Fluid Dynamics

When the supersonic solar wind interacts with the oncoming flow of the interstellar medium, a gas-dynamic structure called the heliospheric shock layer is formed. It consists of a tangential discontinuity (called the heliopause in astrophysics), a solar wind deceleration shock wave (or heliospheric shock), and a bow shock in the interstellar medium. The distance to the heliospheric shock layer, as well as its thickness, are significantly influenced by magnetic fields (heliospheric and interstellar), as well as by interstellar hydrogen atoms, which interact with solar wind plasma and the interstellar medium through charge exchange. The influence of electron thermal conductivity, which is anisotropic and acts along magnetic field lines, is considered. Particular attention is given to the tail of the interaction region. It is shown that taking thermal conductivity into account leads to a decrease in the thickness of the inner portion of the shock layer between the heliospheric shock wave and the tangential discontinuity. It is found that the influence of thermal conductivity significantly alters the plasma temperature and density, which may prove significant when analyzing the absorption spectra in the Lyman-alpha line in the heliosphere’s tail region.

A mathematical model of the process simulating the explosions of small celestial bodies in the inhomogeneous atmosphere of the Earth at a certain height above its surface is proposed. A hypothesis has been put forward about the structure of the Vitim space body chosen as an example, which is an icy core of an ex-comet overgrown with a thick refractory crust, that is, a pseudoasteroid object. The complete system of three-dimensional Euler equations for an ideal compressible gas in Cartesian coordinates was used as the initial one. To solve the discrete analog, a flow-through counting scheme based on an explicit difference method was developed. Based on the data obtained during the work of scientific expeditions to identify the damage caused by the explosion of the Vitim meteoroid to the taiga forest, the main parameters of this explosion were selected – its power and height, which gave the results of calculations of the size of zones of terrestrial vegetation destruction, approximating the actual.

This study examines the propagation of spatial wave in a layer of magnetic fluid bounded by air, within the framework of linear theory. The wavelength considered exceeds the thickness of the fluid layer. An approximation of the fluid’s magnetization curve is derived. The effects of gravity, magnetic force, and surface tension are taken into account. The wave vector is assumed to form an arbitrary angle with the direction of the applied horizontal magnetic field.

The paper presents a solution to the problem of experimental modeling—using a compact vacuum facility—of gas or liquid jet outflow from nozzles that simulate spacecraft (SC) nozzles, under conditions of a highly rarefied environment. The use of modern equipment, the development and mastery of diagnostic tools, and accumulated experience have enabled model experiments to reproduce and study the distribution of flow parameters, as well as the gas-dynamic interaction of jets with each other and with the environment surrounding the SC. The main methods for diagnosing gas flows in vacuum, which have been tested and are in use at the facility, are described. Examples of obtained results are provided, demonstrating the wide range of information acquired. In addition to supersonic gas flows from sonic and supersonic nozzles, as well as block configurations—primarily in condensation regimes—the setup has allowed for the realization of steady liquid outflow into vacuum. Such jets have been visualized under various outflow and environmental rarefaction conditions.

The article presents the results of experimental studies on gas-dynamic heating of gas near the blind end of a deep resonant Hartmann-Sprenger cavity. The effect of the initial pressure in the prechamber on the dynamics of gas heating is investigated. The duration of the experiments carried out in the acousto-convective setup of the ITAM SB RAS was 2 hours. The results showed that during operation of the Hartmann gas-dynamic whistle, the equilibrium state is reached in an hour and a half after the start of the experiment. The process of gas heating in the end region of the resonator consists of three stages: an abrupt increase in the first minute; gradual heating over half an hour and reaching the equilibrium state within an hour. When studying the heating of the outer surface of the resonant cavity, it was experimentally confirmed that higher oscillation modes contribute to the intensification of gas heating in deep resonators. At low pressures, at which the Hartmann effect is not realized, periodic cold and hot areas are formed on the outer surface of the deep resonant cavity.

Numerical and experimental studies on the transition between regular and Mach reflection of steady shock waves and the related hysteresis phenomenon are reviewed. The results of detailed numerical studies are presented, in which, with flow parameters corresponding to the dual solution domain, the dependence of the observed steady shock wave configuration on the initial conditions is demonstrated, and the existence of hysteresis of regular and Mach reflections is shown with varying the angles of the wedges, the free-stream Mach number, the distance between the wedges, and also in asymmetric shock interaction. The results of experimental and numerical studies of the three-dimensional structure of regular and Mach reflections and the effect of the flow three-dimensionality on the transition are presented. The dependence of experimental data on the transition between regular and Mach reflections on the type of wind tunnel and the possible influence of flow disturbances are discussed. The results of numerical studies on the controlled introduction of flow disturbances and the transition between regular and Mach reflections induced by disturbances are presented. We also discuss the results of numerical studies of the transition between regular and Mach reflections and hysteresis in some other flows: overexpanded supersonic jets, chemically reacting gas mixtures, interaction of bow shocks between cylinders, and interaction of hydraulic jumps in shallow water.