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direct numerical simulation of settling hydrodynamics in system of bidisperse spherical particles

POWDER TECHNOLOGY 2025年 457卷

作者： Khan, Muhammad Faraz Hamid, Adnan Nadeem, Muhammad Ullah, Atta Pakistan Inst Engn & Appl Sci Dept Chem Engn Islamabad 45650 Pakistan

In this study, direct numerical simulations with an enhanced Smooth Profile Method was employed to investigate the settling dynamics of bidisperse spherical particles undergoing gravitational sedimentation. Under the influence of gravity, large particles composed of joint smaller spherical beads settle in a Newtonian fluid. The concentration ratio effect of large to small particles within Stokes regime was studied. The overall system volume fraction phi is maintained at 0.1, while the volume fraction of large particles, denoted as , is varied from 0.001 0.5. The simulation results reveal notable changes in the radial distribution function. The height of the first peak decreases upon increase in the of large particles concentration. Meanwhile, a second peak emerges and progressively grows in prominence. The average system sedimentation velocity of the exhibits an increasing trend with an increase in . The drag coefficient of the system decreases as increases. It is also observed that the temporal auto correlation function in axial direction intensifies as increase in .

关键词： Sedimentation Bidisperse particle Smooth profile method direct numerical simulation

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direct numerical simulation of collision events in flotation under the influence of gravity

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INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 2025年 188卷

作者： Tiedemann, Benedikt Froehlich, Jochen Tech Univ Dresden Inst Fluid Mech George Bahr Str 3C D-01062 Dresden Germany HZDR Innovat GmbH Bautzener Landst 400 D-01328 Dresden Germany

Collisions between particles and bubbles are decisive for the performance of flotation processes. In this work direct numerical simulations of a prototypical gravitation-driven flotation process are presented with bubbles fully resolved and modelled as rigid spheres while the solid-phase is represented as point-particles. Key bubble and particle parameters correspond to realistic setups and are varied to study their effect on the collision rate. The study addresses the main influencing parameters, such as bubble diameter, gas hold-up, particle diameter, and particle density. Locally around the bubble significant differences of the collision behaviour exist. Most collisions occur on the upper bubble half, but some also on the lower bubble half. This is caused by a high particle-bubble relative velocity towards the bubble from the upper bubble half and an accumulation of particles at these locations as they deviate around the bubble. The paper provides reference data for flotation modelling.

关键词： Flotation Collision Particles Bubbles Three-phase flow direct numerical simulation

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direct numerical simulation of film boiling around a superheated sphere immersed in a subcooled liquid

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2025年 239卷

作者： Bourdon, Gauthier Tanguy, Sebastien Airiau, Christophe Univ Toulouse IMFT CNRS UMR 5502 UPSINPT Toulouse France

Film boiling around immersed objects in a subcooled liquid is critical in various engineering applications and offer many scientific issues. After presenting a numerical solver able to simulate film boiling around a solid obstacle and some preliminary validations of this solver, we propose a comprehensive study based on the direct numerical simulation (DNS) to investigate accurately on the dynamical and heat transfer effects inside the vapor film. After defining two Jakob numbers related respectively to the wall superheat and to the liquid, a parametric study is performed by varying both dimensionless numbers. The simulations allow to visualize the flow structure inside the vapor film and to predict angular variations of the local Nusselt number along the solid wall. In particular, spatial distributions of the local heat flux, related to variations of the film thickness along the solid obstacle, are observed with higher values at the bottom part of the sphere due to buoyancy effect. The simulations also provide accurate data on the global Nusselt number variation with respect to the Jakob numbers and confirm the dominance of conduction heat transfer inside the vapor film. Finally, the study also explores the equilibrium between vaporization and condensation processes which leads to the stabilization of the vapor film around the solid obstacle. This research enhances the understanding of subcooled film boiling and offers new data for film boiling model validation.

关键词： Film boiling Heat transfer Subcooled liquid direct numerical simulation Level set/Ghost Fluid method

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direct numerical simulation of dispersion and mixing in gas-liquid Dean-Taylor flow with influence of a 90° bend

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CHEMICAL ENGINEERING SCIENCE 2025年 301卷

作者： Mierka, Otto Muenster, Raphael Surkamp, Julia Turek, Stefan Kockmann, Norbert TU Dortmund Univ Inst Appl Math LS3 Dept Math Vogelpothsweg 87 D-44227 Dortmund Germany TU Dortmund Univ Dept Biochem & Chem Engn Lab Equipment Design Emil Figge Str 68 D-44227 Dortmund Germany

Gas-liquid capillary flow finds widespread applications in reaction engineering, owing to its ability to facilitate precise control and efficient mixing. Incorporating compact and regular design with Coiled Flow Inverter (CFI) enhances process efficiency due to improved mixing as well as heat and mass transfer leading to a narrow residence time distribution. The impact of Dean and Taylor flow phenomena on mixing and dispersion within these systems underscores their significance, but is still not yet fully understood. direct numerical simulation based on finite element method enables full 3D resolution of the flow field and detailed examination of laminar flow profiles, providing valuable insights into flow dynamics. Notably, the deflection of flow velocity from the center axis contributes is followed by tracking of particle with defined starting positions, aiding in flow visualization and dispersion characterization. In this CFD study, the helical flow with the influence of the centrifugal force and pitch (Dean flow) as well as the capillary two-phase flow (Taylor bubble) is described and characterized by particle dispersion and related histograms. Future prospects in this field include advancements in imaging techniques to capture intricate flow patterns, as well as refined particle tracking methods to better understand complex flow behavior.

关键词： Gas-liquid capillary flow Dean flow Taylor flow direct numerical simulation Finite element method Particle dispersion measurement

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Effects of Damkohler Number on Lean Premixed Jet Flames in Crossflow Using direct numerical simulation

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COMBUSTION SCIENCE AND TECHNOLOGY 2025年第5期197卷 923-943页

作者： Cheng, Mengzhen Wang, Haiou Luo, Kun Fan, Jianren Zhejiang Univ Key Lab Clean Energy & Carbon Neutral Zhejiang Pro Hangzhou Peoples R China Zhejiang Univ State Key Lab Clean Energy Utilizat Hangzhou Peoples R China Zhejiang Univ Key Lab Clean Energy & Carbon Neutral Zhejiang Pro Hangzhou 310027 Peoples R China

In the present work, lean premixed jet flames in crossflow were studied using direct numerical simulation to explore the effects of Damkohler numbers ($Da$Da) on turbulence and flame characteristics. The configuration is based on an experiment, where a jet of lean premixed ethylene-air mixtures ($\phi $phi = 0.6) was injected into a hot vitiated crossflow. The case with a higher and lower Da is denoted as case Da+ and case Da-, respectively. It was found that the turbulence is weakened around the reaction zone of case $Da + $Da+. In contrast, the turbulence of case $Da - $Da- is barely influenced by heat release. The vorticity dynamics are examined with the enstrophy transport equation budget terms, and the viscous dissipation term is the main sink for both cases. The windward and leeward flame branches of case $Da + $Da+ are dominated by auto-ignition and premixed flame propagation respectively, while the auto-ignition and flame propagation modes coexist on the leeward flame branch of case $Da - $Da-. The scalar gradient magnitude in the leeward branch is generally lower compared with the windward branch so that the flame is overall thicker. The normal strain rate is negative, which tends to enhance the scalar gradient, but it becomes positive on the leeward side of case $Da + $Da+, which is influenced by the alignment between the scalar gradient and the principal strain rates.

关键词： Jet in crossflow Lean premixed combustion Damkohler numbers direct numerical simulation

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Effect of liquid flux on wetting behavior in slender trickle bed reactors: A particle-resolved direct numerical simulation study

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CHEMICAL ENGINEERING SCIENCE 2025年 303卷

作者： Tavanaei, A. Rieder, D. R. Baltussen, M. W. Buist, K. A. Kuipers, J. A. M. Eindhoven Univ Technol Dept Chem Engn & Chem Multiphase Reactors Grp POB 513 NL-5600 MB Eindhoven Netherlands

Slender trickle beds play a crucial role in various industrial processes involving gas-liquid-solid systems. Understanding the wetting characteristics is vital for optimizing their performance and efficiency. In this study, we employ a particle-resolved Computational Fluid Dynamics approach combining the Volume of Fluid (VoF) method for gas-liquid interactions and a second-order implicit Immersed Boundary Method (IBM) for fluid-solid interactions. The particle wettability is modeled by imposing a contact angle boundary condition at the gas- liquid-solid interface. The impact of the liquid flux on the wetting patterns and the rate of liquid penetration depth within the slender trickle bed is studied. The results show two main mechanisms of penetration through the bed: gravitation and inertia driven. The penetration of the liquid in the bed is driven by gravity when the liquid flux is low and the inertia is diminished in the top of the bed. This results in enhanced wetting from the onset of the penetration. If the inertia is high (high liquid flux), the initial liquid penetration is fast and spreading in the bed only occurs after full penetration of the bed.

关键词： Trickle bed Wetting direct numerical simulation Volume of fluid

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A supercritical carbon dioxide cooling heat transfer machine learning prediction model based on direct numerical simulation

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INTERNATIONAL COMMUNICATIONS IN HEAT AND MASS TRANSFER 2025年 163卷

作者： Wu, Dingchen Wei, Mingshan Tian, Ran Zhao, Yihang Guo, Jianshe Beijing Inst Technol Sch Mech Engn Beijing 100081 Peoples R China AVIC Jonhon Optron Technol CO LTD Henan Key Lab Optomechatron Integrated Interconnec Luoyang 471003 Peoples R China China Univ Min & Technol Beijing Sch Mech & Elect Engn Beijing 100083 Peoples R China Beijing Inst Technol Chongqing Innovat Ctr Chongqing 401120 Peoples R China Zhejiang Univ Ocean Coll Opt Commun Lab Zhoushan 316021 Peoples R China

The severe thermo-physical properties variations of supercritical fluids in the vicinity of the critical point lead to difficulty in heat transfer prediction. In this paper, a novel prediction model for supercritical CO2 (sCO2) cooling heat transfer is proposed, integrating a direct numerical simulation (DNS) database with the CatBoost algorithm. A high-precision heat transfer prediction database was established based on DNS data (8192 data points in total). The feature parameters were screened utilizing the random forest feature importance method. More importantly, a newly dimensionless parameter, Re-0.9 pi A, was selected as one of the feature parameters. Re-0.9 pi A represents the impact of near-wall acceleration caused by buoyancy, and it demonstrated the highest feature importance during training and screening processes. Based on the selected ten characteristic parameters, a robust data-driven heat transfer prediction model for sCO2 was developed. The CatBoost algorithm outperformed the other three widely used machine learning algorithm s across training sets, testing sets, and actual predictions, achieving a mean absolute percentage error reduction of up to 22.69 %. Through comparison with 6 traditional heat transfer correlations, the results showed that the CatBoost-based sCO2 cooling heat transfer prediction model exhibits superior training speed and predictive accuracy, with a maximum relative error of merely 6.57 %. Moreover, when validated through experimental data with large Reynolds number, this model still has the highest accuracy, with 91.3 % of the data sets having a prediction accuracy within +/- 30 % for the Nusselt number.

关键词： Supercritical carbon dioxide direct numerical simulation Cooling heat transfer Machine learning

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The effects of fluid-solid conjugation on flow and heat transfer of supercritical water: Perspective from direct numerical simulation

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INTERNATIONAL JOURNAL OF HEAT AND MASS TRANSFER 2025年 242卷

作者： Bai, Yifan Wang, Han Wu, Jinghui Liu, Minyun Lyu, Haicai Huang, Yanping North China Elect Power Univ Sch Nucl Sci & Engn Beijing 102206 Peoples R China Nucl Power Inst China CNNC Key Lab Nucl Reactor Thermal Hydraul Technol Chengdu 610041 Peoples R China

An in-depth investigation into the flow and heat transfer characteristics of supercritical water (SCW) is essential for designing and operating Supercritical Water-Cooled Reactor (SCWR) systems. Currently, the great majority of existing direct numerical simulations (DNS) utilize boundary conditions without solid domain in studying the thermal-hydraulic performance of supercritical fluids. However, in practical applications, the fluid-solid conjugation may significantly affect the flow and heat transfer, especially in the near-wall region. The present study utilized a DNS solver implemented in OpenFOAM to examine the effect of fluid-solid conjugation on SCW in vertical and horizontal circular pipes. The wall temperature, mean velocity, instantaneous fluctuations, and turbulence statistics were compared and analyzed under both non-conjugate and conjugate conditions. It was found that in vertical upward flow with conjugate heat transfer, the wall temperature was slightly higher than that of non-conjugate heat transfer, leading to a more pronounced heat transfer deterioration. Temperature fluctuations at the wall were significantly suppressed by the solid domain, weakening the turbulence and heat transfer. In horizontal flows, under non-conjugate conditions, severe heat transfer deterioration occurred at the top generatrix due to buoyancy effects, resulting in a highly uneven circumferential distribution in the wall temperature. When the solid domain is taken into consideration, heat conduction within the solid domain redistributed the heat from the top to the sides, leading to a significant reduction in heat flux at the top. The decreased heat flux lowered the wall temperature and alleviated its uneven distribution, notably enhancing the heat transfer in the top region.

关键词： direct numerical simulation Supercritical water Conjugate heat transfer

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direct numerical simulation of soot break-through in turbulent non-premixed flames

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COMBUSTION AND FLAME 2025年 275卷

作者： Scialabba, Gandolfo Davidovic, Marco Attili, Antonio Pitsch, Heinz Rhein Westfal TH Aachen Inst Combust Technol D-52056 Aachen Germany Univ Edinburgh Inst Multiscale Thermofluids Sch Engn Edinburgh EH9 3FD Scotland

Soot break-through, or "leakage", is the transport of soot particles into fuel-lean regions leading to smoke emissions even when the global equivalence ratio is below unity. Under turbulent conditions, this phenomenon is affected by small-scale mixing, and a better understanding of the non-linear interactions between soot and gas-phase is crucial to improving the prediction of the existing reduced-order model in case of soot break-through. To this end, three direct numerical simulations (DNSs) of temporally evolving turbulent non- premixed jet flames have been performed to study the later stages of soot evolution in turbulent flames. Various degrees of soot break-through are obtained by enforcing three different levels of flame extinction by rescaling the geometry and flow conditions, resulting in a variation in Damk & ouml;hler number, while the Reynolds number remains constant. The simulations employ a detailed chemical mechanism for the gas phase chemistry and a moment method for modeling the soot number density function evolution. Both soot evolution and turbulence-chemistry-soot interaction are discussed in mixture fraction space and along Lagrangian trajectories in physical space. The results reveal that soot break-through is strongly correlated with both high mixture fraction dissipation rates and strong soot transport in mixture fraction space. Due to the higher mixture fraction dissipation rate, the lowest Damk & ouml;hler number case exhibits more significant extinction, allowing significant soot break-through. Additionally, soot particles in the lean regions are shown to be smaller than those inside the flame due to the smaller residence times in the fuel-rich growth regions, with a significant probability of leaked soot particles at incipient size. From the Lagrangian statistics, the ratio of the mixture fraction diffusion rate and soot oxidation rate constant is shown to be a suitable parameter to identify soot break-through events. Overall, soot break-

关键词： direct numerical simulation Soot Oxidation Turbulent Non-premixed

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direct numerical simulation studies of spray jet flames in hot vitiated crossflow

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FUEL 2025年 389卷

作者： Meng, Qian Wang, Haiou Chang, Zhuchuan Cheng, Mengzhen Huang, Ziwei Luo, Kun Fan, Jianren Zhejiang Univ State Key Lab Clean Energy Utilizat Hangzhou 310027 Peoples R China

In the present study, spray jet flames in hot vitiated crossflow were investigated using three-dimensional direct numerical simulations (DNS). The dispersed droplets were tracked based on the Lagrangian framework, while the continuous gas phase was solved in an Eulerian way. The spray jets were injected perpendicularly into vitiated crossflow. A reduced two-step kerosene/air reaction mechanism was used as the chemistry model. Three cases were simulated with different droplet sizes and velocities, while the global equivalence ratio was fixed at unity. In the cases with large droplets, two flame branches on the windward side were identified, including the inner windward flame, which is close to the center jet, and the outer windward flame, which is near the crossflow. The heat release rate for the leeward branch of the flame is relatively low compared to that for the windward branch in all cases. Pocket-like leeward reaction zones were observed in the cases with large droplets. The species budget analysis was employed to characterize the flame stabilization mechanism. Auto-ignition plays a key role in the stabilization of the windward flame for the case with small droplets. In contrast, for the cases with large droplets, the inner windward flame is stabilized mainly by flame propagation, and in the outer windward flame, auto-ignition is prevailing. The combustion modes were examined. It was shown that the contribution of premixed combustion decreases with increasing droplet size and velocity, and non-premixed combustion prevails in the cases with large droplets. Strong droplet/flame interactions were observed in the DNS. It was shown that for the cases with large droplets, the complex motion and evaporation behaviors of droplets injected from different locations lead to the formation of the two flame branches on the windward side. Particularly, droplets injected near the hot vitiated crossflow evaporate quickly and tend to follow the jet, resulting in the formation of

关键词： Spray jet in vitiated crossflow Turbulent combustion Droplet/flame interactions direct numerical simulation

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