Discrete Boltzmann multi-scale modeling of non-equilibrium multiphase flows

Gan, Yanbiao; Xu, Aiguo; Lai, Huilin; Li, Wei; Sun, Guanglan; Succi, Sauro

doi:10.48550/arxiv.2203.12458

Cited by 3 publications

(4 citation statements)

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“…13(b), τ has tripled but the peak value of (∇u : ∇u) 0.5 only decreases 1.62 times. Although the pre-factors of the first order of ∆ * m,n are proportional to τ [55], our result D * max ∼ τ h (0 < h < 1) because the model we used essentially considers not noly the first order TNE but also the second order TNE, and the second order one is always reversed to the first order one in the two-phase flow system.…”

Section: B Effects Of Surface Tension and Viscositymentioning

confidence: 67%

“…This process is accompanied by the release of potential energy, thus the average velocity of molecules in the bubble increases and gets the maximum at t = 5.4 (this instant is marked as t umax ). When t > t umax , the average velocity because its strength is about five times of ∆ * 2 [55]. According to the results of Ref.…”

Section: A Non-equilibrium Characteristics Of Bubble Coalescencementioning

confidence: 86%

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Thermodynamic non-equilibrium effects in bubble coalescence: A discrete Boltzmann study

Sun,

Gan,

et al. 2022

Preprint

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The Thermodynamic Non-Equilibrium (TNE) effects in the coalescing process of two initially static bubbles under thermal conditions are investigated by a Discrete Boltzmann Model (DBM).The spatial distributions of the typical none-quilibrium quantity, i.e., the Non-Organized Momentum Fluxes (NOMF) during evolutions are investigated in detail. The density-weighted statistical method is used to highlight the relationship between the TNE effects and the morphological or kinetics characteristics of bubble coalescence. It is found that the xx-component and yy-component of NOMF are anti-symmetrical; the xy-component changes from an anti-symmetric internal and external double quadrupole structure to an outer octupole structure during the coalescing process.More importantly, the evolution of the averaged xx-component of NOMF provides two characteristic instants, which divide the non-equilibrium process into three stages. The first instant corresponds to the moment when the mean coalescing speed gets the maximum and at this time the ratio of minor and major axes is about 1/2. The second instant corresponds to the moment when the ratio of minor and major axes gets 1 for the first time. It is interesting to find that the three quantities, TNE intensity, acceleration of coalescence and negative slope of boundary length, show a high degree of correlation and attain their maxima simultaneously. Surface tension and heat conduction accelerate the process of bubble coalescence while viscosity delays it. Both surface tension and viscosity enhance the global non-equilibrium intensity, whereas heat conduction restrains it. These TNE features and findings present some new insights into the kinetics of bubble coalescence.

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Section: B Effects Of Surface Tension and Viscositymentioning

confidence: 67%

Section: A Non-equilibrium Characteristics Of Bubble Coalescencementioning

confidence: 86%

Thermodynamic non-equilibrium effects in bubble coalescence: A discrete Boltzmann study

Sun,

Gan,

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

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“…Therefore, DBM is a further development of the statistical physics phase space description method in the framework of the discrete Boltzmann equation, which presents an intuitive geometric correspondence for the complex non-equilibrium behavior. DBM can surpass the traditional fluid modeling in terms of both depth and width of non-equilibrium behavior description [44][45][46][47][48].…”

Section: The Construction Of Dbmmentioning

confidence: 99%

Rayleigh–Taylor instability under multi-mode perturbation: Discrete Boltzmann modeling with tracers

Li¹,

Xu²,

Zhang³

et al. 2022

Commun. Theor. Phys.

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The two-dimensional Rayleigh-Taylor Instability (RTI) under multi-mode perturbation in compressible flow is probed via the Discrete Boltzmann Modeling (DBM) with tracers. The distribution of tracers provides clear boundaries between light and heavy fluids in the position space. Besides, the position-velocity phase space offers a new perspective for understanding the flow behavior of RTI with intuitive geometrical correspondence. The effects of viscosity, acceleration, compressibility, and Atwood number on the mixing of material and momentum and the mean non-equilibrium strength at the interfaces are investigated separately based on both the mixedness defined by the tracers and the non-equilibrium strength defined by the DBM. The mixedness increases with viscosity during early stage but decreases with viscosity at the later stage. Acceleration, compressibility, and Atwood number show enhancement effects on mixing based on different mechanisms. After the system relaxes from the initial state, the mean non-equilibrium strength at the interfaces presents an initially increasing and then declining trend, which is jointly determined by the interface length and the macroscopic physical quantity gradient. We conclude that the four factors investigated all significantly affect early evolution behavior of RTI system, such as the competition between interface length and macroscopic physical quantity gradient. The results contribute to the understanding of the multi-mode RTI evolutionary mechanism and the accompanied kinetic effects.

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“…34 Over the past decades, various kinetic methods have been developed to model and simulate the complex non-equilibrium flows over a wide range of Knudsen numbers. [35][36][37][38] In order to study aerodynamic problems covering various flow regimes, Li et al 4,[39][40][41][42][43] presented a unified computable modeling on the collision integral of the Boltzmann equation, in which the molecular collision relaxing parameter and the local equilibrium distribution function can be integrated with the macroscopic flow variables, the gas viscosity transport coefficient, the thermodynamic effect, the molecular power law, molecular models, and the flow state controlling parameter from various flow regimes and the gas-kinetic unified algorithm (GKUA) has been presented and used to simulate the gas flows from highly rarefied free-molecule flow to continuum flow regimes with the whole range of Knudsen numbers, specially to research the aerodynamic behaviors for the uncontrolled Tiangong-1 target spacecraft, the controlled Tiangong-2 space laboratory successively during the reentry and microscale flows in MEMS devices. In this working, the application of the GKUA in two-dimensional profile nozzles and axisymmetric nozzles will be specifically studied, and a unified gas kinetic expression form that can describe the flow of two-dimensional planar nozzles and axisymmetric nozzles will be established.…”

Section: Introductionmentioning

confidence: 99%

Gas‐kinetic unified algorithm for two‐dimensional planar and axisymmetric nozzle flows

Jiang

et al. 2023

Numerical Methods in Fluids

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SummaryFor high‐altitude nozzle or micronozzle flows and other gas flows in the slip or transition flow regime, how to solve it reliably has always been a difficult problem. In this paper, a unified gas kinetic expression is presented to describe the two‐dimensional planar and the axisymmetric nozzle flows, and the computable modeling of the Boltzmann equation is developed at the first time for the nozzle flows by introducing the gas molecular collision relaxing parameter and the local equilibrium distribution function integrated in the unified expression with the flow state controlling parameter, including the macroscopic flow variables, the gas viscosity transport coefficient, the thermodynamic effect, the molecular power law, and molecular models, covering a full spectrum of flow regimes. The boundary conditions involved in the nozzle flow have been mathematically expressed at the level of the gas molecular velocity distribution function, and the model equations have been solved uniformly by the gas‐kinetic unified algorithm (GKUA) for rarefied transition to continuum flows. The presented simulated results from the test cases show promising of simulating gas flow from transitional flow to continuum flow in the same flow domain, especially for those flow involving low‐speed gas flow in rarefied regime, which is otherwise practically difficult using direct simulation Monte Carlo (DSMC).

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Discrete Boltzmann multi-scale modeling of non-equilibrium multiphase flows

Cited by 3 publications

References 0 publications

Thermodynamic non-equilibrium effects in bubble coalescence: A discrete Boltzmann study

Thermodynamic non-equilibrium effects in bubble coalescence: A discrete Boltzmann study

Rayleigh–Taylor instability under multi-mode perturbation: Discrete Boltzmann modeling with tracers

Gas‐kinetic unified algorithm for two‐dimensional planar and axisymmetric nozzle flows

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