Abstract We describe the implementation of a computational fluid dynamics solver for simulation high‐speed flows. It comprises finite volume (FV) discretization using semi‐discrete, non‐staggered central schemes colocated variables prescribed on mesh polyhedral cells that have an arbitrary number faces. in detail, explaining choice whose face interpolation is limited, limiter, and method limiting vector field independent coordinate system. The solution momentum energy transport Navier–Stokes...

dsmcFoam+ is a direct simulation Monte Carlo (DSMC) solver for rarefied gas dynamics, implemented within the OpenFOAM software framework, and parallelised with MPI. It open-source released under GNU General Public License in publicly available repository that includes detailed documentation tutorial DSMC flow cases. This release of code many features not found standard dsmcFoam, such as molecular vibrational electronic energy modes, chemical reactions, subsonic pressure boundary conditions....

Maxwell's famous slip boundary condition is often misapplied in current rarefied gas flow calculations (e.g., hypersonics, microfluidics). For simulations of flows over curved or moving surfaces, this means crucial physics can be lost. We give examples such cases. also propose a higher-order based on general equation and the constitutive relations derived by Burnett. Unlike many other conditions these are applicable to any form surface geometry. It shown that "Maxwell-Burnett" reasonable...

An open-source implementation of chemistry modeling for the direct simulation Monte Carlo method is presented. Following recent work Bird ( G. A. , " The Q-K Model Gas Phase Chemical Reaction Rates ," Physics Fluids Vol. 23 No. 10 2011 Paper 106101 ), an approach known as quantum-kinetic has been adopted to describe chemical reactions in a five-species air model using procedures based on microscopic gas information. technique implemented within framework dsmcFoam code, derivative...

Abstract Based on the fast spectral approximation to Boltzmann collision operator, we present an accurate and efficient deterministic numerical method for solving equation. First, linearized equation is solved Poiseuille thermal creep flows, where influence of different molecular models mass heat flow rates assessed, Onsager–Casimir relation at microscopic level large Knudsen numbers demonstrated. Recent experimental measurements along a rectangular tube with aspect ratio are compared...

We employ molecular dynamics simulations to study the wetting and evaporation of salt-water nanodroplets on platinum surfaces. Our results show that contact angle droplets increases with salt concentration. To verify this, a second simulation system thin film surface is used calculate various tensions. find both solid-liquid liquid-vapor tensions increase concentration as result these cause an in angle. However, rate decreases increases, due hydration ions. When water molecules have all...

The high water flow rates observed in carbon nanotubes (CNTs) have previously been attributed to the unfavorable energetic interaction between liquid and graphitic walls of CNTs. This paper reports molecular dynamics simulations carbon, boron nitride, silicon carbide that show effect solid-liquid interactions on fluid flow. Alongside an analytical model, these results enhancement depends tube's geometric characteristics interactions.

Abstract A kinetic model of the Boltzmann equation for non-vibrating polyatomic gases is proposed, based on Rykov diatomic gases. We adopt two velocity distribution functions (VDFs) to describe system state; inelastic collisions are same as in model, but elastic modelled by collision operator (BCO) monatomic gases, so that overall reduces limit no translational–rotational energy exchange. The free parameters determined comparing transport coefficients, obtained a Chapman–Enskog expansion,...

The classical notion of the coalescence two droplets same radius R is that surface tension drives an initially singular flow. In this Letter we show, using molecular dynamics simulations coalescing water nanodroplets, after single or multiple bridges form due to presence thermal capillary waves, bridge growth commences in a regime. Here, expand linearly time much faster than viscous-capillary speed collective jumps near fronts. Transition hydrodynamic regime only occurs once exceeds length...

Water purification membranes comprising aligned, dense arrays of carbon nanotubes (CNTs) have been investigated for more than 10 years. transport 2–5 orders magnitude greater Hagen-Poiseuille predictions has observed in CNTs diameters 0.8–10 nm a small number experiments. While the measured flow rates different experiments substantially disagree with each other, there is clear opportunity these to impact filtration technologies. We propose multiscale computational method that combines...

The Knudsen layer is an important rarefaction phenomenon in gas flows and around microdevices. Its accurate efficient modeling of critical importance the design such systems predicting their performance. In this paper we investigate potential that higher-order continuum equations may have to model layer, compare predictions high-accuracy DSMC (direct simulation Monte Carlo) data, as well a standard result from kinetic theory. We find that, for benchmark case, most common equation sets...

In hypersonic aerodynamics and microflow device design, the momentum energy fluxes to solid surfaces are often of critical importance. However, these depend on characteristics Knudsen layer - region local non-equilibrium existing up one or two molecular mean free paths from wall in any gas flow near a surface. While has been investigated extensively using kinetic theory, ability capture it within continuum-fluid formulation (in conjunction with slip boundary conditions) suitable for current...

This paper makes two new propositions regarding the modelling of rarefied (non-equilibrium) isothermal gas flows at microscale. The first is a test case for benchmarking high-order, or extended, hydrodynamic models these flows. standing time-varying shear-wave problem does not require boundary conditions to be specified solid surface, so useful assessing whether fluid can capture rarefaction effects in bulk flow. We assess number different proposed extended models, and we find R13 equations...

Brenner has recently proposed modifications to the Navier-Stokes equations that are based on theoretical arguments but supported only by experiments having a fairly limited range. These relate diffusion of fluid volume would be significant for flows with high density gradients. So viscous structure shock waves in gases should provide an excellent test case this new model. In paper we detail problem and propose exponents gas viscosity-temperature relation empirical viscosity data is...

We propose a power-law based effective mean free path (MFP) model so that the Navier-Stokes-Fourier equations can be employed for transition-regime flows typical of gas micro/nanodevices. The MFP is derived system with planar wall confinement by taking into account boundary limiting effects on molecular paths. Our validated against dynamics simulation data and compared other theoretical models. As transport properties related to through kinetic theory, constitutive relations are then...

We present the results of investigations into distribution molecular free paths in rarefied gases using dynamics simulations. Our tests on a range different gas densities and confinements (unbounded, single bounding wall parallel walls) indicate that molecules perform Lévy-type flights, irrespective presence wall. The most closely follow power-law distribution. Simulations confined by planar surfaces local mean path varies sharply close to solid surface. These may yield new insight diffusive...

The properties of water confined inside nanotubes are considerable scientific and technological interest. We use molecular dynamics to investigate the structure average orientation flowing within a carbon nanotube. find that exhibits biaxial paranematic liquid crystal ordering both nanotube close its ends. This preferred is enhanced when an axial electric field applied, affecting flow rate through A spatially patterned can minimize entrance effects significantly increase rate.

Although the modified Young’s equation is frequently applied to evaluate line tension of droplets, debate concerning value and even sign ongoing. The reason for this that defined in not a pure but an apparent tension, which includes effects Tolman length stiffness coefficients. In paper, we employ molecular dynamics (MD) simulate three-dimensional water nanodroplets on platinum surfaces determine their tensions by applying linear fit relation cosine contact angle curvature line. position...