V.G. Sultanov

Chelyabinsk superbolide explosion in the Earth’s atmosphere: A common phenomenon or unique coincidence?

The paper analyzes the disintegration of small cosmic bodies in a planetary atmosphere and most important facts observed during the fall of the Chelyabinsk superbolide: its speed loss during passage through the upper atmosphere, its strength and the character of destruction, the altitude of its explosion, and the energy release. Detailed data are presented on the aerodynamic phenomena accompanying the supersonic atmospheric entry and destruction of the superbolide. The strength of the original meteorite is evaluated as a function of its initial disintegration altitude. Principal data obtained on the collision between comet Shoemaker-Levy 9 and Jupiter are reported.

The origin of extensional flow in a channel with sudden contraction and expansion

The pressure driven flow of a viscous incompressible fluid in a 2D channel with sudden contraction and expansion is investigated numerically. The attention is concentrated on studying conditions of occurrence of the elongational flow in a narrow section of the channel. To this end, interconnection between flow patterns and axial velocities is analyzed at different Reynolds numbers.

Mathematical modeling of converging detonation waves at multipoint initiation

The methods of mathematical modeling based on the latest experimental data are proposed to conduct a study of the cylindrical detonation process and gas dynamics of the explosion products. The numerical simulation of converging cylindrical detonation waves at multipoint initiation for the recent experiments in IPCP RAS was conducted. The results of the numerical simulation and the experiment are compared.

NUMERICAL MODELLING OF DEEP IMPACT EXPERIMENT

The Deep Impact active space experiment has been done to study a hypervelocity collision of a metal impactor with the nucleus of the comet 9P/Temple 1. In this work we present results of numerical modeling in comparison with corresponding experimental data. The modeling has been done with the use of 3D “finite‐size particle in cell” method. The computational setup corresponded to impact angle of 30 degree with respect to the horizon for different materials forming the surface of the comet nuclei, i.e. ice and sand. Conclusions are made for the possible composition of the comet.

Features of behavior of the contact boundary of metals during explosion welding: Numerical simulation

The results of numerical simulation of wave formation under an oblique impact of metal plates during explosion welding are presented. The numerical simulation was carried out on the basis of the elastoplastic approximation. It is shown that the elastoplastic behavior of metals may be a possible source of instabilities. Further evolution of the process of wave formation and the formation of a periodic wave structure of the interface are already determined by the hydrodynamic behavior of materials. The temperature at the contact boundary of plates obtained in the calculation exceeds the melting point. The calculated wavelengths coincide with the experimental data.

Deformation Behavior of a Composite Drop in a Simple Shear Flow

The hydrodynamics of disperse liquid mediaattracts increased attention, first of all, owing to theirnumerous applications in various industries (chemical, medical, pharmaceutical, processing of polymers,etc.). The theoretical analysis of such systems is basedon studying the dynamic behavior of an isolated dropin a flow for determining the strain, orientation, andstability of the drop in various flow modes. To date, anextensive body of experimental data on the mechanisms of deformation and breakup of homogeneousdrops has been accumulated [1–6]. However, thehydrodynamic behavior of composite drops containing one or several internal inclusions (cores) remainslittle studied. At the same time, such objects have adiversity of applications: from increasing the impactresistance of mixed polymer composites to targeteddrug delivery [5, 6]. Therefore, the comprehensiveinvestigation of composite drops is of fundamental andpractical interest.Studying the hydrodynamic behavior of such dropsis complicated by a number of difficulties related to thenecessity of taking into account a large number ofparameters and also the dynamic changes in theshapes of both inner and outer interfaces. In the simplest case, a composite drop consists of a single coreand a shell, which are immersed in a dispersion liquid(Fig. 1). In this case, features of the deformation andshaping of the drop are determined by the relative values of the surface tensions at the interfaces betweenthe components of the medium, their viscosities, andalso the core size as compared to the shell size.It was previously shown that, in a shear flow, a corewith low viscosity and low surface tension takes theshape of an extended dumbbell rotating in the direction of the flow [7]. In this work, we studied the hydrodynamic behavior of a twodimensional compositedrop in which the viscosity of the core is much higherthan that of the shell and also the core–shell interfacial tension significantly increases the surface tensionat the interface between the shell and the dispersionliquid. In such a formulation, the main contribution tothe total strain and orientation of the composite dropIs made by the transformation of the shape of the shell.The deformation and dynamic structuring of this typeare also characteristic of swollen microgels immersedin a thermodynamically incompatible liquid [8–10].Comparison of the hydrodynamic behaviors of composite and homogeneous drops enabled one to understand the effect of flow perturbations caused by thepresence of the viscous core on the deformationbehavior of the composite drop.

Mechanism of stability of the shear flow of a two-layer system of viscous liquids

171 The evolution of the morphology of multicompo� nent liquid media in the course of mechanical treat� ment is related, first of all, to the development of hydrodynamic instability at the interface. In the initial stage of the shear flow, this is caused by an exponential increase in the amplitude A(t) = A0e kΔct of capillary waves over a wide range of wavenumbers k. At positive values of the rate of change in the perturbation ampli� tude , the flow is unstable, while at negative values of this rate, it is stable. It was shown (1) that the Cou� ette and Poiseuille shear flows can be destabilized by applying weak longwave perturbations to the inter� face of a twolayer system of incompressible Newto� nian liquids at certain values of the viscosity ratio m and the thickness ratio n of the layers and at arbitrarily low Reynolds numbers. This qualitatively distin� guishes the instability of this type from the transition to turbulent flow. It was demonstrated (2, 3) that the change in the amplitude of short and long waves is caused by a phase shift of the velocity perturbation wave induced by inertial liquid transfer. At the same time, the mechanism of instability of shear flow at arbitrary wavelengths remained unclear. Solving this question requires involving numerical methods of analysis of the equations of momentum transfer of media with nonuniform viscosity distributions. In this work, for the first time, we performed a direct numerical modeling of the simple shear flow instability development of a twolayer system of New� tonian liquids over a wide range of wavelengths. We determined the conditions for the transition between the asymptotic solutions corresponding to longand Δ c shortwave perturbations. We also showed that the inertial shift of vortices of flow rate perturbations is proportional to the growth rate of the interface pertur� bation amplitude.