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Accurate calculation of bubble and droplet properties in diffuse-interface two-phase simulations

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arXiv 2025年

作者： Nathan, Pranav J. Jain, Suhas S. Flow Physics and Computational Science Lab George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology AtlantaGA United States

In this paper, we address the challenge of accurately calculating droplet/bubble properties (e.g., volume, number) in diffuse-interface two-phase flow simulations. Currently, flood-fill algorithms can truncate a significant portion of the volume of droplets/bubbles contained within the diffuse interface region or artificially merge multiple droplets/bubbles. This error is also dependent on the volume fraction cutoff value, which is typically chosen to be 0.5 arbitrarily, in the flood-fill algorithms. We propose a simple volume-correction approach that incorporates an analytical approximation of the truncated volume to correct for the missing droplet/bubble volumes. This proposed method results in accurately recovering the dispersed phase volumes with minimal volume error over a wide range of volume fraction cutoff values;and hence, can also accurately recover the number of droplets/bubbles. This can be a valuable tool for accurate calculation of drop/bubble size distributions for analysis and for Eulerian-to-Lagrangian conversion of the dispersed phase in multi-scale modeling approaches. © 2025, CC BY.

关键词： Two phase flow

Stationary states of forced two-phase turbulence

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arXiv 2025年

作者： Jain, Suhas S. Elnahhas, Ahmed Flow Physics and Computational Science Lab George W. Woodruff School of Mechanical Engineering Georgia Institute of Technology GA United States Center for Turbulence Research Stanford University CA United States

In this work, we perform numerical simulations of forced two-phase isotropic turbulence to study the stationary states of a two-phase mixture. We first formulate three different approaches to force a two-phase turbulent flow that maintains a constant (a) mixture kinetic energy, (b) mixture kinetic energy + surface energy, and (c) individual phase kinetic energy, and study their effect on the final stationary state of the system. We show that forcing the two-phase system eliminates the arbitrariness associated with the initialization of the second phase in two-phase turbulence simulations. Next, we study the global statistics of the two-phase mixture in the stationary state for varying density ratios (10−3 to 103) and viscosity ratios (10−3 to 103), void fraction (dilute to dense regimes), and Weber numbers (breakup and non-breakup regimes). We utilize a spatial filtering approach, that is applicable for the general case of incompressible/compressible two-phase flows, to compute the energy spectra of each of the phases and study the turbulent kinetic energy distribution across scales. We find that the interface behaves as a soft wall, inhibiting the accommodation of eddies inside the dispersed phase. Finally, we show that bubbles and drops exhibit different turbulent characteristics for the same global conditions of the carrier phase, with bubbles exhibiting higher turbulent intensities inside them and droplets behaving ballistically, similar to solid particles. This study acts as a foundational work on stationary two-phase turbulence, which can be used for further analysis and the development of subgrid-scale models for larger-scale simulations of two-phase turbulent flows. © 2025, CC BY.

关键词： Wakes

Adaptive Growing Randomized Neural Networks for Solving Partial Differential Equations

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arXiv 2024年

作者： Dang, Haoning Wang, Fei Jiang, Song School of Mathematics and Statistics Xi’an Jiaotong University Shaanxi Xi’an710049 China School of Mathematics and Statistics State Key Laboratory of Multiphase Flow in Power Engineering Xi’an Jiaotong University Shaanxi Xi’an710049 China Institute of Applied Physics and Computational Mathematics Beijing100088 China

Randomized neural network (RNN) methods have been proposed for solving various partial differential equations (PDEs), demonstrating high accuracy and efficiency. However, initializing the fixed parameters remains a challenging issue. Additionally, RNNs often struggle to solve PDEs with sharp or discontinuous solutions. In this paper, we propose a novel approach called Adaptive Growing Randomized Neural Network (AG-RNN) to address these challenges. First, we establish a parameter initialization strategy based on frequency information to construct the initial RNN. After obtaining a numerical solution from this initial network, we use the residual as an error indicator. Based on the error indicator, we introduce growth strategies that expand the neural network, making it wider and deeper to improve the accuracy of the numerical solution. A key feature of AG-RNN is its adaptive strategy for determining the weights and biases of newly added neurons, enabling the network to expand in both width and depth without requiring additional training. Instead, all weights and biases are generated constructively, significantly enhancing the network’s approximation capabilities compared to conventional randomized neural network methods. In addition, a domain splitting strategy is introduced to handle the case of discontinuous solutions. Extensive numerical experiments are conducted to demonstrate the efficiency and accuracy of this innovative approach. Copyright © 2024, The Authors. All rights reserved.

关键词： Partial differential equations

Accurate calculation of bubble and droplet properties in diffuse-interface two-phase simulations

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Journal of computational physics 2025年 538卷

作者： Pranav J. Nathan Suhas S. Jain Flow Physics and Computational Science Lab George W. Woodruff School of Mechanical EngineeringGeorgia Institute of Technology Atlanta GA USA

In this paper, we address the challenge of accurately calculating droplet/bubble properties (e.g., volume, number) in diffuse-interface two-phase flow simulations. Currently, flood-fill algorithms can truncate a significant portion of the volume of droplets/bubbles contained within the diffuse interface region or artificially merge multiple droplets/bubbles. This error is also dependent on the volume fraction cutoff value, which is typically chosen to be 0.5 arbitrarily, in the flood-fill algorithms. We propose a simple volume-correction approach that incorporates an analytical approximation of the truncated volume to correct for the missing droplet/bubble volumes. This proposed method results in accurately recovering the dispersed phase volumes with minimal volume error over a wide range of volume fraction cutoff values, and hence, can also accurately recover the number of droplets/bubbles. This can be a valuable tool for accurate calculation of drop/bubble size distributions for analysis and for Eulerian-to-Lagrangian conversion of the dispersed phase in multi-scale modeling approaches.

关键词： Two-phase flow Flood fill Diffuse-interface method Drops Bubbles

multiRegionFoam – A Unified Multiphysics Framework for Multi-Region Coupled Continuum-Physical Problems

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arXiv 2023年

作者： Alkafri, Heba Habes, Constantin Fadeli, Mohammed Elwardi Hess, Steffen Beale, Steven B. Zhang, Shidong Jasak, Hrvoje Marschall, Holger Technische Universität Darmstadt Department of Mathematics Computational Multiphase Flow Darmstadt64287 Germany Jülich52428 Germany Queen’s University Department of Mechanical and Materials Engineering KingstonONK7L 3N6 Canada The Cavendish Laboratory Department of Physics University of Cambridge United Kingdom

This paper presents a unified framework, called multiRegionFoam, for solving multiphysics problems of the multi-region coupling type within OpenFOAM (FOAM-extend). It is intended to supersede the existing solver with the same name. The design of the new framework is modular, allowing users to assemble a multiphysics problem region-by-region and coupling conditions interface-by-interface. The present approach allows users to choose between deploying either monolithic or partitioned interface coupling for each individual transport equation. The formulation of boundary conditions is generalised in the sense that their implementation is based on the mathematical jump/transmission conditions in the most general form for tensors of any rank. The present contribution focuses on the underlying mathematical model for these types of multiphysics problems, as well as on the software design and resulting code structure that enable a flexible and modular approach. Finally, deployment for different multi-region coupling cases is demonstrated, including conjugate heat, multiphase flows and fuel-cells. Source code repository: https://***/hmarschall/multiregionfoam/MSC Codes 76-04, 76-10 © 2023, CC BY-SA.

关键词： Multiphysics

ABACUS: An Electronic Structure Analysis Package for the AI Era

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arXiv 2025年

作者： Zhou, Weiqing Zheng, Daye Liu, Qianrui Lu, Denghui Liu, Yu Lin, Peize Huang, Yike Peng, Xingliang Bao, Jie J. Cai, Chun Jin, Zuxin Wu, Jing Zhang, Haochong Jin, Gan Ji, Yuyang Shen, Zhenxiong Liu, Xiaohui Sun, Liang Cao, Yu Sun, Menglin Liu, Jianchuan Chen, Tao Liu, Renxi Li, Yuanbo Han, Haozhi Liang, Xinyuan Bao, Taoni Chen, Nuo Ren, Hongxu Zhang, Xiaoyang Liu, Zhaoqing Fu, Yiwei Liu, Maochang Li, Zhuoyuan Wen, Tongqi Tang, Zechen Xu, Yong Duan, Wenhui Wang, Xiaoyang Gu, Qiangqiang Dai, Fu-Zhi Zheng, Qijing Zhao, Jin Zhang, Yuzhi Ou, Qi Jiang, Hong Liu, Shi Xu, Ben Xu, Shenzhen Ren, Xinguo He, Lixin Zhang, Linfeng Chen, Mohan AI for Science Institute Beijing100080 China HEDPS CAPT School of Physics College of Engineering Peking University Beijing100871 China College of Engineering Peking University Beijing100871 China Institute of Artificial Intelligence Hefei Comprehensive National Science Center Hefei230026 China Key Laboratory of Quantum Information University of Science and Technology of China Hefei230026 China Supercomputing Center University of Science and Technology of China Anhui Hefei230026 China Institute of Physics Chinese Academy of Sciences Beijing100190 China School of Materials Science and Engineering Peking University Beijing100871 China School of Electrical Engineering and Electronic Information Xihua University Chengdu610039 China Academy for Advanced Interdisciplinary Studies Peking University Beijing100871 China College of Chemistry and Molecular Engineering Peking University Beijing100871 China International Research Center for Renewable Energy State Key Laboratory of Multiphase Flow Xi’an Jiaotong University Shaanxi Xi’an710049 China Suzhou Academy of Xi’an Jiaotong University Jiangsu Suzhou215123 China Center for Structural Materials Department of Mechanical Engineering The University of Hong Kong Hong Kong The University of Hong Kong Shenzhen China State Key Laboratory of Low Dimensional Quantum Physics Department of Physics Tsinghua University Beijing100084 China Frontier Science Center for Quantum Information Beijing China Saitama Wako351-0198 Japan Institute for Advanced Study Tsinghua University Beijing100084 China Laboratory of Computational Physics Institute of Applied Physics and Computational Mathematics Fenghao East Road 2 Beijing100094 China School of Artificial Intelligence and Data Science University of Science and Technology of China Hefei230026 China School of Materials Science and Engineering University of Science and Technology Beijing Beijing100083 China Department of Physics University of Science and

ABACUS (Atomic-orbital Based Ab-initio Computation at USTC) is an open-source software for first-principles electronic structure calculations and molecular dynamics simulations. It mainly features density functional theory (DFT) and is compatible with both plane-wave basis sets and numerical atomic orbital basis sets. ABACUS serves as a platform that facilitates the integration of various electronic structure methods, such as Kohn-Sham DFT, stochastic DFT, orbital-free DFT, and real-time time-dependent DFT, etc. In addition, with the aid of high-performance computing, ABACUS is designed to perform efficiently and provide massive amounts of first-principles data for generating general-purpose machine learning potentials, such as DPA models. Furthermore, ABACUS serves as an electronic structure platform that interfaces with several AI-assisted algorithms and packages, such as DeePKS-kit, DeePMD, DP-GEN, DeepH, DeePTB, etc. Copyright © 2025, The Authors. All rights reserved.

关键词： Stochastic systems

Impact of network heterogeneity on nonlinear electrokinetic transport in porous media

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arXiv 2019年

作者： Alizadeh, Shima Bazant, Martin Z. Mani, Ali Department of Mechanical Engineering Flow Physics and Computational Engineering Stanford University StanfordCA94305 United States Department of Chemical Engineering Massachusetts Institute of Technology CambridgeMA02139 United States Center for Turbulence Research Stanford University StanfordCA94305 United States

We present a numerical study of nonlinear electrokinetic transport in porous media, focusing on the role of heterogeneity in a porous microstructure on ion concentration polarization and over-limiting current. For simplicity, the porous medium is modeled as a network of long, thin charged cylindrical pores, each governed by one-dimensional effective transport equations. For weak surface conduction, when sufficiently large potential is applied, we demonstrate that electrokinetic transport in a porous network can be dominated by electroconvection via internally induced flow loops, which is not properly captured by existing homogenized models. We systematically vary the topology and "accessivity" of the pore network and compare with simulations of traditional homogenized parallel-pore (capillary-bundle) models, in order to reveal the effects of regular and hierarchical connectivity. Our computational framework sheds light on the complex physics of nonlinear electrokinetic phenomena in microstructures and may be used to design porous media for applications, such as water desalination and purification by shock electrodialysis. Copyright © 2019, The Authors. All rights reserved.

关键词： Porous materials

flow behaviors of shale oil in kerogen slit by molecular dynamics simulation

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Chemical engineering Journal 2022年 434卷

作者： Jie Liu Yongfei Yang Shuyu Sun Jun Yao Jianlong Kou Physical Science and Engineering Division (PSE) Computational Transport Phenomena Laboratory King Abdullah University of Science and Technology (KAUST) Thuwal 23955-6900 Saudi Arabia Key Laboratory of Unconventional Oil & Gas Development (China University of Petroleum (East China)) Ministry of Education Qingdao 266580 PR China Research Center of Multiphase Flow in Porous Media School of Petroleum Engineering China University of Petroleum (East China) Qingdao 266580 PR China Institute of Condensed Matter Physics Zhejiang Normal University Jinhua 321004 PR China

In the last decades, shale oil, mainly distributed in the nanopores of shale, has been considered as the representative of unconventional energy to alleviate the energy crisis. But the ideal pore models greatly overestimate the flowing capability of shale oil. To get more accurate and reasonable flow behavior, the multicomponent shale oil in the realistic kerogen channel is studied by using molecular dynamic simulation. Both density and velocity distributions that along and perpendicular to the flow direction are studied in kerogen channel, where the influence of branch chain of kerogen is also took into consideration. The heavy component tends to form the adsorbed layers on the kerogen wall, as a result of the extremely strong affinity between kerogen and hydrocarbons, and some asphaltene molecules in bulk phase form the cluster in middle of slit. On the flow direction, the velocity profile preforms the peristaltic behavior due to the effect of branch chain of kerogen, and the toluene and asphaltene components contribute it mostly. According to the heterogeneous characteristics of shale oil flow, we define the fictitious slip boundary, which corresponds to the boundary between bulk phase and adsorbed phase, to describe shale oil flow precisely. We also examine the effects of driving pressure gradient, temperature and pore size on the flow behaviors. The enhancements of driving force and temperature both facilitate shale oil flow, and the maximum velocity reaches the stable value within larger kerogen pores. The potential energy distribution and the interaction force contour verified the peristaltic flow behavior and the validity of fictitious slip boundary.

关键词： Shale oil Kerogen flow behavior Molecular simulation

Discontinuous galerkin method for predicting heat transfer in hypersonic environments 55

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Discontinuous galerkin method for predicting heat transfer i...

55th AIAA Aerospace Sciences Meeting

作者： Ching, Eric Lv, Yu Ihme, Matthias Flow Physics and Computational Engineering Department of Mechanical Engineering Stanford University StanfordCA94305 United States

ISBN: (纸本)9781624104473

This study is concerned with predicting surface heat transfer in steady hypersonic flows using high-order discontinuous Galerkin methods. A robust shock capturing method that uses smooth artificial viscosity for shock stabilization is developed. To minimize parametric dependence, an optimization method is formulated that results in the least amount of artificial viscosity necessary to sufficiently suppress nonlinear instabilities and achieve steady-state convergence. The performance is evaluated in hypersonic flows over a circular half-cylinder. Results show this methodology to be significantly less sensitive than conventional finite-volume techniques to mesh topology and inviscid flux function. © 2017, American Institute of Aeronautics and Astronautics. All Rights reserved.

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