do not consider any Stokes number effects.The reduced collision velocites in the new modeling lead to higher values for Sauter mean diameters in the spray.DOI: http://dx.doi.org/10.4995/ILASS2017.2017.5041

Flexibly supported two-degrees of freedom (2-DOF) airfoil in two-dimensional (2D) incompressible viscous turbulent flow subjected to a gust (sudden change of flow conditions) is considered. The structure vibration is described by two nonlinear ordinary differential equations of motion for large vibration amplitudes. The flow is modeled by Reynolds averaged Navier-Stokes equations (RANS) and by k–ω turbulence model. The numerical simulation consists of the finite element (FE) solution of the RANS equations and the equations for the turbulent viscosity. This is coupled with the equations of motion for the airfoil by a strong coupling procedure. The time dependent computational domain and a moving grid are taken into account with the aid of the arbitrary Lagrangian-Eulerian formulation. In order to avoid spurious numerical oscillations, the SUPG and div-div stabilizations are applied. The solution of the ordinary differential equations is carried out by the Runge-Kutta method. The resulting nonlinear discrete algebraic systems are solved by the Oseen iterative process. The aeroelastic response to a sudden gust is numerically analyzed with the aid of the developed FE code. The gust responses exhibit similar oscillations as those found in literature.

The first part of this work presents a comparison of predictions obtained with several two-equation type RANS turbulence models commonly used in industry against experimental data obtained by Whitelaw et al [1]. All examined models yield a relatively poor match in the flow region very close to the wall; agreement with the measurements improves significantly when moving further away from the wall. This concerns both the internal normal stress profiles and the average velocity profiles, the latter show improved prediction of the recirculation zone area when moving further into the main stream. Downstream behaviour for both models shows an excellent match more than 6 diameters away from the jet inlet, defined as the region after which the flow essentially resumes its normal duct behaviour[1]. Expanding upon these RANS results, another series of simulations using LES modelling with the standard Smagorinsky SGS model was conducted using the same grid and compared to the RANS-based results. Although performance in the most complex flow areas was slightly improved over RANS, this was at the cost of an increase of computation time by almost a factor of 6. The next stage involved developing a code based on the model for two-phase flow described in [2] to predict the atomisation pattern for a non-vaporising (or “cold”) flow based on the parameters of the previous simulations. This model implements transport equations for the liquid mass fraction and the average surface area per unit mass along with an equation for average density; resulting in an entirely Eulerian model which can be used to predict atomisation from first principles. Current work consists in development of additional source terms describing vaporisation in a strongly turbulent environment and further coupling with a combustion model applicable to the combustion chamber of an industrial gas turbine.

Abstract Submerged impingement jets are widely used in erosion/corrosion investigation as it is easy to control standoff distance as well as jet angle and flow velocities in experiments. In addition to experiments, typically Computational Fluid Dynamics (CFD) technique has been used to simulate slurry flow in this geometry to investigate erosion process and develop and verify erosion equations. This is done by solving Reynolds Averaged Navier-Stokes (RANS) equations with turbulence models, time-averaged fluid flow is revealed, and thus time-averaged erosion rate can be obtained by tracking particles in the fluid flow field. The current work shows that this seemingly simple flow displays unsteady flow structures in the stagnation zone of the flow field and its effects on erosion process was unclear. In this study, Large Eddy Simulation (LES) is used to simulate unsteady fluid flow in different impingement jets in Eulerian scheme. Then particles are injected randomly in the surface and tracked transiently to simulate unsteady erosion process in Lagrangian scheme. Finally, an erosion equation is used to calculate solid particle erosion rates. The LES Eulerian-Lagrangian erosion modeling are further validated by experimental fluid velocities and erosion profile measured before. It was found the accuracy of erosion prediction of small particles can be improved and unsteady properties can be well resolved by using this method.

It is well known that slamming and whipping can significantly contribute to a ship’s structural loading which can severely impact a ship’s operational safety. Therefore, a method of predicting severe transient structural loads is needed, especially for the design of future high-speed patrol boats and high-speed ferries. A number of computational fluid dynamics (CFD) codes have demonstrated the ability to cope with complex body shapes and to numerically capture the nonlinear effect of hydro-elasticity. However, validation is scarce both due to a lack of experimental data and the computational intensity of the problem. This paper describes a validation study of a Reynolds averaged Navier-Stokes (RANS) code (STAR-CCM+) and a Lagrangian-Eulerian fluid structure interaction (FSI) code (DYSMAS) using 10 degree wedge drop test experimental data obtained at the Naval Warfare Center, Carderock Division, December 2010.