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Rarefied isothermal gaseous flow through long diverging micro and nanochannels is investigated in this paper using the two-relaxation-time (TRT) lattice Boltzmann method (LBM). The simulations are performed over a wide range of Knudsen number, pressure ratio, and divergence angle. The Bounce-Back Specular Reflection (BSR) slip boundary condition is applied and is connected to the second-order slip boundary condition coefficients by means of the antisymmetric relaxation time and the bounce-back portion parameter. The effects of the slip coefficients on the wall and centerline Mach numbers, as well as the mass flow rates, are investigated. The numerical results are validated with those of the direct simulation Monte Carlo (DSMC) reported in the literature. The results show that the local pressure distributions are almost independent of the slip coefficients with excellent agreements with DSMC over a wide range of the divergence angle. Our results demonstrate that there is a specific divergence angle at each pressure ratio where the local unbounded Knudsen and, as a result, Mach numbers remain constant along the channel. This observation is almost independent of the slip coefficients, and the underlying reason is that the pressure drop is compensated by an increase in the channel area. [ABSTRACT FROM AUTHOR]

Abstract A hybrid solver dynamically coupling the kinetic solution computed in local rarefied areas and the Navier–Stokes solution in the rest of the flow is used for the investigation of heat transfer in microchannels with rough wall surfaces. Roughness is modeled as a series of triangular obstructions with a relative roughness height from 0 up to 5% of the channel height. A nearly incompressible gas flow (low Mach number) for a range of Knudsen numbers from 0.01 up to 0.1 is considered. The competition between roughness, rarefaction and heat transfer effects is discussed in terms of average Nusselt and Poiseuille numbers and mass flow rate. The discrepancy between the full Navier–Stokes and hybrid solutions is analyzed, assessing the range of applicability of the first order slip boundary condition for rough geometries in the presence of heat transfer. Highlights • Hybrid solver dynamically coupling kinetic and Navier–Stokes solutions is used. • Roughness is modeled as a series of triangular obstructions. • A nearly incompressible gas flow for a range of Knudsen numbers is considered. • The competition between roughness, rarefaction and heat transfer effects is discussed. • Applicability of the slip condition for rough geometries is assessed. [ABSTRACT FROM AUTHOR]

The heat and mass transfer in a rarefied gas between its two parallel condensed phases is considered on the basis of linearized and non-linear S-model kinetic equations. The profiles of the macroscopic parameters in the gap between gas-liquid interfaces are obtained for several Knudsen numbers and for the cases of complete and non-complete evaporation and condensation. The linearized Navier–Stokes equations and energy equation, subjected to the temperature and pressure jump boundary conditions, are solved analytically and the expressions for the macroscopic parameters are obtained. The comparison of three approaches allowed us to establish the limit of the application of the linearized approaches in term of the saturation temperature ratio between the condensed phases. [ABSTRACT FROM AUTHOR]

CNT (Carbon nanotube)-based fluidic systems hold a great potential for emerging medical applications such as drug delivery for cancer therapy. CNTs can be used to deliver anticancer drugs into a target site under a magnetic field guidance. One of the critical issues in designing such systems is how to avoid the vibration induced by the fluid flow, which is undesirable and may even promote the structural instability. The main objective of the present research is to develop a fluid structure interaction (FSI) model to investigate the flutter instability of a cantilevered CNT induced by a magnetic fluid flow under a longitudinal magnetic field. The CNT is assumed to be embedded in a viscoelastic matrix to consider the effect of biological medium around it. To obtain a dynamical model for the system, the Navier–Stokes theory of magnetic-fluid flow is coupled to the Euler–Bernoulli beam model for CNT. The small size effects of the magnetic fluid and CNT are considered through the small scale parameters including Knudsen number ( Kn ) and the nonlocal parameter. Then, the extended Galerkin's method is applied to solve the FSI governing equations, and to derive the stability diagrams of the system. Results show how the magnetic properties of the fluid flow have an effect on improving the stability of the cantilevered CNT by increasing the flutter velocity. [ABSTRACT FROM AUTHOR]

Large eddy simulations (LES) of a lattice Boltzmann magnetohydrodynamic (LB-MHD) model are performed for the unstable magnetized Kelvin–Helmholtz jet instability. This algorithm is an extension of Ansumali et al. [1] to MHD in which one performs first an expansion in the filter width on the kinetic equations followed by the usual low Knudsen number expansion. These two perturbation operations do not commute. Closure is achieved by invoking the physical constraint that subgrid effects occur at transport time scales. The simulations are in very good agreement with direct numerical simulations. [ABSTRACT FROM AUTHOR]

The head-on collision of two droplets near the critical point is investigated based on the Boltzmann-BGK equation. Gauss–Hermite quadratures with different degree of precision are used to solve the kinetic equation, so that the solutions truncated at the Navier–Stokes order and non-continuum (i.e., rarefied fluid dynamics) solutions can be compared. When the kinetic equation is solved with adequate accuracy, prominent variations of the vertical velocity (the collision is in the horizontal direction), the viscous stress components, and droplet morphology are observed during the formation of liquid bridge, which demonstrates the importance of the rarefaction effects and the failure of the Navier–Stokes equation. The rarefaction effects change the topology of streamlines near the droplet surface, suppress the high-magnitude vorticity concentration inside the interdroplet region, and promote the vorticity diffusion around outer droplet surface. Two physical mechanisms responsible for the local energy conversion between the free and kinetic energies are identified, namely, the total pressure-dilatation coupling effect and the interaction between the density gradient and strain rate tensor. An energy conversion analysis is performed to show that the rarefaction effects can enhance the conversion from free energy to kinetic energy and facilitate the discharge of the gas interval along the vertical direction, thereby boosting droplet coalescence. Furthermore, the magnitude and the spatial oscillation frequency of the Lamb vector divergence inside the gas interval are shown to be suppressed by the rarefaction effects. It is found that the dynamic process in the gas interval is closely associated with the interaction between the adjacent positive and negative regions of the Lamb vector divergence. • Rarefaction effects in head-on binary droplet collision are studied based on the BGK-Boltzmann equation. • Rarefaction effects on hydrodynamic quantities and droplet morphology are demonstrated. • Physical insights are provided from the energy conversion analysis. • Features of Lamb vector divergence in the gas film are highlighted. [ABSTRACT FROM AUTHOR]

Fast ion transport and the resulting fusion yield reduction are computed at a gas-metal interface. The extent of fusion yield reduction is observed to depend sensitively on the charge state of the surrounding pusher material and the width of the atomically mixed region. These sensitivities suggest that idealized boundary conditions often implemented at the gas-pusher interface for the purpose of estimating fast ion loss will likely overestimate fusion reactivity reduction in several important limits. In addition, the impact of a spatially complex material interface is investigated by considering a collection of droplets of the pusher material immersed in a DT plasma. It is found that for small Knudsen numbers, the extent of fusion yield reduction scales with the surface area of the material interface. As the Knudsen number is increased, however, the simple surface area scaling is broken, suggesting that hydrodynamic mix has a nontrivial impact on the extent of fast ion losses. [ABSTRACT FROM AUTHOR]

The behavior of fluid-dynamic (or macroscopic) quantities of rarefied gases is studied, with a special interest in its non-analytic feature near boundaries. It is shown that their gradients normal to the boundary diverge even if the boundary is smooth, irrespective of the value of the (nonzero) Knudsen number. The boundary geometry determines the diverging rate. On a planar or concave boundary, the logarithmic divergence $$\ln s$$ should be observed, where s is the normal distance from the boundary. In other cases, the diverging rate is enhanced to be the inverse-power $$s^{-1/n}$$ , where $$n({\ge }2)$$ is the degree of the dominant terms of the polynomial which locally represents the boundary. Some numerical demonstrations are given as well. [ABSTRACT FROM AUTHOR]

The rarefied gas flow caused by a pressure drop in a planar microchannel of finite length is analysed numerically to investigate the effect of surface roughness on thermal and hydrodynamic flow characteristics. The kinetic approach based on the nonlinear S-model of the Boltzmann kinetic equation coupled with the Maxwell’s diffuse gas-surface interaction model imposed at the wall is used. An implicit scheme for the solution of the S-model kinetic equation is applied and the algorithm has been optimised for the use of massive parallelization in the velocity space. A surface roughness is configured with series of triangular, semicircular, trapezoidal and rectangular obstructions. A competition between rarefaction and effects of roughness geometry is estimated by varying a rarefaction regime of flow from continuum up to free–molecular regime. The results indicate that the global flow performances in terms of the Poiseuille number, mass and thermal energy flow rates are affected by the wall roughness geometry when compared to the flow performances for a smooth channel. The triangular roughness produces the smallest impact on a gas flow, while the rectangular roughness the largest one. Rarefaction plays a significant role enhancing the effect of the surface roughness. In the continuum flow regime the roughness elements induce strong recirculation and flow separation regions. Moreover, the weakly rarefied flow strongly depends on the shape and the spacing of roughness elements. On the other hand, for the highly rarefied flow the global parameters are almost independent of the shape of elements. The increase in the spacing of roughness elements results in the reduction of the Poiseuille number and an enhancement of mass and thermal energy flow rates for all shapes of roughness elements. [ABSTRACT FROM AUTHOR]

A novel model and a new numerical method are presented for the transport of solid particles in rarefied flows. The model is based on a Vlasov type equation where the particles are represented by a distribution function. The rarefied flow is described by a BGK or ES-BGK approach. An accurate method is proposed to solve the particle transport equation in a fully Eulerian framework. Validations in 2D with respect to analytical solutions and a Lagrangian method are presented. The numerical model is then used to explain a peculiar particle dynamics observed in satellite thrusters. [ABSTRACT FROM AUTHOR]

Various versions of the regularized 13-moment system (R13) are applied to the problem of the shock wave structure in a monatomic Maxwell gas for Mach numbers up to M = 10. Numerical solutions are compared to direct simulation Monte Carlo results computed by the SMILE++ software system, in order to identify applicability and limitations of the variants. Over time, several versions of the R13 equations were presented, which differ in non-linear contributions for high-order moments but agree in asymptotic expansion to the third order in the Knudsen number. All variants describe typical subsonic microflows well, for which the non-linear contributions only play a minor role. The challenge of the present study is to determine the real boundaries of applicability of each variant of the moment equations as applied to non-equilibrium supersonic flows, depending on the Mach number and local Knudsen number. [ABSTRACT FROM AUTHOR]

The goal of the present paper is to construct a relativistic extended thermodynamics (ET) theory of rarefied polyatomic gases. This is achieved by adopting the closure procedure for the 14 generalized moments of a distribution function that, as in the classical case, depends on an additional continuous variable representing the energy of the internal modes of a molecule. This permits the theory to take into account the energy exchange between translational modes and internal modes of a molecule in binary collisions. The theory includes the ET theory of monatomic gases as a singular limit and converges to the corresponding ET theory of polyatomic gases in the classical limit. In contrast to a monatomic gas in which the order of magnitude of the dynamical pressure is O ( 1 / c 2 ) , the dynamical pressure in a polyatomic gas is not small due to the internal motion of molecules as is the case in the classical limit. Therefore the present theory might result particularly useful in cosmology to describe some aspects of the post-recombination era. [ABSTRACT FROM AUTHOR]

HyPlane is the Italian aerospaceplane proposal targeting, at the same time, both the space tourism and point-to-point intercontinental hypersonic flights. Unlike other aerospaceplane projects, relying on boosters or mother airplanes that bring the vehicle to high altitude, HyPlane will take off and land horizontally from common runways. According to the current project, HyPlane will fly sub-orbital trajectories under high-supersonic/low-hypersonic continuum flow regimes. It can go beyond the von Karman line at 100 km altitude for a short time, then starting the descending leg of the trajectory. Its aerodynamic behavior up to 70 km have already been studied and the results published in previous works. In the present paper some aspects of the aerodynamic behavior of HyPlane have been analyzed at 80, 90 and 100 km. Computer tests, calculating the aerodynamic parameters, have been carried out by a Direct Simulation Monte Carlo code. The effects of the Knudsen, Mach and Reynolds numbers have been evaluated in clean configuration. The effects of the aerodynamic surfaces on the rolling, pitching and yawing moments, and therefore on the capability to control attitude, have been analyzed at 100 km altitude. The aerodynamic behavior has been compared also with that of another aerospaceplane at 100 km both in clean and flapped configuration. [ABSTRACT FROM AUTHOR]

In the present study, we investigate flow past a rotating cylinder over a wide range of flow rarefaction from the early slip through to the free-molecular regime using the direct simulation Monte Carlo method. We focus specifically on high-speed flow conditions and consider a wide range of Mach numbers near the high subsonic, transonic, and supersonic regimes. Various flow parameters such as the coefficients of lift and drag as well as the coefficients of pressure, skin friction, and wall heat transfer have been investigated as a function of both the Mach number and the Knudsen number to gain insight into the flow physics in the different regimes. The flow characteristics in the transonic regime have been found to be substantially different from those in the supersonic regime. In particular, an inverse Magnus effect involving a change in the direction of the lift force occurs in the supersonic regime. In contrast, subsonic flows in the early slip-flow regime experience the conventional direction for the Magnus lift force. This paper demonstrates that there is a subtle interplay between the Mach number and Knudsen number for the occurrence of the inverse Magnus effect. [ABSTRACT FROM AUTHOR]

Synthesis and performance evaluation of vertically aligned carbon nanotube membranes functionalized with different amine groups in order to separate H 2 S from binary mixtures of H 2 S/CH 4 were experimentally studied. For increasing the performance of the membrane, it was functionalized with butylamine, sec-butylamine, dodecylamine and octadecylamine. The effect of using linear amine groups with different carbon chain length and branched amine on increase of H 2 S permeability and selectivity of membrane was studied. The results showed that using linear amine with shorter carbon chain length is preferred to other amine groups, and the membrane functionalized with butylamine has the maximum selectivity and permeation values for the H 2 S. These values are reported to be 2.98 and 2.3 times those of obtained for the membrane with no functional group. The results also reveal that diffusivity of a N 2 single gas is 3.22 and 1.72 times of Knudsen’s diffusion before and after functionalization, respectively. [ABSTRACT FROM AUTHOR]

An ionized flow around the RAM C-II space vehicle is studied by the direct simulation Monte Carlo method in the range of altitudes of 73 to 81 km. It is shown that the predicted value of the plasma density in the shock layer essentially depends on the approach to simulation of high-temperature nonequilibrium dissociation. Good agreement of the results of numerical simulation with flight experiment data is obtained. [ABSTRACT FROM AUTHOR]

An improved hybrid particle simulation method (IHPSM) intended for hypersonic flows including various Knudsen number regimes is developed. In this approach, two different types of particle simulation methods, the direct simulation Monte Carlo (DSMC) method and the DSMC-based equilibrium particle simulation method (EPSM), are adopted to simulate the particle movement and collision in non-equilibrium regions and equilibrium regions respectively. We first present the design of equilibrium breakdown parameters to classify the cells into two different simulation regions. Then based on the information of the collision frequency and the maximum particle velocity in the cell, we further propose and employ a novel adaptive local time step method to increase the simulation efficiency. Finally, we verify the developed hybrid particle scheme through two representative test cases involving the hypersonic flows over a hollow cylinder-flare and a sphere. The IHPSM results show excellent agreement on flow field and surface properties with those obtained from the literature. Notably, the IHPSM method is able to decrease the simulation expense by about 55% compared with DSMC in the sphere test. [ABSTRACT FROM AUTHOR]

The Japan Aerospace Exploration Agency (JAXA) recently proposed a landing mission to Mars. To improve the feasibility of the mission, rarefied aerodynamics need to be accurately estimated for a precise determination of its flight path and landing site. This work has investigated rarefied hypersonic aerodynamics experimentally and numerically. A rarefied aerodynamic measurement scheme has been developed by using pendulous models in a hypersonic rarefied wind tunnel at JAXA, and the results have been compared with direct simulation Monte Carlo computations. Consequently, numerically predicted aerodynamic coefficients are consistent with the measured values. [ABSTRACT FROM AUTHOR]

In this paper we consider the extension of the method developed in Dimarco and Loubère (2013) [22,23] with the aim of facing the numerical resolution of multi-scale problems arising in rarefied gas dynamics. The scope of this work is to consider situations in which the whole domain does not demand the use of a kinetic model everywhere. This is the case of many realistic applications: some regions of the computational domain require a microscopic description, given by a kinetic model while the rest of the domain can be described by a coarser model of fluid type. Our aim is to show how the kinetic scheme developed in the pre-cited articles is perfectly suited for building domain decomposition strategies which make the method more attractive with respect to classical numerical techniques for kinetic equations and multi-scale realistic problems. Several numerical evidences are provided in this work in the two dimensional and three dimensional settings to assess the efficiency of the domain decomposition scheme. [ABSTRACT FROM AUTHOR]

Non-equilibrium rarefied flows are frequently encountered in a wide range of applications, including atmospheric re-entry vehicles, vacuum technology, and microscale devices. Rarefied flows at the microscale can be effectively modeled using the ellipsoidal statistical Bhatnagar–Gross–Krook (ESBGK) form of the Boltzmann kinetic equation. Numerical solutions of these equations are often based on the finite volume method (FVM) in physical space and the discrete ordinates method in velocity space. However, existing solvers use a sequential solution procedure wherein the velocity distribution functions are implicitly coupled in physical space, but are solved sequentially in velocity space. This leads to explicit coupling of the distribution function values in velocity space and slows down convergence in systems with low Knudsen numbers. Furthermore, this also makes it difficult to solve multiscale problems or problems in which there is a large range of Knudsen numbers. In this paper, we extend the coupled ordinates method (COMET), previously developed to study participating radiative heat transfer, to solve the ESBGK equations. In this method, at each cell in the physical domain, distribution function values for all velocity ordinates are solved simultaneously. This coupled solution is used as a relaxation sweep in a geometric multigrid method in the spatial domain. Enhancements to COMET to account for the non-linearity of the ESBGK equations, as well as the coupled implementation of boundary conditions, are presented. The methodology works well with arbitrary convex polyhedral meshes, and is shown to give significantly faster solutions than the conventional sequential solution procedure. Acceleration factors of 5–9 are obtained for low to moderate Knudsen numbers on single processor platforms. [ABSTRACT FROM AUTHOR]

A porous medium transport model with a distributed sublimation front is developed for low pressure freeze drying of beef by radiant surface heating and volumetric microwave heating. The model incorporates the importance of Knudsen flow in porous materials during low pressure freeze drying. This effort is part of fundamental physics-based framework building for simulating food and biomaterial processes involving rapid evaporation/sublimation. Temperature, pressure and ice saturation histories were computed. Drying rates and spatial temperature profiles showed excellent agreement with literature experimental data. Sublimation front width, a novel result, is seen to increase as ice saturation decreases, justifying the importance of this distributed sublimation formulation in contrast with the sharp sublimation front commonly employed in literature. The insulation effect of the gas fraction in the pores is observed by the slow movement of the sublimation front in 'thick' samples. Effects of porosity, initial ice saturation and microwave heating are illustrated. [ABSTRACT FROM AUTHOR]

The presented study is based on the idea of the activation of a gas-precursor high velocity flow by hot wire. The wire forms the channel for flow before expansion to substrate. The construction allows change of the specific flow rate, velocity, composition and temperature of a gas mixture by studying the film synthesis in conditions from free molecular to continuum flow at velocities from hundreds to thousands of m/s. At a high pressure, the film has typical and unusual hexagonal incorporations for diamond tetragonal particles. Raman spectrum with the pronounced diamond peak is typical for diamond-like film. X-ray diffraction points in the presence of lonsdaleite. Conditions of deposition were simulated by Monte Carlo method. Collisions with hot surfaces and chemical transformations were taken into consideration as well. [ABSTRACT FROM AUTHOR]

Analytical methods and techniques are required for design and analysis of low clearance gas-hearings that account for the combined influence of sut face roughness and Knudsen number. Analytical methods for the lubrication equation are currently available for bearings that are either high wave number-limited or high bearing number-limited. There are few useful analytical methods in the range between these limiting extremes that account for the combined effect of roughness and rarefaction. That is the focus of this paper as it extends the work reported by White (2013, "Surface Roughness Effects in the Region Between High Wave Number and High Bearing Number-Limited Lubricant Flows," ASME J. Tribol., 135(4), p. 041706) to include rarefaction effects. Results of an analytical study will be reported that investigates a wedge bearing geometry using perturbation methods and multiple-scale analysis over a wide range of Knudsen numbers for roughness on moving and stationary surfaces. The solution technique developed allows nonlinear aspects of the lubrication equation to be retained in the analysis. Solutions will be presented graphically and discussed. Results indicate that most of the bearing sensitivity to Knudsen number can be accounted for by a modified form of the bearing number [ABSTRACT FROM AUTHOR]

In this study, rarefied supersonic and subsonic gas flow around a NACA 0012 airfoil is simulated using both continuum and particle approaches. Navier-Stokes equations subject to the first order slip/jump boundary conditions are solved under the framework of OpenFOAM package. The DSMC solver of the package, i.e., dsmcFoam, has been improved to include a newly presented "simplified Bernoulli trial (SBT)" scheme for inter-molecular collision modeling. The use of SBT collision model permits to obtain accurate results using a much lower number of simulator particles. We considered flow at different angles of attacks and Knudsen numbers at both the subsonic and supersonic regimes. The computed density and surface pressure distributions are compared with the experimental and numerical data and suitable accuracy was observed. We investigate variations of the lift and drag coefficients with the Knudsen number and angle of attack. At low Kn number in supersonic regime, our results for lift coefficient agree well with the linearized theory; however, the deviation starts as soon as the angle of attack goes beyond 15 ° or shock wave forms above the airfoil. Along with this, we have observed that drag coefficient increases with the Kn number increasing. We also investigated the effect of Kn number on the leading edge shock position and structure, drag polar ( C L / C D ) , and slip velocity over the airfoil. [ABSTRACT FROM AUTHOR]

A thermal lattice Boltzmann method (TLBM) is presented for the analysis of fluid flow and heat transfer in two-dimensional channels with non-continuum effects. The relaxation times ( τ f , τ g ) are linked to the Knudsen number which accounts for the rarefaction that can be present at micro geometries or at low density conditions. The TLBM used here employs inlet/outlet boundary conditions to generate a forced convection problem where the calculation of equilibrium distributions at the wall surfaces are modified to incorporate the velocity slip and temperature jump conditions. Numerical simulations are obtained for thermal micro-Couette and thermal micro-Poiseuille channel flows and the effect of the Knudsen number on the velocity and temperature profile is investigated. [ABSTRACT FROM AUTHOR]

Time-dependent flows of single gases and binary gas mixtures with various molar fractions from a chamber through a short tube into vacuum are examined by simulations and experiments. The main goal is the comparison of the flow behaviour between pure gases and binary mixtures including the investigation of the gas separation effect. The simulations are based on an explicit hybrid scheme, coupling at each time step the tube flow rate estimated from a database accordingly constructed via a DSMC solver to the gas pressure in the chamber obtained by a mass conservation equation. Computational results describing the expansion process in terms of the temporal evolution of pressure in the chamber as well as of the total and species flow rates through the tube are reported. Comparison between computational and the corresponding deduced experimental pressures deduces a difference of about 10% which may be explained by accumulation of uncertainties in the time sequence. The binary gas mixture pressure evolution curves are always bounded by the corresponding ones of the components of the mixture flowing as single gases and the tube conductance varies in the opposite direction to that of the weighted mean of the component molar masses. Gas separation is monotonically increased as we move from the viscous towards the free molecular regime, while the rate with which gas separation is increased has a maximum in the transition regime. The equivalent single gas approach provides a reasonable estimate provided that the molar fraction of the light gas and the ratio of heavy to light molar mass are not too high. [ABSTRACT FROM AUTHOR]

Rarefied thermally-induced flows generate Knudsen thermal force on structures immersed in a gas and are significant for vacuum microbalances as well as for microsystem sensors and actuators. We study experimentally and numerically the influence of transverse thermal gradients on the Knudsen thermal force. A Peltier device provided the thermal gradient in a beam located in close proximity of a large reaction plate, whose displacement has been sensed using a torsional balance. The pressure in the vacuum chamber varied between 1 and 100 Pa giving a range of Knudsen numbers from the slip to nearly free molecular regimes, based on the gap between the beam and the movable plate. Switching polarity of the Peltier heater produces reversal of the Knudsen thermal force, from repulsive to attractive. The numerical solution of Ellipsoidal Statistical Bhatnagar–Gross–Krook (ESBGK) kinetic model of the Boltzmann equation agrees well with experimental data. The obtained non-dimensional Knudsen force coefficient, dependent on the Knudsen number, temperature ratio and the gap height to beam width aspect ratio, quantifies the magnitude of the force for a wide range of generic conditions and could be used for design and analysis of sensors and actuators exploiting this rarefied flow effect. [ABSTRACT FROM AUTHOR]

We have investigated the fl ow regions of the vortex-source combination with a constant pressure established due to the specially chosen intensity distribution of the energy exchange sources (heat input and heat removal) in the space of similarity parameters initial coordinate (temperature)-gas circulation-length of the energy exchange zone. Regions in which a thermal crisis is realized and steady fl ow choking occurs have been determined. We have constructed boundaries of the thermal crisis regions in the following cases of vortex-source combination outflow: into a vacuum, from a rarefied space, into a submerged space or from a submerged space. [ABSTRACT FROM AUTHOR]

Plane thermal transpiration o f a rarefied gas between two walls of Maxwell-type boundaries with different accommodation coefficients is studied based on the linearized Boltzmann equation for a hard-sphere molecular gas. The Boltzmann equation is solved numerically using a finite difference method, in which the collision integral is evaluated by the numerical kernel method. The detailed numerical data, including the mass and heat flow rates of the gas, are provided over a wide range of the Knudsen number and the entire range of the accommodation coefficients. Unlike in the plane Poiseuille flow, the dependence of the mass flow rate on the accommodation coefficients shows different characteristics depending on the Knudsen number. When the Knudsen number is relatively large, the mass flow rate of the gas increases monotonically with the decrease in either of the accommodation coefficients like in Poiseuille flow. When the Knudsen number is small, in contrast, the mass flow rate does not vary monotonically but exhibits a minimum with the decrease in either of the accommodation coefficients. The mechanism of this phenomenon is discussed based on the flow field of the gas. [ABSTRACT FROM AUTHOR]

Abstract: Most of numerical methods for deterministic simulations of rarefied gas flows use the discrete velocity (or discrete ordinate) approximation. In this approach, the kinetic equation is approximated with a global velocity grid. The grid must be large and fine enough to capture all the distribution functions, which is very expensive for high speed flows (like in hypersonic aerodynamics). In this article, we propose to use instead different velocity grids that are local in time and space: these grids dynamically adapt to the width of the distribution functions. The advantages and drawbacks of the method are illustrated in several 1D test cases. [Copyright &y& Elsevier]

Abstract: An experimental analysis of the interaction of a rarefied jet plume with a cylinder-plate system is presented. The main goal is to show that the gas rarefaction can change the distribution of pressure between the two bodies quite unpredictably. The geometrical configuration has been proposed as test case to investigate the development of plume that are typically present in complex structures on spatial satellite. The results are qualitatively in a good agreement with analogous experiments and numerical simulations. [Copyright &y& Elsevier]

Abstract: An approach to model a transient flow of rarefied gas through a long capillary based on numerical data for flow rate previously obtained from the linearized and stationary kinetic equation was proposed. As an example, non-steady flow through a long circular tube connecting two reservoirs is considered. Pressures in the reservoirs and flow rates in the inlet and outlet are obtained as a function of time. It is shown that the behaviors of these quantities vary by changing the gas rarefaction from the free-molecular regime to hydrodynamic one. The typical time to reach the equilibrium state is calculated. [Copyright &y& Elsevier]

Highlights: [•] A generic multiphase DNS method for rarefied particulate flows with heat transfer. [•] Investigations of the settling behaviour of particles with internal heat sources. [•] Thermal levitation is significantly less likely under rarefied conditions. [ABSTRACT FROM AUTHOR]

The second Stokes problem concerning the behavior of a rarefied gas in the half-space bounded over a plate undergoing harmonic in-plane oscillations is solved analytically using the Bhat-nagar-Gross-Krook equation with Cercignani boundary conditions for gas molecules reflecting from the wall. The distribution function of the gas molecules is constructed. The gas velocity in the half-space and near the wall, the drag force exerted by the gas on the boundary, and the energy dissipation rate per unit area of the oscillating plate are found. [ABSTRACT FROM AUTHOR]

Hydrodynamic mix in inertial confinement fusion capsules produces chunk mix between deuterium–tritium fuel and inert pusher materials. The characteristic size of the intermingled fuel and pusher materials can be rapidly reduced by fluid mix, especially when the streamlines of the flow field are chaotic. This leads to an increasing Knudsen number for the fuel segments and a decreasing size of the pusher remnant with respect to the fuel ion mean-free-path. The former exacerbates Knudsen layer yield degradation due to fast ion losses, while the latter tends to alleviate Knudsen layer yield reduction due to other kinetic effects such as diffusive tunneling. [ABSTRACT FROM AUTHOR]