Fluid Dynamics最新文献

Abstract

A model for the numerical study of radiation behind the front of a strong shock wave in a CO₂-N₂ gas mixture is proposed. The model is based on the direct statistical simulation Monte Carlo method and takes into account the physicochemical properties of atoms and molecules, translational-rotational and translational-vibrational energy transfer, kinetics of chemical reactions, excitation of electronic levels of atoms and molecules, as well as the processes of radiative energy transfer. A series of calculations of the spectral characteristics of a shock-heated mixture has been carried out. The results obtained are compared with the available experimental data.

Abstract—A fluid layer of finite depth described by Euler equations is considered. The ice cover is modeled by a geometrically non-linear elastic Kirchhoff–Love plate. The trajectories of liquid particles under the ice cover are found in the field of a nonlinear surface traveling wave tending to a periodic wave at infinity: the so-called “dark soliton” (which is a nonlinear product of a step-wave and a periodic wave) of small but finite amplitude. The presence of dark solitons in the system is an indicator of the modulation stability of the carrier periodic wave (defocusing). The analysis uses explicit asymptotic expressions for solutions describing wave structures on the water–ice interface such as dark solitons, as well as asymptotic solutions for the velocity field in the liquid column generated by these waves.

Abstract

Changes in the regimes of condensate film flow along the underlying surface in the presence of a body force are considered within the framework of a simplified physical and mathematical model of hydrodynamic and thermal processes occurring under unsteady film condensation on a vertical semi-infinite plate. The model is used to determine the applicability conditions of the zero-gravity approximation when considering film condensation. It is found that the validity of using the zero-gravity approximation to calculate the film thickness growth rate on any plate section depends not only on the magnitude of the body force, but also on time and distance between this section and the leading edge of the plate.

Abstract

The problem of two-phase flow of incompressible fluids through anisotropic porous media in the gravity field is considered. Similarity criteria characterizing the flow directions of the displacing and displaced fluids are determined. The regimes of displacement from an anisotropic formation are classified within the framework of study of numerical solutions to the profile problem of flow through an anisotropic porous medium. It is shown that there are four regimes corresponding to qualitatively different flows. Their effectiveness is compared in terms of the coefficient of fluid extraction from the formation and the displacement sweep factor. The influence of the capillary pressure on the displacement efficiency in various flow regimes is studied. It is shown that in some cases increase in the influence of the capillary pressure leads to increase in the displacement coefficient, while in other regimes, on the contrary, to its decrease.

Abstract

The wall pressure fluctuation fields on fairing surfaces and in the surrounding turbulent boundary layer are experimentally investigated. The fairings were in the shape of semi-ellipsoids and were mounted on the wall of a subsonic low-noise wind tunnel. Their heights amounted to 25% of the oncoming boundary layer thickness. The main physical features of the flows under consideration are determined by means of the surface oil-flow visualization. The fluctuating wall pressure field is compared with the flow pattern. It is shown that the greatest pressure fluctuation levels are recorded in the nose region of the fairing surface. It is established that lengthening the model leads to a considerable reduction of the pressure fluctuation strength in the region of flow separation from the fairing surface.

Abstract

The results of study of the initial stage of expansion of a collisionless plasma with the electric current into a plane vacuum gap on the basis of kinetic equations for electrons and ions and the Poisson equation for the electric field are given. Self-consistent dynamics of a two-component plasma and electric field are theoretically modeled and the fundamental mechanism for establishing superthermal velocities of charged particles is described in detail. The parameters of anode-directed flows of positive ions in the cathode plume plasma are calculated. The expansion velocities of the cathode plume plasma observed in vacuum arcs at the level of (1−5) × 10⁶ cm/s can be explained within the framework of the proposed collisionless mechanism.

Abstract

Convection of an electrical conducting MHD nanofluid confined between horizontal infinite boundaries subjected to double diffusion and Hall current is studied analytically. The energy equation contains the terms representing regular heat diffusion, Brownian diffusion and thermophoresis of nanoparticles and the salt diffusion equation contains the regular salt diffusion term. The boundaries are sustained at constant heat and salt but to overcome the inaccuracy produced due to the unrealistic constant flux of nanoparticles, it is taken as zero on the boundaries. The analysis is directed through the normal mode technique led by Galerkin weighted residual method. It is found that the Rayleigh number is reduced due to the presence of nanoparticles while it increases due to the solutal diffusivity. Thus, nanoparticles are responsible for earlier convection and the presence of salt delays it. The Hall currents that usually destabilize the systems are having dual character. It is also shown that for aluminum water nanofluid the oscillatory convection does not exist. The effects of flow parameters have been picturized through individual and comparative graphs.