L. Marino

Gas flow in a permeable medium

The dynamics of gases in permeable media is approached both experimentally and by numerical simulations. The experiments were performed in matrices made of packed beds of spheres in rarefied conditions and a model for the direct simulation of the molecular kinetics is proposed. Comparisons between experimental data and numerical results show the influence of the main parameters of the gas–solid interaction and the range of validity of the model. Moreover it is shown that there is a flow condition for the minimum permeability of the medium to the gas flow. Such a minimum depends upon the Knudsen number, and can be explained by the molecular dynamics as in the well-known Knudsen’s experiment on capillaries.

Effects of the Centrifugal Forces on a Gas Between Rotating Cylinders

The gas e ow between two concentric rotating cylinders is investigated over a wide range of governing dimensionless products. Analytic solutions are given for the free molecular e ow, for the Bhatnagar ‐Gross‐Krook model up to the e rst-order approximation, and for the hydrodynamic limit in the Chapman ‐Enskog expansion. The slip e ow boundary conditionsareextensively discussed, and a constructivesolution to the transitional e ow is proposed. Numerical direct simulation data are obtained and adopted as exact reference experimental results.

Slip flow and temperature jump on the impulsively started plate

Abstract The unsteady compressible boundary layer equations over an impulsively started flat plate are firstly solved subjected to velocity slip and temperature jump conditions. Comparisons are carried out with existing solutions. Then the conjugate problem for a slab of finite thickness is dealt, when the fluid dynamic field is coupled with the thermal field in the solid.

Stability and admittance of a channel flow over a permeable interface

The stability and the admittance analysis are considered for a Poiseuille flow running over a permeable slab. The case where a suction, due to a cross flow, is present through both the channel and the porous slab is also dealt with. An analytic solution is found for the basic flow in the entire field whereas the stability analysis and the evaluation of the admittance at the interface are numerically carried out. The errors made in the usually simplified analyses are fully discussed.

Simulation and modelling of flows between rotating cylinders. Influence of Knudsen number

The equations which govern a number of models for flows between rotating cylinders at different Knudsen numbers are solved numerically by means of the direct simulation Monte Carlo method (DSMCM) to show their limitations. The DSMC code was firstly tested and validated against existing experimental data and then its results represented the reference data base for evaluating the characteristics of each model.

A model for the compressible flow through a porous medium

A model for a continuum gas flowing through a porous matrix is proposed where the gas kinetics is governed by the Boltzmann equation and the solid phase by the energy equation. In the Boltzmann equation the integral relative to the gas–solid collisions is evaluated as for the collisions of hard spheres molecules against much heavier and longer straight particles (Lebowitz model of a sticks gas), randomly distributed in space according to a Maxwellian function with zero mean velocity. The mean flow is one-dimensional but the molecules are free to move in all three space dimensions. In the continuum limit, the moments of the Boltzmann equation provide the mass continuity, energy and momentum equations, the last one expressing the Darcy law for a compressible gas. The transport coefficients are analytically evaluated and a few examples are dealt with.

Numerical experiments on the gas flow between eccentric rotating cylinders

A numerical experiment was carried out on the gas flow field between two eccentric cylinders, one of which is rotating. Attention was paid to the presence of separated recirculating regions from the continuum to the rarefied regimes. The direct simulations were performed by means of a Monte Carlo (DSMC) method and bi-polar co-ordinates were adopted. The calculations were relative to isothermal walls at the same temperature. Streamlines and velocity profiles were evaluated as functions of the Knudsen number, of the Mach number and of the geometric parameters. The gas considered was argon. Copyright

Reference frame influence on transport phenomena in gases. A direct simulations approach

Abstract In this paper, the effects of the observation frame on momentum transport and energy transfer in gases are considered. A numerical method of direct simulation is adopted for evaluating the shear stress distribution and the heat flux in the fluid-dynamic field between two rotating walls in a range of Knudsen numbers from free molecular flow to compressible continuum. The numerical solutions are compared with the analytical results where existing. It is shown that the effects of the reference frame increase either with the gas rarefaction or with the angular speed of the frame. With respect to the theoretical debate on the material frame indifference of the transport characteristics in a gaseous continuum, the simulations confirm that the frame dependence vanishes (below the numerical error) as the Knudsen number tends to zero.

Flow separation between rotating eccentric cylinders

Abstract We deal with the dynamic and thermal characteristics of the rarefied flow between two eccentric isothermal cylinders one of which is rotating. A numerical program of direct simulation which is based on a Monte Carlo (DSMC) procedure was adopted and the main results concern the influence of the Knudsen and Mach numbers, and of the eccentricity on the location and extent of the flow separation. Part of the flow domain is shown to be cooler than the wall temperature, and the extent of this region decreases with an increasing gas rarefaction.

Rarefied flow through a packed bed of spheres

In this paper we present experimental results for flows through packed bed of spheres, in cases where the flow characteristics can be classified in a range from the velocity slip regime to the transition and free molecular flows. A simple simulation model is also proposed and solved by means of a MonteCarlo code, and comparisons between results of numerical calculations and experimental data are also reported.