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1
Farrell, Kevin J. « Eulerian/Lagrangian Analysis for the Prediction of Cavitation Inception ». Journal of Fluids Engineering 125, no 1 (1 janvier 2003) : 46–52. http://dx.doi.org/10.1115/1.1522411.
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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.
2
Zhu, Shanglong, Dirk Roekaerts, Artur Pozarlik et Theo van der Meer. « Eulerian–Lagrangian RANS Model Simulations of the NIST Turbulent Methanol Spray Flame ». Combustion Science and Technology 187, no 7 (26 février 2015) : 1110–38. http://dx.doi.org/10.1080/00102202.2015.1019616.
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Haran, Duaa Yaseen, et Ahmed Abed AL-Kadhem Majhool. « Application of LES/PDF and RANS/PDF approaches for simulation of spray combustion ». Al-Qadisiyah Journal for Engineering Sciences 14, no 2 (13 juillet 2021) : 109–16. http://dx.doi.org/10.30772/qjes.v14i2.752.
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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.
4
Alawadhi, Khaled, Bashar Alzuwayer, Mosab Alrahmani et Ahmed Murad. « Evaluation of the Erosion Characteristics for a Marine Pump Using 3D RANS Simulations ». Applied Sciences 11, no 16 (10 août 2021) : 7364. http://dx.doi.org/10.3390/app11167364.
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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.
5
Zhao, Zhong Liang, Hong Biao Wang, Yang Tao et Yuan Jing Wang. « Predictions of Dynamic Damping Coefficients of Basic Finner Based on CFD ». Applied Mechanics and Materials 380-384 (août 2013) : 215–18. http://dx.doi.org/10.4028/www.scientific.net/amm.380-384.215.
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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.
6
Nakisa, Mehdi, Adi Maimun Abdul Malik, Yasser M. Ahmed, Sverre Steen, Fatemeh Behrouzi, Reza Hassanzadeh et Ahmad F. Sabki. « Propeller Effect on 3D Flow at the Stern Hull of a LNG Carrier Using Finite Volume Method ». Applied Mechanics and Materials 554 (juin 2014) : 566–70. http://dx.doi.org/10.4028/www.scientific.net/amm.554.566.
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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.
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Weber, L. J., R. A. Goodwin, S. Li, J. M. Nestler et J. J. Anderson. « Application of an Eulerian–Lagrangian–Agent method (ELAM) to rank alternative designs of a juvenile fish passage facility ». Journal of Hydroinformatics 8, no 4 (1 décembre 2006) : 271–95. http://dx.doi.org/10.2166/hydro.2006.006.
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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.
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Ngo, Son Ich, et Young-Il Lim. « Multiscale Eulerian CFD of Chemical Processes : A Review ». ChemEngineering 4, no 2 (31 mars 2020) : 23. http://dx.doi.org/10.3390/chemengineering4020023.
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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.
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Larbi, Ahmed Amine, Abdelhamid Bounif, Mohamed Senouci, Iskender Gökalp et Mohamed Bouzit. « RANS modelling of a lifted hydrogen flame using eulerian/lagrangian approaches with transported PDF method ». Energy 164 (décembre 2018) : 1242–56. http://dx.doi.org/10.1016/j.energy.2018.08.073.
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Deniz Canal, Cansu, Erhan Böke et Ali Cemal Benim. « Numerical analysis of pulverized biomass combustion ». E3S Web of Conferences 321 (2021) : 01001. http://dx.doi.org/10.1051/e3sconf/202132101001.
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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.
11
Ku, Garam, Cheolung Cheong, Hanshin Seol et Hongseok Jeong. « Numerical investigation into effects of gas concentration and bubble collapse on tip vortex cavitation noise of NACA16-020 wing ». INTER-NOISE and NOISE-CON Congress and Conference Proceedings 263, no 5 (1 août 2021) : 1813–17. http://dx.doi.org/10.3397/in-2021-1958.
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In this study, the effects of gas concentration and bubble collapse on tip vortex cavitation noise of NACA16-020 wings are investigated using coupled Eulerian-Lagrangian method based on sequential application of Reynolds averaged Navier-Stokes (RANS) solver, bubble dynamics model and acoustic analogy. The bubble dynamics model used in the preceding study (Ku et al., 2020) is modified by including the gas pressure terms and the bubble collapse model, which depends on the timing and threshold of bubble collapse, the number, initial radius and location of divided bubbles. The validity of the modified bubble dynamics model is confirmed through its application to a benchmark problem where single bubble is triggered by laser. Then, the coupled Eulerian-Lagrangian method based on the modified bubble dynamic model is applied for the prediction of tip-vortex cavitation noise of NACA16-020 wing. The predicted results of the tip vortex pattern and acoustic pressure spectrum are compared with the measured results, which shows closer agreements between two results than those in the previous study.
12
Elfverson, Daniel, et Christian Lejon. « Use and Scalability of OpenFOAM for Wind Fields and Pollution Dispersion with Building- and Ground-Resolving Topography ». Atmosphere 12, no 9 (31 août 2021) : 1124. http://dx.doi.org/10.3390/atmos12091124.
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Complex flow and pollutant dispersion simulations in real urban settings were investigated by using computational fluid dynamics (CFD) simulations with the SST k−ω Reynolds-averaged Navier–Stokes (RANS) equation with OpenFOAM. The model was validated with a wind-tunnel experiment using two surface-mounted cubes in tandem, and the flow features were reproduced with the correct qualitative behaviour. The real urban geometry of the Parade Square in Warsaw, Poland was represented with both laser-scanning data for the ground geometry and the CityGML standard to describe the buildings as an example. The Eulerian dispersion of a passive scalar and the flow behaviour could be resolved within minutes over a computational domain with a size of 958 × 758 m2 and a height of 300 m with over 2 M cells due to the good and strong parallel scalability in OpenFOAM. This implies that RANS modelling with parallel computing in OpenFOAM can potentially be used as a tool for situational awareness on a local urban scale; however, entire cities would be too large.
13
Ku, Garam, Cheolung Cheong, Ilryong Park et Hanshin Seol. « Numerical Investigation of Tip Vortex Cavitation Inception and Noise of Underwater Propellers of Submarine Using Sequential Eulerian–Lagrangian Approaches ». Applied Sciences 10, no 23 (5 décembre 2020) : 8721. http://dx.doi.org/10.3390/app10238721.
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In this study, the high-fidelity numerical methods are developed to investigate the tip vortex cavitation (TVC) inception and noise of underwater propellers, namely, Model-A and Model-B, which are designed to investigate the effects of sweep angle on cavitation inception and noise. In addition, the entire body of the DARPA Suboff submarine is included to consider the effects of the inflow distortion originating from the boundary layer flow of the submarine body on the cavitating flow of the propellers. The Eulerian approach consisting of Reynolds-averaged Navier–Stokes (RANS) solver and the vortex model is coupled with the Lagrangian approach using the bubble dynamics equations and the acoustic analogy for nuclei initially distributed in inlet flow. First, three-dimensional incompressible unsteady RANS simulations are performed to predict the hydrodynamic flow field driven by underwater propellers installed on a DARPA Suboff submarine body. The Scully vortex model and dissipation vortex model (DVM) are used to regenerate the tip vortex dissipated by artificial numerical damping and low grid resolution around the vortex core center, which is identified by using minimum λ2-criterion in the swirling flow field originating from the propeller blade tip. Then, tip vortex cavitation inception is simulated by applying the bubble dynamics equations to nuclei initially distributed in the inflow region. The volume and location of each nucleus are obtained by solving the bubble dynamics equations on the flow field obtained using the Eulerian method. Finally, the cavitation noise is predicted by modeling each bubble with a point monopole source whose strength is proportional to its volume acceleration. The validity of the present numerical methods is confirmed by comparing the predicted acoustic pressure spectrum with the measured ones.
14
Lin, Chao, Ryozo Ooka, Hideki Kikumoto et Hongyuan Jia. « Eulerian RANS simulations of near-field pollutant dispersion around buildings using concentration diffusivity limiter with travel time ». Building and Environment 202 (septembre 2021) : 108047. http://dx.doi.org/10.1016/j.buildenv.2021.108047.
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Han, Han, Zifei Yin, Yijun Ning et Hong Liu. « Development of a 3D Eulerian/Lagrangian Aircraft Icing Simulation Solver Based on OpenFOAM ». Entropy 24, no 10 (27 septembre 2022) : 1365. http://dx.doi.org/10.3390/e24101365.
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A 3D icing simulation code is developed in the open-source CFD toolbox OpenFOAM. A hybrid Cartesian/body-fitted meshing method is used to generate high-quality meshes around complex ice shapes. Steady-state 3D Reynolds-averaged Navier-Stokes (RANS) equations are solved to provide the ensemble-averaged flow around the airfoil. Considering the multi-scale nature of droplet size distribution, and more importantly, to represent the less uniform nature of the Super-cooled Large Droplets (SLD), two droplet tracking methods are realized: the Eulerian method is used to track the small-size droplets (below 50 μm) for the sake of efficiency; the Lagrangian method with random sampling is used to track the large droplets (above 50 μm); the heat transfer of the surface overflow is solved on a virtual surface mesh; the ice accumulation is estimated via the Myers model; finally, the final ice shape is predicted by time marching. Limited by the availability of experimental data, validations are performed on 3D simulations of 2D geometries using the Eulerian and Lagrangian methods, respectively. The code proves to be feasible and accurate enough in predicting ice shapes. Finally, an icing simulation result of the M6 wing is presented to illustrate the full 3D capability.
16
Murasiewicz, Halina, et Zdzislaw Jaworski. « Transient CFD simulations of turbulent liquid - liquid flow in a Kenics static mixer. Radial and tangential velocities ». Polish Journal of Chemical Technology 11, no 2 (1 janvier 2009) : 36–40. http://dx.doi.org/10.2478/v10026-009-0021-2.
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Transient CFD simulations of turbulent liquid - liquid flow in a Kenics static mixer. Radial and tangential velocities The results of modelling of the two-phase turbulent flow of a two-phase, liquid-liquid mixture in a Kenics static mixer were reported. Advanced transient simulations were performed using the large eddy simulation (LES) approach and a broader analysis of the velocity field was carried out. The two-phase flow was modelled employing the Eulerian approach in the pseudo-homogeneous version of the mixture model. Three cases were again considered, which differed by the density of the two phases and the simulations were performed for Reynolds number of 10,000. The LES results for the tangential and radial components were compared with those obtained in the steady-state RANS approach.
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Golshan, Roozbeh, Michel Boufadel, Victor Rodriguez, Xiaolong Geng, Feng Gao, Thomas King, Brian Robinson et Andrés Tejada-Martínez. « Oil Droplet Transport under Non-Breaking Waves : An Eulerian RANS Approach Combined with a Lagrangian Particle Dispersion Model ». Journal of Marine Science and Engineering 6, no 1 (15 janvier 2018) : 7. http://dx.doi.org/10.3390/jmse6010007.
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Weaver, Dustin Steven, et Sanja Mišković. « A Study of RANS Turbulence Models in Fully Turbulent Jets : A Perspective for CFD-DEM Simulations ». Fluids 6, no 8 (31 juillet 2021) : 271. http://dx.doi.org/10.3390/fluids6080271.
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This paper presents an analysis of linear viscous stress Favre averaged turbulence models for computational fluid dynamics (CFD) of fully turbulent round jets with a long straight tube geometry in the near field. Although similar work has been performed in the past with very relevant solutions, considerations were not given for the issues and limitations involved with coupling between an Eulerian and Lagrangian phase, such as in fully two-way coupled CFD-DEM. These issues include limitations on solution domain, mesh cell size, wall modelling, and momentum coupling between the two phases in relation to the particles size. Therefore, within these considerations, solutions are provided to the Navier–Stokes equations with various turbulence models using a three-dimensional wedge long straight tube geometry for fully developed turbulence flow. Simulations are performed with a Reynolds number of 13,000 and 51,000 using two different tube diameters. It is found that a modified k-ε turbulence model achieved the most agreeable results for both the velocity and turbulent flow fields between these two flow regimes, while a modified k-ω SST/BSL also provided suitable results.
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Lobanov, Pavel, Maksim Pakhomov et Viktor Terekhov. « Experimental and Numerical Study of the Flow and Heat Transfer in a Bubbly Turbulent Flow in a Pipe with Sudden Expansion ». Energies 12, no 14 (17 juillet 2019) : 2735. http://dx.doi.org/10.3390/en12142735.
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The flow patterns and heat transfer of a downstream bubbly flow in a sudden pipe expansion are experimentally and numerically studied. Measurements of the bubble size were performed using shadow photography. Fluid phase velocities were measured using a PIV system. The numerical model was employed the Eulerian approach. The set of RANS equations was used for modelling two-phase bubbly flows. The turbulence of the carrier liquid phase was predicted using the Reynolds stress model. The peak of axial and radial fluctuations of the carrier fluid (liquid) velocity in the bubbly flow is observed in the shear layer. The addition of air bubbles resulted in a significant increase in the heat transfer rate (up to 300%). The main enhancement in heat transfer is observed after the point of flow reattachment.
20
Chow, T. T., Wenjing Zhang et Jinliang Wang. « Studying the influence of moving vehicle on air pollutant dispersion through environmental chamber ». E3S Web of Conferences 111 (2019) : 02022. http://dx.doi.org/10.1051/e3sconf/201911102022.
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The risk of air pollutants like particulate matters on human beings has been widely reported. One main concern is its health impact on people through direct emission or resuspension. In China with the quick growth in private car ownership, the worries about the influence of the moving vehicles on particulate dispersion is growing. In this study, the influence of a moving object on wick formation and particulate dispersion was investigated. An advanced numerical model was developed, in which the unsteady Eulerian RANS model was applied for simulating the airflow, the modified drift-flux model for modelling particulate dispersion, and the dynamic mesh model for mimicking the moving vehicle. The results show that the vehicular movement induces three noticeable vortexes around the moving body, and the faster the running speed, the stronger the secondary airflow generated.
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Hwang, Byeong-Jo, et Seongki Min. « Numerical Investigation of the Effect of Supersonic Air Temperature on the Mixing Characteristics of Liquid Fuel ». Energies 16, no 1 (2 janvier 2023) : 496. http://dx.doi.org/10.3390/en16010496.
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The effect of supersonic air temperature on the mixing characteristics of liquid hydrocarbon fuel injected into three different supersonic airflows elevated in three steps from 373 K to 673 K was investigated numerically. Compressible Reynolds-averaged Navier–Stokes (RANS) equations were solved together with species conservation equation using ANSYS Fluent for two-phase flow simulations including fuel droplet breakup and evaporation. The turbulence model needed to close the RANS equations used the Shear Stress Transport (SST) k-ω model. The Eulerian–Lagrangian model was employed to track fuel droplets in mainstream air, and the Kelvin–Helmholtz and Rayleigh–Taylor (KH-RT) models were used to simulate the droplet breakup process. Numerical solutions were validated using experimental data. The higher the air temperature, the stronger the streamwise vortices downstream of the pylon. When the air temperature was 373 K, the liquid fuel hardly evaporated, but as the air temperature increased, and the mass fraction of the vaporized fuel and the mixing efficiency increased linearly downstream of the pylon. At air temperatures of 523 K and 673 K, the mixing efficiencies were 10% and 51% at the combustor outlet, respectively. The total pressure loss decreased slightly due to droplet evaporation as the temperature increased from 373 K to 673 K.
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Benim, Ali Cemal, Cansu Deniz Canal et Yakup Erhan Boke. « A Validation Study for RANS Based Modelling of Swirling Pulverized Fuel Flames ». Energies 14, no 21 (4 novembre 2021) : 7323. http://dx.doi.org/10.3390/en14217323.
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A swirling pulverized coal flame is computationally investigated. A Eulerian–Lagrangian formulation is used to describe the two-phase flow. Turbulence is modelled within a RANS (Reynolds averaged numerical simulation) framework. Four turbulence viscosity- (TV) based models, namely the standard k-ε model, realizable k-ε model, renormalization group theory k-ε model, and the shear stress transport k-ω model are used. In addition, a Reynolds stress transport model (RSM) is employed. The models are assessed by comparing the predicted velocity fields with the measurements of other authors. In terms of overall average values, the agreement of the predictions to the measurements is observed to be within the range 20–40%. A better performance of the RSM compared to the TV models is observed, with a nearly twice as better overall agreement to the experiments, particularly for the swirl velocity. In the second part of the investigation, the resolution of the discrete particle phase in modelling the turbulent particle dispersion (TPD) and particle size distribution (SD) is investigated. Using the discrete random walk model for the TPD, it is shown that even five random walks are sufficient for an accuracy that is quite high, with a less than 1% mean deviation from the solution obtained by thirty random walks. The approximation of the measured SD is determined by a continuous Rosin–Rammler distribution function, and inaccuracies that can occur in its subsequent discretization are demonstrated and discussed. An investigation on the resolution of the SD by discrete particle size classes (SC) indicates that 12 SC are required for an accuracy with a less than 1% mean deviation from the solution with 18 SC. Although these numbers may not necessarily be claimed to be sufficiently universal, they may serve as guidance, at least for SD with similar characteristics.
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Sarhadi Zadeh, Ehsan, et Kourosh Hejazi. « Eulerian Oil Spills Model Using Finite-Volume Method with Moving Boundary and Wet-Dry Fronts ». Modelling and Simulation in Engineering 2012 (2012) : 1–7. http://dx.doi.org/10.1155/2012/398387.
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The world production of crude oil is about 3 billion tons per year. The overall objective of the model in present study is supporting the decision makers in planning and conducting preventive and emergency interventions. The conservative equation for the slick dynamics was derived from layer-averaged Navier-Stokes (LNS) equations, averaged over the slick thickness. Eulerian approach is applied across the model, based on nonlinear shallow water Reynolds-averaged Navier-Stokes (RANS) equations. Depth-integrated standard k-εturbulence schemes have been included in the model. Wetting and drying fronts of intertidal zone and moving boundary are treated within the numerical model. A highly accurate algorithm based on a fourth-degree accurate shape function has been used through an alternating-direction implicit (ADI) scheme which separates the operators into locally one-dimensional (LOD) components. The solution has been achieved by the application of KPENTA algorithm for the set of the flow equations which constitutes a pentadiagonal matrix. Hydrodynamic model was validated for a channel with a sudden expansion in width. For validation of oil spill model, predicted results are compared with experimental data from a physical modeling of oil spill in a laboratory wave basin under controlled conditions.
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Mahmoud, Rihab, Mehdi Jangi, Florian Ries, Benoit Fiorina, Johannes Janicka et Amsini Sadiki. « Combustion Characteristics of a Non-Premixed Oxy-Flame Applying a Hybrid Filtered Eulerian Stochastic Field/Flamelet Progress Variable Approach ». Applied Sciences 9, no 7 (29 mars 2019) : 1320. http://dx.doi.org/10.3390/app9071320.
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The oxidation of methane under oxy-fuel combustion conditions with carbon capture is attractive and deserves huge interest towards reducing CO2 and NOx emissions. The current paper reports on the predictions and analysis of combustion characteristics of a turbulent oxy-methane non-premixed flame operating under highly diluted conditions of CO2 and H2 in oxidizer and fuel streams, respectively. These are achieved by applying a novel, well-designed numerical combustion model. The latter consists of a large eddy simulation (LES) extension of a recently suggested hybrid model in Reynolds averaging-based numerical simulation (RANS) context by the authors. It combines a transported joint scalar probability density function (T-PDF) following the Eulerian Stochastic Field methodology (ESF) on the one hand, and a flamelet progress variable (FPV) turbulent combustion model under consideration of detailed chemical reaction mechanism on the other hand. This novel hybrid ESF/FPV approach removes the weaknesses of the presumed-probability density function (P-PDF)-based FPV modeling, along with the solving of associated additional modeled transport equations while rendering the T-PDF computationally less affordable. First, the prediction capability of the LES hybrid ESF/FPV was appraised on the well-known air-piloted methane jet flame (Sandia Flame D). Then, it was assessed in analyzing the combustion properties of a non-premixed oxy-flame and in capturing the CO2 dilution effect on the oxy-fuel flame behavior. To this end, the so-called oxy-flame B3, already numerically investigated in a RANS context, was analyzed. Comparisons with experimental data in terms of temperature, scalar distributions, and scatter plots agree satisfactorily. Finally, the impact of generating the FPV chemistry table under condition of unity Lewis number, even with CO2 dilution, was investigated on the general prediction of the oxy-fuel flame structure, stability and emissions. In particular, it turns out that 68% molar percentage of CO2 leads to 0.39% of CO formation near the burner fuel nozzle and 0.62% at 10 dfuel above the nozzle.
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Pakhomov, Maksim A., et Viktor I. Terekhov. « RANS Modeling of Turbulent Flow and Heat Transfer in a Droplet-Laden Mist Flow through a Ribbed Duct ». Water 14, no 23 (24 novembre 2022) : 3829. http://dx.doi.org/10.3390/w14233829.
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The local structure, turbulence, and heat transfer in a flat ribbed duct during the evaporation of water droplets in a gas flow were studied numerically using the Eulerian approach. The structure of a turbulent two-phase flow underwent significant changes in comparison with a two-phase flow in a flat duct without ribs. The maximum value of gas-phase turbulence was obtained in the region of the downstream rib, and it was almost twice as high as the value of the kinetic energy of the turbulence between the ribs. Finely dispersed droplets with small Stokes numbers penetrated well into the region of flow separation and were observed over the duct cross section; they could leave the region between the ribs due to their low inertia. Large inertial droplets with large Stokes numbers were present only in the mixing layer and the flow core, and they accumulated close to the duct ribbed wall in the flow towards the downstream rib. An addition of evaporating water droplets caused a significant enhancement in the heat transfer (up to 2.5 times) in comparison with a single-phase flow in a ribbed channel.
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Seredyn, Tomasz, Adam Dziubiński et Piotr Jaśkowski. « CFD Analysis of the Fluid Particles Distribution by Means of Aviation Technique ». Transactions on Aerospace Research 2018, no 1 (1 mars 2018) : 67–97. http://dx.doi.org/10.2478/tar-2018-0006.
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Abstract The article describes a computational study, using CFD models, of droplet spray dispersal in the wake of a ‘Turbo Kruk’ airplane up to 500 m downstream. The CFD Reynolds-averaged Navier-Stokes (RANS) models use a Lagrangian (droplet phase) and Eulerian (fluid phase) procedure to predict the droplet trajectories trough the turbulent aircraft wake. The methods described in the work have the potential to improve current models for aerial spraying and will help in the development of new spraying procedures. In this study, the CFD models are used to describe the phenomenon of sprays released from atomizers mounted on the plane. A parametric study of the aircraft model examines the effects of crosswind on the aircraft’s vortex structures and the resulting droplet trajectories. The study shows, that such influence is underestimated in the current models. A comparison of the present results to AGDISP predictions is provided.
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Kohlstädt, Sebastian, Michael Vynnycky, Stephan Goeke et Andreas Gebauer-Teichmann. « On Determining the Critical Velocity in the Shot Sleeve of a High-Pressure Die Casting Machine Using Open Source CFD ». Fluids 6, no 11 (28 octobre 2021) : 386. http://dx.doi.org/10.3390/fluids6110386.
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This paper investigates the critical plunger velocity in high-pressure die casting during the slow phase of the piston motion and how it can be determined with computational fluid dynamics (CFD) in open source software. The melt-air system is modelled via an Eulerian volume-of-fluid approach, treating the air as a compressible perfect gas. The turbulence is treated via a Reynolds-averaged Navier Stokes (RANS) approach that uses the Menter SST k-ω model. Two different strategies for mesh motion are presented and compared against each other. The solver is validated via analytical models and empirical data. A method is then presented to determine the optimal velocity using a two-dimensional (2D) mesh. As a second step, it is then discussed how the results are in line with those obtained for an actual, industrially relevant, three-dimensional (3D) geometry that also includes the ingate system of the die.
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Пахомов, М. А., et В. И. Терехов. « Влияние внезапного сужения плоского канала на вынужденную конвекцию в турбулентном газокапельном течении ». Письма в журнал технической физики 49, no 7 (2023) : 16. http://dx.doi.org/10.21883/pjtf.2023.07.54915.19453.
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Numerical modeling of the flow structure and heat transfer in a gas-droplet turbulent flow in a duct with forward-facing step is carried out. The two-dimensional RANS equations are used in the numerical solution. The Eulerian two-fluid approach is used for describing the flow dynamics and heat transfer in the gaseous and dispersed phases. The turbulence of the carrier phase is described using an elliptical Reynolds stress model with taking the presence of dispersed phase. It is shown that finely-dispersed droplets are involved in the separation recirculation motion of the gas phase. The addition of evaporating droplets to a single-phase turbulent flow in the forward-facing step leads to a significant intensification of heat transfer (more than 2 times) compared to a single-phase air flow, all other things being equal. This effect is enhanced with an increase in the initial mass fraction of the water droplets.
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Sinha, Nityanand, et Roozbeh Golshan. « Material Transport under a Wave Train in Intarcation with Constant Wind : A Eulerian RANS Approach Combined with a Lagrangian Particle Dispersion Model ». Fluids 3, no 2 (5 juin 2018) : 40. http://dx.doi.org/10.3390/fluids3020040.
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Cando, Edgar, An Yu, Lei Zhu, Juan Liu, Li Lu, Victor Hidalgo et Xian Wu Luo. « Unsteady numerical analysis of the liquid-solid two-phase flow around a step using Eulerian-Lagrangian and the filter-based RANS method ». Journal of Mechanical Science and Technology 31, no 6 (juin 2017) : 2781–90. http://dx.doi.org/10.1007/s12206-017-0521-6.
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Aprovitola, Andrea, Francesco Aurisicchio, Pasquale Emanuele Di Nuzzo, Giuseppe Pezzella et Antonio Viviani. « Low Speed Aerodynamic Analysis of the N2A Hybrid Wing–Body ». Aerospace 9, no 2 (10 février 2022) : 89. http://dx.doi.org/10.3390/aerospace9020089.
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Reduction of atmospheric emissions is currently a mandatory requirement for aircraft manufacturers. Several studies performed on Blended Wing–Body configurations showed a promising capability of reducing fuel consumption by increasing, at the same time, passengers’ transport capabilities. Although several aerodynamic studies are available at transonic speeds, low-speed evaluations of aerodynamic performances of Blended Wing Body aircrafts are less investigated. In this framework, the present paper deals with the aerodynamic performance of the N2A aircraft prototype at low-Mach number conditions. Aircraft longitudinal aerodynamics is addressed at M∞=0.2 with steady state three-dimensional RANS simulations carried out at two Reynolds numbers equal to 6.60×106 and 1.27×108, respectively. The former refers to an experimental test campaign performed at NASA Langley 14-by-22 foot subsonic tunnel, while the latter is related to free-flight conditions close to an approach and landing phase. Flowfield simulations are performed using the Computational Fluid Dynamic code FLUENT and the SU2 open-source code, currently adopted for research applications. Numerical solutions are validated by using available experimental data with reference to lift, drag, pitching moment and drag polar estimations. Pre-stall and post-stall aerodynamic behaviour through mean flow-field visualization along with the comparison of pressure distributions at several AoAs is addressed. Furthermore, the effect of convective discretization on a numerical solution for SU2 is discussed. Results indicate a good agreement with available experimental predictions. The present study aims to bridge existing computations at a Eulerian low-Mach number, with RANS computations and constitutes a further test-case for SU2 code with respect to a full aircraft configuration.
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Park, Ilryong, Jein Kim, Bugeun Paik et Hanshin Seol. « Numerical Study on Tip Vortex Cavitation Inception on a Foil ». Applied Sciences 11, no 16 (9 août 2021) : 7332. http://dx.doi.org/10.3390/app11167332.
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In this paper, the inception of tip vortex cavitation in weak water has been predicted using a numerical simulation, and a new scaling concept with variable exponent has also been suggested for cavitation inception index. The numerical simulations of the cavitating flows over an elliptic planform hydrofoil were performed by using the RANS approach with a Eulerian cavitation model. To ensure the accuracy of the present simulations, the effects of the turbulence model and grid resolution on the tip vortex flows were investigated. The turbulence models behaved differently in the boundary layer of the tip region where the tip vortex is developed, which resulted in different pressure and velocity fields in the vortex region. Furthermore, the Reynolds stress model for the finest grid showed a better agreement with the experimental data. The tip vortex cavitation inception numbers for the foil, predicted by using both wetted and cavitating flow simulation approaches, were compared with the measured cavitation index values, showing a good correlation. The current cavitation scaling study also suggested new empirical relations as a function of the Reynolds number substitutable for the two classic constant scaling exponents. This scaling concept showed how the scaling law changes with the Reynolds number and provided a proper scaling value for any given Reynolds numbers under turbulent flow conditions.
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Sugianto, Erik, Arif Winarno, Ratna Indriyani et Jeng Horng Chen. « Hull Number Effect in Ship Using Conveyor on Ocean Waste Collection ». Kapal : Jurnal Ilmu Pengetahuan dan Teknologi Kelautan 18, no 3 (26 octobre 2021) : 128–39. http://dx.doi.org/10.14710/kapal.v18i3.40744.
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The increase in ocean waste continues to grow from year to year, especially plastic and solid waste. Various ocean waste collection ships using conveyors exist, both in the form of designs and already in operation, but there has been no research on how many hulls are suitable for ocean waste collectors. This study aims to choose between the three-ship models, namely monohull type U, catamaran type inner flat hull, and trimaran type symmetrical. Assessment is based on ship resistance which relates to fuel consumption and flow distribution relates to ocean waste collection. This research uses Computational Fluid Dynamics (CFD) method which produces resistance, fluid flow velocity contours, and fluid flow patterns. Numerical simulation is based on Reynolds Averaged Navier Stokes (RANS). The turbulent model uses the standard k-epsilon equation. Then the volume of fluid sub-models used is open channel flow. The number of eulerian phases is two. Moreover, formulation of the volume fraction parameters used is an implicit body force. The results show that monohull type U is better than others in easiest to bring ocean waste closer to the conveyor and smallest resistance force. Then symmetric trimaran is faster than others in making ocean waste flow to the conveyor.
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Mahmoud, Rihab, Mehdi Jangi, Benoit Fiorina, Michael Pfitzner et Amsini Sadiki. « Numerical Investigation of an OxyfuelNon-Premixed CombustionUsing a Hybrid Eulerian Stochastic Field/Flamelet Progress Variable Approach : Effects of H2/CO2Enrichment and Reynolds Number ». Energies 11, no 11 (14 novembre 2018) : 3158. http://dx.doi.org/10.3390/en11113158.
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In the present paper, the behaviour of an oxy-fuel non-premixed jet flame is numerically investigated by using a novel approach which combines a transported joint scalar probability density function (T-PDF) following the Eulerian Stochastic Field methodology (ESF) and a Flamelet Progress Variable (FPV) turbulent combustion model under consideration of detailed chemical reaction mechanism. This hybrid ESF/FPV approach overcomes the limitations of the presumed- probability density function (P-PDF) based FPV modelling along with the solving of associated additional modelled transport equations while rendering the T-PDF computationally less demanding. In Reynolds Averaged Navier-Stokes (RANS) context, the suggested approach is first validated by assessing its general prediction capability in reproducing the flame and flow properties of a simple piloted jet flame configuration known as Sandia Flame D. Second, its feasibility in capturing CO2addition effect on the flame behaviour is demonstrated while studying a non-premixed oxy-flame configuration. This consists of an oxy-methane flame characterized by a high CO2 amount in the oxidizer and a significant content of H2 in the fuel stream, making it challenging for combustion modelling. Comparisons of numerical results with experimental data show that the complete model reproduces the major properties of the flame cases investigated and allows achieving the best agreement for the temperature and different species mass fractions once compared to the classical presumed PDF approach.
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Ghosh, Sayan, et R. Ganesh Rajagopalan. « A Computational Study on Rotor and Fuselage Configuration Effect on Rotorcraft Brownout ». Journal of the American Helicopter Society 67, no 1 (1 janvier 2022) : 1–18. http://dx.doi.org/10.4050/jahs.67.012001.
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Rotorcraft brownout is an in-flight visibility restriction caused by clouds of sand and dust particles during landing, takeoff, and near-ground flight operations in arid desert terrain. This complex phenomenon is caused by the entrainment of dust, sand, and ground particles by rotor downwash and is compounded by fuselage geometry and its orientation with respect to the ground. Highly unsteady wind velocities are common in near-ground operations and play a significant role in the particulate cloud's behavior that creates the brownout condition. Experiments and flight tests to understand brownout are challenging, expensive, and risky. Alternatively, computational fluid dynamics (CFD) has been used extensively over the past few decades to study rotorcraft aerodynamics. However, there are additional computational challenges associated with modeling the dust particle transport in a brownout. In this work, a computationally efficient Eulerian-based framework has been developed to model rotorcraft brownout. The flowfield is modeled by Reynolds averaged Navier–Stokes (RANS) equation and is solved using the SIMPLER algorithm. Turbulence properties are modeled using Realizable κ – ε equations, while the rotor is modeled as a momentum source to focus on the global flowfield rather than the flow near the rotors. The Eulerian approach for both the flowfield and the dust transport allows computationally efficient and rapid analysis, taking an order of few hours in a single CPU to a fraction of an hour using GPU-based computation. In this work, results from two sets of experiments are presented. At first, a study on the fuselage's effect on brownout with respect to height for a single-rotor configuration in hover is demonstrated. Next, a study on the brownout characteristics of three rotor–fuselage configurations in hover, namely single-rotor, tandem-rotor, and quad-rotor, is presented. It has been observed that the ground friction velocity profile and flowfield vorticity around the rotorcraft play a significant role in dust cloud behavior. Additionally, the body forces and interference due to the fuselage plays a vital role in the formation of brownout dust clouds. The experiments showed that the quad-rotor is worst affected in terms of size and height of the dust clouds. However, the tandem-rotor has been found to be worst in the terms of average dust density.
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Bogatko, Tatiana V., Aleksandr V. Chinak, Ilia A. Evdokimenko, Dmitriy V. Kulikov, Pavel D. Lobanov et Maksim A. Pakhomov. « The Effect of a Backward-Facing Step on Flow and Heat Transfer in a Polydispersed Upward Bubbly Duct Flow ». Water 13, no 17 (24 août 2021) : 2318. http://dx.doi.org/10.3390/w13172318.
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The experimental and numerical results on the flow structure and heat transfer in a bubbly polydispersed upward duct flow in a backward-facing step are presented. Measurements of the carrier fluid phase velocity and gas bubbles motion are carried out using the PIV/PLIF system. The set of RANS equations is used for modeling the two-phase bubbly flow. Turbulence of the carrier fluid phase is predicted using the Reynolds stress model. The effect of bubble addition on the mean and turbulent flow structure is taken into account. The motion and heat transfer in a dispersed phase is modeled using the Eulerian approach taking into account bubble break-up and coalescence. The method of delta-functions is employed for simulation of distributions of polydispersed gas bubbles. Small bubbles are presented over the entire duct cross-section and the larger bubbles mainly observed in the shear mixing layer and flow core. The recirculation length in the two-phase bubbly flow is up to two times shorter than in the single-phase flow. The position of the heat transfer maximum is located after the reattachment point. The effect of the gas volumetric flow rate ratios on the flow patterns and maximal value of heat transfer in the two-phase flow is studied numerically. The addition of air bubbles results in a significant increase in heat transfer (up to 75%).
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Lai, Chris C. K., John J. Charonko et Katherine Prestridge. « A Kármán–Howarth–Monin equation for variable-density turbulence ». Journal of Fluid Mechanics 843 (27 mars 2018) : 382–418. http://dx.doi.org/10.1017/jfm.2018.125.
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We present a generalisation of the Kármán–Howarth–Monin (K–H–M) equation to include variable-density (VD) effects. The derived equation (i) reduces to the original K–H–M equation when density is a constant and (ii) leads to a VD analogue of the $4/5$-law with the same value of constant ($=4/5$) appearing as the prefactor of the dissipation rate. The equation is employed to understand negative turbulent kinetic energy production in a $\text{SF}_{6}$ turbulent round jet with an initial density ratio of 4.2. From a Reynolds-averaged Navier–Stokes (RANS) perspective, negative production means that the mean flow is strengthened at the expense of the energy of turbulent fluctuations. We show that the associated energy transfer is accomplished by the deformation of smaller turbulent eddies into large ones in the development region of the jet and is captured by the linear scale-by-scale energy transfer term in the VD K–H–M equation. The nonlinear transfer term of the VD K–H–M equation depicts a conventional forward cascade for all eddies having a size less than the Eulerian integral length scale, regardless of their orientation. The net effect is a retarded energy cascade in the non-Boussinesq jet that has not been accounted for by existing turbulence theories. Implications of this observation for turbulence modelling are discussed.
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Gautam, Saroj, Sailesh Chitrakar, Hari Prasad Neopane, W. Bjørn Solemslie et Ole Gunnar Dahlhaug. « Numerical investigation of a Pelton turbine at several operating conditions ». IOP Conference Series : Earth and Environmental Science 1037, no 1 (1 juin 2022) : 012053. http://dx.doi.org/10.1088/1755-1315/1037/1/012053.
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Abstract The use of Computational Fluid Dynamics (CFD) for predicting the flow behaviour in Pelton turbines is limited by the complex nature of the flow, interaction between the jets and interference of the water after the impact on the buckets. Besides, validation of the numerical results in such turbines is usually challenging due to the unsteadiness of the flow properties. Hence, time-dependent analysis with multi-phase models is required for obtaining such solutions. This paper conducts a CFD analysis on a Pelton turbine using RANS based Eulerian scheme. The fluid domain consists of three successive buckets placed in their corresponding circumferential locations, along with a spear valve, which is adjusted for various operating conditions. Such a domain assumes that the interaction of the jet on the buckets takes place for a maximum of three buckets at any particular time. The results of the CFD analysis are compared with the experimental results for all the studied opening conditions. The objective of this work is to build a suitable numerical model that can be applied to any Pelton turbines, such that a complete performance curve of the turbine can be generated. The flow pattern between entry and exit of the bucket obtained from CFD is compared with images taken from a high speed camera in rotating frame of reference. The results of the numerical analysis are found to be in a good agreement with the experimental data.
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Castorrini, Alessio, Alessandro Corsini, Franco Rispoli, Kenji Takizawa et Tayfun E. Tezduyar. « A stabilized ALE method for computational fluid–structure interaction analysis of passive morphing in turbomachinery ». Mathematical Models and Methods in Applied Sciences 29, no 05 (mai 2019) : 967–94. http://dx.doi.org/10.1142/s0218202519410057.
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Computational fluid–structure interaction (FSI) and flow analysis now have a significant role in design and performance evaluation of turbomachinery systems, such as wind turbines, fans, and turbochargers. With increasing scope and fidelity, computational analysis can help improve the design and performance. For example, it can help add a passive morphing attachment (MA) to the blades of an axial fan for the purpose of controlling the blade load and section stall. We present a stabilized Arbitrary Lagrangian–Eulerian (ALE) method for computational FSI analysis of passive morphing in turbomachinery. The main components of the method are the Streamline-Upwind/Petrov–Galerkin (SUPG) and Pressure-Stabilizing/Petrov–Galerkin (PSPG) stabilizations in the ALE framework, mesh moving with Jacobian-based stiffening, and block-iterative FSI coupling. The turbulent-flow nature of the analysis is handled with a Reynolds-Averaged Navier–Stokes (RANS) model and SUPG/PSPG stabilization, supplemented with the “DRDJ” stabilization. As the structure moves, the fluid mechanics mesh moves with the Jacobian-based stiffening method, which reduces the deformation of the smaller elements placed near the solid surfaces. The FSI coupling between the blocks of the fully-discretized equation system representing the fluid mechanics, structural mechanics, and mesh moving equations is handled with the block-iterative coupling method. We present two-dimensional (2D) and three-dimensional (3D) computational FSI studies for an MA added to an axial-fan blade. The results from the 2D study are used in determining the spanwise length of the MA in the 3D study.
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Kohlstädt, Sebastian, Michael Vynnycky et Stephan Goeke. « On the CFD Modelling of Slamming of the Metal Melt in High-Pressure Die Casting Involving Lost Cores ». Metals 11, no 1 (1 janvier 2021) : 78. http://dx.doi.org/10.3390/met11010078.
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This paper uses computational fluid dynamics (CFD), in the form of the OpenFOAM software package, to investigate the forces on the salt core in high-pressure die casting (HPDC) when being exposed to the impact of the inflowing melt in the die filling stage, with particular respect to the moment of first impact—commonly known as slamming. The melt-air system is modelled via an Eulerian volume-of-fluid approach, treating the air as a compressible perfect gas. The turbulence is treated via a Reynolds-averaged Navier Stokes (RANS) approach. The RNG k-ε and the Menter SST k-ω models are both evaluated, with the use of the latter ultimately being adopted for batch computations. A study of the effect of the Courant number, with a view to establishing mesh independence, indicates that meshes which are finer, and time steps that are smaller, than those previously employed for HPDC simulations are required to capture the effect of slamming on the core properly, with respect to existing analytical models and empirical measurements. As a second step, it is then discussed what response should be expected when this force, with its spike-like morphology and small force-time integral, impacts the core. It is found that the displacement of the core due to the spike in the force is so small that, even though the force is high in value, the bending stress inside the core remains below the critical limit for fracture. It can therefore be concluded that, when assuming homogeneous crack-free material conditions, the spike in the force is not failure-critical.
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Cunha, Augusto, Carlos Fragoso, Matheus Tavares, J. Cavalcanti, Marie-Paule Bonnet et David Motta-Marques. « Combined Use of High-Resolution Numerical Schemes to Reduce Numerical Diffusion in Coupled Nonhydrostatic Hydrodynamic and Solute Transport Model ». Water 11, no 11 (31 octobre 2019) : 2288. http://dx.doi.org/10.3390/w11112288.
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In three-dimensional simulations of free-surface flow where the vertical velocities are relevant, such as in lakes, estuaries, reservoirs, and coastal zones, a nonhydrostatic hydrodynamic approach may be necessary. Although the nonhydrostatic hydrodynamic approach improves the physical representation of pressure, acceleration and velocity fields, it is not free of numerical diffusion. This numerical issue stems from the numerical solution employed in the advection and diffusion terms of the Reynolds-averaged Navier–Stokes (RANS) and solute transport equations. The combined use of high-resolution schemes in coupled nonhydrostatic hydrodynamic and solute transport models is a promising alternative to minimize these numerical issues and determine the relationship between numerical diffusion in the two solutions. We evaluated the numerical diffusion in three numerical experiments, for different purposes: The first two experiments evaluated the potential for reducing numerical diffusion in a nonhydrostatic hydrodynamic solution, by applying a quadratic interpolator over a Bilinear, applied in the Eulerian–Lagrangian method (ELM) step-ii interpolation, and the capability of representing the propagation of complex waves. The third experiment evaluated the effect on numerical diffusion of using flux-limiter schemes over a first-order Upwind in solute transport solution, combined with the interpolation methods applied in a coupled hydrodynamic and solute transport model. The high-resolution methods were able to substantially reduce the numerical diffusion in a solute transport problem. This exercise showed that the numerical diffusion of a nonhydrostatic hydrodynamic solution has a major influence on the ability of the model to simulate stratified internal waves, indicating that high-resolution methods must be implemented in the numerical solution to properly simulate real situations.
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Fossi, Alain, Alain DeChamplain et Benjamin Akih-Kumgeh. « Unsteady RANS and scale adaptive simulations of a turbulent spray flame in a swirled-stabilized gas turbine model combustor using tabulated chemistry ». International Journal of Numerical Methods for Heat & ; Fluid Flow 25, no 5 (1 juin 2015) : 1064–88. http://dx.doi.org/10.1108/hff-09-2014-0272.
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Purpose – The purpose of this paper is to numerically investigate the three-dimensional (3D) reacting turbulent two-phase flow field of a scaled swirl-stabilized gas turbine combustor using the commercial computational fluid dynamic (CFD) software ANSYS FLUENT. The first scope of the study aims to explicitly compare the predictive capabilities of two turbulence models namely Unsteady Reynolds Averaged Navier-Stokes and Scale Adaptive Simulation for a reasonable trade-off between accuracy of results and global computational cost when applied to simulate swirl-stabilized spray combustion. The second scope of the study is to couple chemical reactions to the turbulent flow using a realistic chemistry model and also to model the local chemical non-equilibrium(NEQ) effects caused by turbulent strain such as flame stretching. Design/methodology/approach – Standard Eulerian and Lagrangian formulations are used to describe both gaseous and liquid phases, respectively. The computing method includes a two-way coupling in which phase properties and spray source terms are interchanging between the two phases within each coupling time step. The fuel used is liquid jet-A1 which is injected in the form of a polydisperse spray and the droplet evaporation rate is calculated using the infinite conductivity model. One-component (n-decane) and two-component fuels (n-decane+toluene) are used as jet-A1 surrogates. The combustion model is based on the mean mixture fraction and its variance, and a presumed-probability density function is used to model turbulent-chemistry interactions. The instantaneous thermochemical state necessary for the chemistry tabulation is determined by using initially the equilibrium (EQ) assumption and thereafter, detailed NEQ calculations through the steady flamelets concept. The combustion chemistry of these surrogates is represented through a reduced chemical kinetic mechanism (CKM) comprising 1,045 reactions among 139 species, derived from the detailed jet-A1 surrogate model, JetSurf 2.0 using a sensitivity based method, Alternate Species Elimination. Findings – Numerical results of the gas velocity, the gas temperature and the species molar fractions are compared with their experimental counterparts obtained from a steady state flame available in the literature. It is observed that, SAS coupled to the tabulated flamelet-based chemistry, predicts reasonably the main flame trends, while URANS even provided with the same combustion model and computing resources, leads to a poor prediction of the global flame trends, emphasizing the asset of a proper resolution when simulating spray flames. Research limitations/implications – The steady flamelet model even coupled with a robust turbulence model does not reproduce accurately the trend of species with slow oxidation kinetics such as CO and H2, because of the restrictiveness of the solutions space of flamelet equations and the assumption of unity Lewis for all species. Practical implications – This work is adding a contribution for spray flame modeling and can be seen as an extension to the significant efforts for the modeling of gaseous flames using robust turbulence models coupled with the tabulated flamelet-based chemistry approach to considerably reduce computing cost. The exclusive use of a commercial CFD code widely used in the industry allows a direct application of this simulation approach to industrial configurations while keeping computing cost reasonable. Originality/value – This study is useful to engineers interested in designing combustors of gas turbines and others combustion systems fed with liquid fuels.
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Gunawan, Alexander Agung Santoso. « Hubungan Deret Bertingkat Berdasarkan Bilangan Eulerian dengan Operator Beda ». ComTech : Computer, Mathematics and Engineering Applications 2, no 1 (1 juin 2011) : 154. http://dx.doi.org/10.21512/comtech.v2i1.2727.
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Rank series defined as: is a generalization of the fixed rank series (the sum of powers), in which its closed solution has been found empirically by Jacob Bernoulli in 1731. This paper will explore the relationship between rank series and differential operator. To see this relationship, examples for the case m = 1.2 and α = 1.2. are provided.
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Md Isa, Kamariah, Kahar Osman, Nor Fadzilah Othman, Nik Rosli Abdullah et Mohd Norhakem Hamid. « A Multiphase Eulerian-Eulerian CFD Simulation of Fluidized Bed Gasification Using Malaysian Low-Rank Coal-Merit Pila ». Key Engineering Materials 740 (juin 2017) : 163–72. http://dx.doi.org/10.4028/www.scientific.net/kem.740.163.
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A multiphase Eulerian- eulerian model integrating the kinetic theory of granular particle (KTGF) was used to simulate the gasification of Malaysian low- rank coal (LRC), Merit- Pila inside a bubbling fluidised bed (BFB) gasifier. The model used includes the bubbling phenomenon and gasificationprocess that occurs inside a BFB gasifier. The gasification process simulated includes drying, heterogeneous reactions of char combustion, devolatilization, water- gas shift reaction, Boudourd reactionand gas phase homogenous reactions. The results from this model are compared to the results of Merit-Pila coal gasification, from which experimental data is available. Comparison of the pressure profile shows good agreement with experimental results. The temperature distribution shows that the maximum temperature is around 1100K which also shows good agreement with experimental values which is 1087K. Besides that, three out of six species mass fraction which is N2, H2 and CH4 produced similar values with experimental values. This shows the simulation conducted was capable to predict the gasification process of Low- rank coal, namely Merit-Pila.
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Campos, Cláudia Rejane Jacondino de, James Adryani Avelar de Jesus et Luciana Barros Pinto. « Concentração superficial de contaminantes simulada por um Modelo Euleriano de Dispersão utilizando perfis de vento obtidos pelos modelos OML e RAMS ». Anuário do Instituto de Geociências 30, no 2 (1 décembre 2007) : 23–30. http://dx.doi.org/10.11137/2007_2_23-30.
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In this work was tested the use of output data from Regional Atmospheric Modeling System (RAMS) as input to an Eulerian Dispersion Model (EDM). Specifically was compared the ground level cross-wind integrated concentration simulated by EDM, using an eddy diffusivity valid to the Convective Boundary Layer (CBL) and two wind profiles: the first obtained by the Operationelle Meteorologiske Luftkvalitetsmodeller model (OML) and the second generated by RAMS mesoscale model. To accomplish the simulations with EDM were used data collected on the 07/06/1979 during Copenhagen tracer experiment (emission rate, source height, convective velocity scale, CBL height, friction velocity, Monin-Obukhov length in the surface layer and roughness length). The performance of the two simulations was tested confronting the ground level cross-wind integrated concentration generated with those observed in referred experiment. For simple topography area, such as the study area, the results showed that the use of a diagnosis model (OML) or a prognostic model (RAMS) to simulate the wind profile didn't generate great differences between ground level cross-wind integrated concentration simulated by EDM.
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Kiss, Viktor, et Lilla Tóthmérész. « Chip-firing games on Eulerian digraphs andNP-hardness of computing the rank of a divisor on a graph ». Discrete Applied Mathematics 193 (octobre 2015) : 48–56. http://dx.doi.org/10.1016/j.dam.2015.04.030.
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Dhariwal, Rohit, Sarma L. Rani et Donald L. Koch. « Stochastic theory and direct numerical simulations of the relative motion of high-inertia particle pairs in isotropic turbulence ». Journal of Fluid Mechanics 813 (17 janvier 2017) : 205–49. http://dx.doi.org/10.1017/jfm.2016.859.
Texte intégralRésumé :
The relative velocities and positions of monodisperse high-inertia particle pairs in isotropic turbulence are studied using direct numerical simulations (DNS), as well as Langevin simulations (LS) based on a probability density function (PDF) kinetic model for pair relative motion. In a prior study (Rani et al., J. Fluid Mech., vol. 756, 2014, pp. 870–902), the authors developed a stochastic theory that involved deriving closures in the limit of high Stokes number for the diffusivity tensor in the PDF equation for monodisperse particle pairs. The diffusivity contained the time integral of the Eulerian two-time correlation of fluid relative velocities seen by pairs that are nearly stationary. The two-time correlation was analytically resolved through the approximation that the temporal change in the fluid relative velocities seen by a pair occurs principally due to the advection of smaller eddies past the pair by large-scale eddies. Accordingly, two diffusivity expressions were obtained based on whether the pair centre of mass remained fixed during flow time scales, or moved in response to integral-scale eddies. In the current study, a quantitative analysis of the (Rani et al. 2014) stochastic theory is performed through a comparison of the pair statistics obtained using LS with those from DNS. LS consist of evolving the Langevin equations for pair separation and relative velocity, which is statistically equivalent to solving the classical Fokker–Planck form of the pair PDF equation. Langevin simulations of particle-pair dispersion were performed using three closure forms of the diffusivity – i.e. the one containing the time integral of the Eulerian two-time correlation of the seen fluid relative velocities and the two analytical diffusivity expressions. In the first closure form, the two-time correlation was computed using DNS of forced isotropic turbulence laden with stationary particles. The two analytical closure forms have the advantage that they can be evaluated using a model for the turbulence energy spectrum that closely matched the DNS spectrum. The three diffusivities are analysed to quantify the effects of the approximations made in deriving them. Pair relative-motion statistics obtained from the three sets of Langevin simulations are compared with the results from the DNS of (moving) particle-laden forced isotropic turbulence for $St_{\unicode[STIX]{x1D702}}=10,20,40,80$ and $Re_{\unicode[STIX]{x1D706}}=76,131$. Here, $St_{\unicode[STIX]{x1D702}}$ is the particle Stokes number based on the Kolmogorov time scale and $Re_{\unicode[STIX]{x1D706}}$ is the Taylor micro-scale Reynolds number. Statistics such as the radial distribution function (RDF), the variance and kurtosis of particle-pair relative velocities and the particle collision kernel were computed using both Langevin and DNS runs, and compared. The RDFs from the stochastic runs were in good agreement with those from the DNS. Also computed were the PDFs $\unicode[STIX]{x1D6FA}(U|r)$ and $\unicode[STIX]{x1D6FA}(U_{r}|r)$ of relative velocity $U$ and of the radial component of relative velocity $U_{r}$ respectively, both PDFs conditioned on separation $r$. The first closure form, involving the Eulerian two-time correlation of fluid relative velocities, showed the best agreement with the DNS results for the PDFs.
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Ye, Xiong-Fei, Kai-Chun Chang, Chul-Woo Kim, Harutoshi Ogai, Yoshinobu Oshima et O. S. Luna Vera. « Flow Analysis and Damage Assessment for Concrete Box Girder Based on Flow Characteristics ». Sustainability 11, no 3 (29 janvier 2019) : 710. http://dx.doi.org/10.3390/su11030710.
Texte intégralRésumé :
For a system such as the concrete structure, flow can be the dynamic field to describe the motion, interactions, or both in dynamic or static (Eulerian description) states. Further, various kinds of flow propagate through it from the very start to the end of its lifecycle (Lagrangian description) accompanied by rains, winds, earthquakes, and so forth. Meanwhile, damage may occur inside the structure synchronously, developing from micro- to macro-scale damage, and eventually destroy the structure. This study was conducted to clarify the content of flow which has been implicitly used in the damage detection, and to propose a flow analysis framework based on the combination data space and the theory of dissipative structure theory specifically for nondestructive examination in structural damage detection, which can theoretically standardize the mechanism by which flow characteristics vary, the motion of the structure, or the swarm behavior of substructures in engineering. In this paper, a destructive experiment (static loading experiment) and a following nondestructive experiment (impact hammer experiment) were conducted. According to the experimental data analysis, the changing of flow characteristics shows high sensitivity and efficient precision to distinguish the damage exacerbations in a structure. According to different levels of interaction (intensity) with the structure, the information flow can be divided into two categories: Destructive flow and nondestructive flow. The method used in this research is named as a method of “flow analysis based on flow characteristics”, i.e., “FC-based flow analysis”.
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Finch, D. P., P. I. Palmer et M. Parrington. « Origin, variability and age of biomass burning plumes intercepted during BORTAS-B ». Atmospheric Chemistry and Physics 14, no 24 (23 décembre 2014) : 13789–800. http://dx.doi.org/10.5194/acp-14-13789-2014.
Texte intégralRésumé :
Abstract. We use the GEOS-Chem atmospheric chemistry transport model to interpret aircraft measurements of carbon monoxide (CO) in biomass burning outflow taken during the 2011 BORTAS-B campaign over eastern Canada. The model has some skill reproducing the observed variability, with a Spearman's rank correlation rs = 0.65, but has a positive negative bias for observations <100 ppb and a negative bias for observations > 300 ppb. We find that observed CO variations are largely due to fires over Ontario, as expected, with smaller and less variable contributions from fossil fuel combustion from eastern Asia and NE North America. To help interpret observed variations of CO we develop a Eulerian effective physical age of emissions (A) metric, accounting for mixing and chemical decay, which we apply to pyrogenic emissions of CO. We find that during BORTAS-B the age of emissions intercepted over Halifax, Nova Scotia is typically 4–11 days, and on occasion as young as two days. We show that A is typically 1–5 days older than the associated photochemical ages inferred from co-located measurements of different hydrocarbons. We find that the frequency distribution of differences between the age measures (Δτ) in plumes (defined by CH3CN > 150 ppt) peaks at 3 days. This corresponds to a chemical retardation of 50%. We find a strong relationship in biomass burning plumes between A and Δτ (r2 = 0.80), which is not present outwith these plumes (r2 = 0.28). We argue that these observed relationships, together with a robust observed relationship between CO and black carbon aerosol during BORTAS-B (r2 > 0.7), form the basis of indirect evidence that aerosols co-emitted with gases during pyrolysis markedly slowed down the plume photochemistry during BORTAS-B with respect to photochemistry at the same latitude and altitude in clear skies.
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Sbai. « Well Rate and Placement for Optimal Groundwater Remediation Design with A Surrogate Model ». Water 11, no 11 (25 octobre 2019) : 2233. http://dx.doi.org/10.3390/w11112233.
Texte intégralRésumé :
A new surrogate-assisted optimization formulation for groundwater remediation design was developed. A stationary Eulerian travel time model was used in lieu of a conservative solute transport model. The decision variables of the management model are well locations and their flow rates. The objective function adjusts the residence time distribution between all pairs of injection-production wells in the remediation system. This goal is achieved by using the Lorenz coefficient as an effective metric to rank the relative efficiency of many remediation policies. A discrete adjoint solver was developed to provide the sensitivity of the objective function with respect to changes in decision variables. The quality management model was checked with simple solutions and then applied to hypothetical two- and three-dimensional test problems. The performance of the simulation-optimization approach was evaluated by comparing the initial and optimal remediation designs using an advective-dispersive solute transport simulator. This study shows that optimal designs simultaneously delay solute transport breakthrough at pumping wells and improve the sweep efficiency leading to smaller cleanup times. Well placement optimization in heterogeneous porous media was found to be more important than well rate optimization. Additionally, optimal designs based on two-dimensional models were found to be more optimistic suggesting a direct use of three-dimensional models in a simulation-optimization framework. The computational budget was drastically reduced because the proposed surrogate-based quality management model is generally cheaper than one single solute transport simulation. The introduced model could be used as a fast, but first-order, approximation method to estimate pump-and-treat capital remediation costs. The results show that physically based low-fidelity surrogate models are promising computational approaches to harness the power of quality management models for complex applications with practical relevance.