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Fluids
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Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime
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Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime

A special issue of Fluids (ISSN 2311-5521).

Deadline for manuscript submissions: 28 February 2025 | Viewed by 10372

Special Issue Editor

Dr. Ehsan Roohi

E-Mail Website
Guest Editor
School of Aerospace Engineering, International Center for Applied Mechanics (ICAM), Xi’an Jiaotong University (XJTU), Xi'an 710049, China
Interests: rarefied gas dynamics; Direct Simulation Monte Carlo (DSMC); cavitating and two phase flows; micro and nano flows; microfluidics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

The physics of rarefied gas transport at micro and nano scales and at hypersonic regimes has attracted the attention of many researchers from multi-disciplinary fields. The detection of non-intuitive and unusual behaviors of gas flow at the micro and nano scales has assisted engineers in developing a diverse range of technologies, from lab-on-a-chip devices for medical diagnostics to water filtration systems using carbon nanotubes. Advances in kinetic theory and numerical methods to treat rarefied gas flows, such as direct simulation Monte Carlo (DSMC), Fokker–Planck, and other schemes, make the study of flow at hypersonic regimes and beyond less time-consuming and more accurate. 

This Special Issue aims to elucidate past developments, report the current knowledge, and illuminate the future of rarefied gas dynamics. As a leading researcher in the field, we would very much appreciate if you could contribute to this Special Issue by reporting your work on advancing our understanding of rarefied gas flows from micro–nano scales to hypersonic regimes.

Potential topics will include, but are not limited to:

  • Boltzmann and related equations;
  • Continuum-based simulation of micro and nano scale flows and at hypersonic regimes;
  • Extended hydrodynamics;
  • Fluid surface interactions including the Knudsen layer;
  • Direct simulation Monte Carlo (DSMC): Numerical advances and applications;
  • Molecular and continuum simulations at micro and nanoscale;
  • Experimental micro and nano flows and hypersonic regime;
  • Shale gases and porous media flows;
  • Gas kinetic theory;
  • Multiphase flow at micro and nano scale;
  • Theoretical, experimental, computational, and thermodynamic aspects of RGD;
  • Kinetic theory for gases and complex systems;
  • Non-equilibrium reacting flows;
  • Shock waves in rarefied flows;
  • Vacuum technology;
  • Plasma flows and processes;
  • Jets and plumes;
  • Gas–surface interactions
  • Machine learning and rarefied gas dynamics.

Dr. Ehsan Roohi
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Fluids is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 1800 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (5 papers)

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Research

15 pages, 4316 KiB  
Article
Numerical Analysis of Knudsen Number of Helium Flow Through Gas-Focused Liquid Sheet Micro-Nozzle
by Krištof Kovačič, Saša Bajt and Božidar Šarler
Fluids 2024, 9(12), 273; https://doi.org/10.3390/fluids9120273 - 22 Nov 2024
Viewed by 509
Abstract
This work aims to verify whether the continuum mechanics assumption holds for the numerical simulation of a typical sample delivery system in serial femtosecond crystallography (SFX). Knudsen numbers were calculated based on the numerical simulation results of helium flow through the gas-focused liquid [...] Read more.
This work aims to verify whether the continuum mechanics assumption holds for the numerical simulation of a typical sample delivery system in serial femtosecond crystallography (SFX). Knudsen numbers were calculated based on the numerical simulation results of helium flow through the gas-focused liquid sheet nozzle into the vacuum chamber, representing the upper limit of Knudsen number for such systems. The analysed flow is considered steady, compressible, and laminar. The numerical results are mesh-independent, with a Grid Convergence Index significantly lower than 1% for global and local analysis. This study is based on an improved definition of the numerical Knudsen number: a combination of the cell Knudsen number and the physical Knudsen number. In the analysis, no-slip boundary and low-pressure boundary slip conditions are compared. No significant differences are observed. This study justifies using computational fluid dynamics (CFD) analysis for SFX sample delivery systems based on the assumption of continuum mechanics. Full article
(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)
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26 pages, 881 KiB  
Article
Lattice Boltzmann Model for Rarefied Gaseous Mixture Flows in Three-Dimensional Porous Media Including Knudsen Diffusion
by Michel Ho, Jean-Michel Tucny, Sami Ammar, Sébastien Leclaire, Marcelo Reggio and Jean-Yves Trépanier
Fluids 2024, 9(10), 237; https://doi.org/10.3390/fluids9100237 - 9 Oct 2024
Viewed by 3147
Abstract
Numerical modeling of gas flows in rarefied regimes is crucial in understanding fluid behavior in microscale applications. Rarefied regimes are characterized by a decrease in molecular collisions, and they lead to unusual phenomena such as gas phase separation, which is not acknowledged in [...] Read more.
Numerical modeling of gas flows in rarefied regimes is crucial in understanding fluid behavior in microscale applications. Rarefied regimes are characterized by a decrease in molecular collisions, and they lead to unusual phenomena such as gas phase separation, which is not acknowledged in hydrodynamic equations. In this work, numerical investigation of miscible gaseous mixtures in the rarefied regime is performed using a modified lattice Boltzmann model. Slip boundary conditions are adapted to arbitrary geometries. A ray-tracing algorithm-based wall function is implemented to model the non-equilibrium effects in the transition flow regime. The molecular free flow defined by the Knudsen diffusion coefficient is integrated through an effective and asymmetrical binary diffusion coefficient. The numerical model is validated with mass flow measurements through microchannels of different cross-section shapes from the near-continuum to the transition regimes, and gas phase separation is studied within a staggered arrangement of spheres. The influence of porosity and mixture composition on the gas separation effect are analyzed. Numerical results highlight the increase in the degree of gas phase separation with the rarefaction rate and the molecular mass ratio. The various simulations also indicate that geometrical features in porous media have a greater impact on gaseous mixtures’ effective permeability at highly rarefied regimes. Finally, a permeability enhancement factor based on the lightest species of the gaseous mixture is derived. Full article
(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)
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21 pages, 4512 KiB  
Article
Numerical Study of Rarefied Gas Flow in Diverging Channels of Finite Length at Various Pressure Ratios
by Christos Tantos, Foteini Litovoli, Tim Teichmann, Ioannis Sarris and Christian Day
Fluids 2024, 9(3), 78; https://doi.org/10.3390/fluids9030078 - 19 Mar 2024
Viewed by 2003
Abstract
In the present work, the gas flows through diverging channels driven by small, moderate, and large pressure drops are studied, considering a wide range of the gas rarefaction from free molecular limit through transition flow regime up to early slip regime. The analysis [...] Read more.
In the present work, the gas flows through diverging channels driven by small, moderate, and large pressure drops are studied, considering a wide range of the gas rarefaction from free molecular limit through transition flow regime up to early slip regime. The analysis is performed using the Shakhov kinetic model, and applying the deterministic DVM method. The complete 4D flow problem is considered by including the upstream and downstream reservoirs. A strong effect of the channel geometry on the flow pattern is shown, with the distributions of the macroscopic quantities differing qualitatively and quantitatively from the straight channel flows. The mass flow rate data set from the complete solution is compared with the corresponding set obtained from the approximate kinetic methodology, which is based on the fully developed mass flow rate data available in the literature. In addition, the use of the end-effect approach significantly improves the applicability range of the approximate kinetic methodology. The influence of the wall temperature on the flow characteristics is also studied and is found to be strong in less-rarefied cases, with the mass flow rate in these cases being a decreasing function of the temperature wall. Overall, the present analysis is expected to be useful in the development and optimization of technological devices in vacuum and aerospace technologies. Full article
(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)
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17 pages, 1432 KiB  
Article
Transition to the Fluid Dynamic Limit: Mathematical Models and Simulation Results
by Hans Babovsky
Fluids 2024, 9(3), 72; https://doi.org/10.3390/fluids9030072 - 11 Mar 2024
Viewed by 1298
Abstract
Numerical simulations of standard situations in the transition region from gas kinetics to fluid dynamics at small Mach numbers indicate a clear dependence of the simulation results on the underlying kinetic model (here: nonlinear and linearized Boltzmann collision operator vs. BGK relaxation model). [...] Read more.
Numerical simulations of standard situations in the transition region from gas kinetics to fluid dynamics at small Mach numbers indicate a clear dependence of the simulation results on the underlying kinetic model (here: nonlinear and linearized Boltzmann collision operator vs. BGK relaxation model). We develop an improved mathematical framework (trace theory) to explain these differences. In particular we reveal certain deficiencies for the classical BKG system as well as for the standard Navier Stokes approach. Full article
(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)
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9 pages, 5089 KiB  
Article
Thermal Transpiration Flow: Molecular Dynamics Study from Dense to Dilute Gas
by Hiroki Yamaguchi and Gota Kikugawa
Fluids 2024, 9(1), 12; https://doi.org/10.3390/fluids9010012 - 30 Dec 2023
Viewed by 1724
Abstract
Thermal transpiration flow, a flow from cold to hot, driven by a temperature gradient along a wall under a high Knudsen number condition, was studied using the molecular dynamics method with a two-dimensional channel consisting of infinite parallel plates with nanoscale clearance based [...] Read more.
Thermal transpiration flow, a flow from cold to hot, driven by a temperature gradient along a wall under a high Knudsen number condition, was studied using the molecular dynamics method with a two-dimensional channel consisting of infinite parallel plates with nanoscale clearance based on our previous study. To accelerate the numerical analysis, a dense gas was employed in our previous study. In this study, the influence of the number density of gas was investigated by varying the height of the channel while keeping the number of molecules to achieve the flow ranging from dense to dilute gas while maintaining a constant Knudsen number. From the flow velocity profile compared to the number density profile, the thermal transpiration flow was observed for all number density conditions from dense to dilute gas. A similar flow structure was exhibited regardless of the number density. Thus, the numerical analysis in a dense gas condition is considered to be valid and useful for analyzing the thermal transpiration flow. Full article
(This article belongs to the Special Issue Rarefied Gas Flows: From Micro-Nano Scale to Hypersonic Regime)
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