The aim of this work is to construct an algorithm for visualizing a polydisperse phase of solid particles (dust) in an inhomogeneous flow of a two-phase gas-dust mixture that would allow us to see, within one plot, the degree of polydispersity of the dust phase and the difference in the spatial distributions of individual fractions of dust particles in the computational domain. The developed technique allows us to reproduce concentrations from one to three fractions of dust particles in each cell in the computational domain. Each of the three fractions of dust particles is mapped to one of the main channels of the RGB palette.The intensity of the color shade is set to be proportional to the relative concentration of dust particles in this fraction. The final image for a polydisperse mixture is obtained by adding images in each of the three color channels. To visualize the degree of polydispersity, I propose depicting the spatial distribution of the entropy of the dust mixture. The definition of the entropy of a mixture is generalized to take into account the states of a mixture with zero number of particles in the mixture. They correspond to dust-free sections of the computational domain (voids). The proposed method for visualizing the polydispersity of a mixture of particles is demonstrated using the example of dynamic numerical modeling of the spatial features of dust structures formed in turbulent gas-dust flows and in flows with shock waves.Real liquid, gas or plasma media have an inhomogeneous structure and are complex, composite systems that include microobjects of different types and different nature, such as small solid suspended particles, droplets or bubbles. There are a huge number of areas in the field of technology in which a person deals with multiphase environments, from chemical reactors to engine building and aeronautics. There are no manifestations of polyphase in nature that are less significant. Despite the small relative mass content, impurity aerosol or dust particles can play an important role in the life of planetary atmospheres, interstellar or intergalactic gas. The dust component determines the optical properties of the medium, its opacity in one interval or another of the electromagnetic spectrum. As a consequence, dust in the atmosphere or in the interstellar gas can act as a coolant, realizing the anti-greenhouse effect [1,2]. Due to their windage, dust grains can cause an effective mechanical effect of star radiation on a transparent neutral gas, accelerating under the influence of radiation pressure and accelerating the surrounding matter [3,4]. Particles of dust in the interstellar gas act as a catalyst for the process of gas molecularization [1]. Dust also serves as a building material for the formation of solid celestial bodies, such as asteroids or planets [1].Examples of space objects enriched with impure dust particles are gas-dust interstellar clouds and nebulae, protoplanetary disks, spiral arms of galaxies and gas-dust halos of galaxies. Usually, cosmic dust grains are par...
A large number of publications have been devoted to studying the features of the flow in two-phase flows in a gas-dispersed flow with inertial dust particles (shock waves, jets, turbulence, regular structures such as plasma crystals). In recent years, the study of the behavior of various fractions of impurity particles in polydisperse dust mixtures, expressed in the spatial separation of their distributions, has been of increasing interest. Spatial variations of individual components of the dust mixture make it possible to diagnose the state of the carrier gas phase in those cases when the carrier phase is very rarefied and cannot be observed directly (interstellar gas). This work is a continuation of the authors’ work [14], in which an original algorithm was proposed based on the use of three-dimensional color space resources, which allows visualizing spatial distributions of concentrations of up to three fractions of a polydisperse mixture of dust particles simultaneously, as well as an entropy measure that allows visualizing the degree of polydispersity in a heterogeneous gas-and-dust environment. However, the structural features of the impurity phase (caustics, areas of segregation of dust particles by their size, mass, etc.) are not necessarily spatially combined with its dynamic features (collisionless shock waves, flow turning points, stagnation points, accumulation points). In this paper, we propose a method for visualizing the dynamic features of a polydisperse collisionless mixture of particles in a two-phase gas-dust medium by constructing spatial distribution maps of the particle velocity dispersion anisotropy regions. Strong anisotropy of the velocity dispersion corresponds to the region in which an intense multi-stream flow occurs. Dust is considered as a mixture of several fractions, each of which contains particles of the same type, while the particle sizes in different fractions are different. For each dust fraction, a field is constructed of the spatial distributions of the eccentricities of the velocity dispersion ellipses. To visualize the degrees of anisotropy of the velocity dispersion of two fractions of a polydisperse dust mixture at once, a specially selected entropy measure is proposed. The results of two-dimensional demonstration calculations of a turbulent gas-dust medium and the anisotropy map in the distribution of the velocity dispersion of an impurity dust component are presented.
A two-dimensional model of the flow of the gas-dust interstellar medium in the vicinity of the spiral arm of the galaxy is constructed. The flow in a vertical plane transverse to the disk plane is considered. The effects of nonadiabatic flow (volumetric heating and cooling of the gas by radiation) are taken into account. The balance of heating and cooling ensures the coexistence of two phases, cold parsec-sized clouds of atomic hydrogen and warm intercloud gas. The consideration includes polydisperse dust, represented by three fractions of particles of different sizes and masses. Dust particles have finite inertia, their movements do not exactly repeat the movement of gas. Turbulence in the disk and in the spiral arm is also taken into account. Models are considered that use different combinations of the location of turbulence sources in the disk and/or in the arm. The main results obtained by the methods of computer hydrodynamic modeling are as follows. Clouds undergo significant transformations as they pass through the spiral arm. A significant part of the clouds is absorbed into a thin dense cloud layer, which extends in a spiral arm along the equatorial plane in the vicinity of the center of the arm and has a size of approximately half the width of the arm. A smaller part of the clouds passes without destruction or with partial destruction through the sleeve, experiencing strong deformations along the way. The small-scale cloud component is partially restored under the action of turbulence, which perturbs the extended cloud layer inside the arm and partially destroys it into separate fragments. A wedge-shaped galactic shock wave is formed on the rear side of the arm with respect to the incoming gas flow, attached to the rear edge of the extended cloud layer. A flow limited by a shock wave has the character of a jet that performs quasi-periodic transverse oscillations. The reason for the oscillations, apparently, is the instability of the shear flow, since tangential discontinuities are formed inside the jet along the flow and at a small angle to the shock fronts. Dust particles are dragged by turbulent eddies and carried to heights of 150–200 pc above the disk plane, which naturally explains the existence of chaotic filamentous dust structures extending above the galactic disk to heights of several hundred parsecs. The grains of dust are distributed differently inside the vortices. Dust grains with sizes of 0.01-0.1 μm cluster more easily than larger dust grains with a radius of 1 μm. Turbulence serves as a mechanism to effectively trap dust particles on the front side of the spiral arm. Modeling shows that dust lanes are more pronounced on the front side of the arm.
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