Vol 59, No 5 (2018)

The influence of the molecular structure of gas flows on the characteristics of turbulent flows and the influence of the properties of molecules on turbulent processes have been studied. A review of the results of studies of turbulent processes is presented. Data on flows at the boundary of a supersonic jet and in a pipe with a divergent inlet section, and Hagen–Poiseuille flow are given. Experimental study of Hagen–Poiseuille flow has shown that the molecular properties of the medium have an effect on the critical Reynolds number. It is shown that in comparing the critical Reynolds numbers for flows of different gases at different pressures, the common determining parameter is the second virial coefficient.

The direct simulation Monte Carlo method was used to study plane–parallel flow of hydrogen through an obstacle formed by a series of parallel infinite wires. Particular attention was paid to the influence of the geometric parameters of the wire obstacle, the degree of rarefaction, and the flow velocity on the degree of hydrogen dissociation due to heterogeneous reactions on the wire surface.

A possibility of using small-scale vacuum setups for experimental investigations of supersonic jets escaping from supersonic nozzles into vacuum or rarefied space is considered. Results of studying the structure of the secondary supersonic flow formed in supersonic jets with developed condensation, which is detected for the first time, are reported. The present investigations are carried out with the use of photometry and spectrometry of jets with the use of radiation excited by an electron beam; flow visualization is also performed. The results obtained in the study are analyzed; capabilities and specific features of various methods of flow registration are considered. An empirical model, which establishes the dependence between the detected secondary flow and the process of formation of large clusters in the flow, is developed and justified.

The process of folding of villin subdomain HP-35 has been studied using the method of molecular dynamics. To characterize protein conformations, two variables are introduced that correspond to the distances between fluorophores in experiments on protein folding with the Förster resonance energy. The simulation results show that the field of probability flows of transitions between protein states is filled with eddies. It has been found that, in contrast to the previously studied cases of hydrodynamic turbulence and turbulence in protein folding in three-dimensional conformational space, the structure functions of the flows of various orders depend linearly on the increment in the conformational space. An explanation of this linear dependence based on the β-model is proposed. It is shown that this dependence is not due to the choice of variables to describe the folding process.

The formation of a fluoropolymer coating by chemical deposition has been studied experimentally. It has been found that increasing the flow rate of the precursor gas leads to a decrease in the growth rate of the coating. Deposition conditions were analyzed, and the gas-dynamic parameters of the process were estimated. The estimates are consistent with experimental data.

A Prandtl slope flow model is generalized for the case with a homogeneous stationary source of a heavy admixture that significantly changes the medium density. A stationary analytical solution for a velocity of arising flows, temperature deviations, and admixture distribution is obtained. The model describes, for example, some special features of the dynamics of a ground snowstorm above a slope surface.

The results of temperature and density measurements of secondary electrons in a free jet of argon, activated in an electron beam plasma, carried out using a Langmuir double electrostatic probe. A cold plasmatron prototype with a primary beam energy of 1 keV is used obtain a jet of dense cold plasma with a cross size of approximately 80 mm and parameters with which silicon layers may be deposited with necessary characteristics in a forvacuum pressure range.

This paper considers the two-dimensional problem of the theory of viscous hypersonic flows formulated for the high-velocity translational-nonequilibrium flow of a monatomic gas past a surface based on macrokinetic 13-moment Grad equations using the model of a two-layer thin viscous shock layer (TVSL) near non-thin bodies. A class of similarity variables is proposed that allows the kinetic problem of the TVSL to be reduced to the well-studied Navier–Stokes problem of the TVSL.

The onset of the Benard–Marangoni convection in a horizontal porous layer permeated by a magnetohydrodynamic fluid with a nonlinear magnetic permeability is examined. The porous layer is assumed to be governed by the Brinkman model; it is bounded by a rigid surface from below and by a non-deformable free surface from above and subjected to a non-vertical magnetic field. The critical effective Marangoni number and the critical Rayleigh number are obtained for different values of the effective Darcy number, Biot number, Chandrasekhar number, nonlinear magnetic parameter, and angle from the vertical axis for the cases of stationary convection and overstability. The related eigenvalue problem is solved by using the first-order Chebyshev polynomial method.

A lumped-parameter mechanical system consisting of a chain of physically related rigid bodies, each of which has one rotational degree of freedom, is considered. It is shown that the inertialess elastic elements connecting the absolutely rigid bodies of the chain can be chosen so that the mechanical structure acquires the properties of a so-called absolute mechanical filter. The motion of any inertial element of this system is described by the equation of a classical harmonic oscillator with one degree of freedom. Using the system considered as an example, it is shown that there is a relationship between the models of classical and quantum mechanics. From the positions of modern classical mechanics, this lumped-parameter system confirms the well-known Einstein’s hypothesis theoretical physics that a rigid body is a system of independent oscillators.

This paper describes an experimental study of a temperature effect on the fracture of laser welded joints of Mg- and Cu-containing aviation aluminum alloys. The fracture of alloys and their welded joints under a uniaxial loading at temperatures of −60, 20, and 85◦C is under study. It is revealed that the strength and ultimate strain of welded joints of Cu-containing alloys decrease as temperature rises because of the formation of fixed zones of localized plastic shears. Heating and cooling suppress the Portevin–Le Chatelier effect and significantly reduce the ultimate strain of a Mg-containing alloy, even though such reduction is not observed in a welded joint. It is shown that, the maximum limiting elongation of the welded joint of a Mg-containing alloy is achieved at a negative temperature, while the formation of secondary cracks is begins during heating.

Ablation of monocrystalline silicon to atmospheric environment induced by a millisecond pulse of an Nd:YAG optical laser with a wavelength of 1064 nm is studied. Shadowgraphy is applied to study the process of monocrystalline silicon plasma expansion for the laser energy density of 955.4–2736.0 J/cm². It is shown that the outer boundary of the plasma plume diffuses outside with time. Plasma expansion occurs in both axial and radial directions, but the velocity of plasma expansion in the radial direction is smaller than in the axial direction. Two centerlines of the laser action are symmetric. The maximum expansion velocity of 162.1 m/s is reached with the laser energy density of 2376.0 J/cm², and a laser-supported combustion wave is generated in this case. In contrast to monocrystalline silicon under the action of a short-pulse laser, the millisecond laser action can make the plasma expansion velocity increase for the second time. A material splash can be observed from the expansion images in the case of a high laser energy density.