Home – Home – Jornals – Thermophysics and Aeromechanics 2015 number 2

Results of an experimental study of the structure, the phase composition, and the mechanical properties of laser-welded joints of 3–mm thick titanium and 12Kh18N10T steel sheets obtained with the use of intermediate inserts and nanopowdered modifying additives are reported. It is shown that that such parameters as the speed of welding, the radiation power, and the laser-beam focal spot position all exert a substantial influence on the welding- bath process and on the seam structure formed. In terms of chemical composition, most uniform seams with the best mechanical strength are formed at a 1–m/min traverse speed of laser and 2.35–kW laser power, with the focus having been positioned at the lower surface of the sheets. Under all other conditions being identical, uplift of the focus to workpiece surface or to a higher position results in unsteady steel melting, in a decreased depth and reduced degree of the diffusion-induced mixing of elements, and in an interpolate connection formed according to the soldering mechanism in the root portion of the seam. The seam material is an over-saturated copper-based solid solution of alloying elements with homogeneously distributed intermetallic disperse particles (Ti(Fe, Cr)₂ and TiCu₃) contained in this alloy. Brittle fracture areas exhibiting cleavage and quasi-cleavage facets correspond to coarse Ti(Fe, Cr)₂ intermetallic particles or to diffusion zones primarily occurring at the interface with the titanium alloy. The reported data and the conclusions drawn from the numerical calculations of the thermophysical processes of welding of 3–mm thick titanium and steel sheets through an intermediate copper insert are in qualitative agreement with the experimental data. The latter agreement points to adequacy of the numerical description of the melting processes of contacting materials versus welding conditions and focal-spot position in the system.

Based on the spectral expansion of Euler correlation of the carrier medium the authors have obtained a closed system of functional equations for the Lagrange spectra of heavy inertial particles and the velocity fluctuations of the carrier medium on the particle trajectory. To split the fourth moments the approximation of quasinormality and velocity fluctuations of particles is performed by a random Gaussian process. The approximate self-consistent method is proposed for solving the resulting system of functional equations. The spectrum of Euler correlations of medium velocity fluctuations is modeled by Saffman and Karman distributions. The influence of the spatial microstructure of turbulence, the particles inertia and velocity slip on the intensity of chaotic motion and the coefficient of turbulent diffusion of dispersed particles has been studied.

The study was performed on features of eddy transport of momentum and heat in the lower atmosphere, which includes the planetary boundary layer as well as upper troposphere and lower stratosphere; the study used a three-parametric method for modeling of stratified turbulent flows. A focus was put on analysis of behavior of vertical diffusivities of momentum and heat: data were obtained through direct measurements and through simulation with three-parametric turbulence model with account for effects of internal gravitational waves which support momentum transfer under condition of very stable stratification (while possessing considerable wavy dynamics). It was demonstrated that the profile of vertical diffusivity for momentum, which was calculated using three-parametric turbulence model, is in agreement with data on direct measurements when measured either within a stable stratified planetary boundary layer or beyond this layer, in free atmosphere.

The flow in a far turbulent wake of a towed body has been modeled with respect to the density Froude number in a linearly stratified medium. It is shown that at sufficiently high values of the density Froude number, there is a similarity of the parameters of the wake and of the internal waves generated by it.

The topological features of the structure of combustion products flow in the flow paths with different shapes of channel cross sections at power installations are considered. The results of mathematical modeling of internal gas dynamics of the flow paths of power installations are compared with experimental data.

A new system of equations has been derived to simulate the dynamics of long-wave perturbations on the surface of a thin layer of viscous liquid, flowing down a vertical plane and blown by co-current turbulent gas flow. The analysis of linear stability of the unperturbed flow has been performed. It has been found that at moderate Reynolds numbers of liquid, Benjamin linear model and model of boundary conditions transfer to the unperturbed level for a disturbed gas flow give qualitatively similar results. With decreasing Reynolds number differences between the results obtained by different turbulence models become more pronounced. In the case of small Reynolds numbers of fluid, the system of equations results in a single evolution equation for film thickness deviation from the undisturbed level. Some solutions of this equation have been considered.

A numerical analysis of spatial laminar regimes of natural convection in an enclosure is conducted in the presence of a uniform magnetic field. The mathematical model formulated in dimensionless natural variables “velocitypressuretemperature” has been implemented numerically by the method of control volume. The influence of the Rayleigh number (10³ ≤ Ra ≤ 10⁵) and the Hartmann number (0 ≤ Ha ≤ 100), the orientation of the magnetic induction vector (0 ≤ φ ≤ π / 2) as well as of the geometric parameter (0.2 ≤ A ≤ 5), which reflects the enclosure relative length, on the velocity and temperature distributions as well as the average Nusselt number on a typical isothermal boundary has been studied in detail. A possibility of describing the integral heat exchange in the spatial object under consideration on the basis of the two-dimensional model has been established.

This study investigates analytically the hydrodynamic and thermal behaviour of a fully developed natural convection flow in a vertical micro-porous-annulus (MPA) taking into account the velocity slip and temperature jump at the outer surface of inner porous cylinder and inner surface of outer porous cylinder. A closed – form solution is presented for velocity, temperature, volume flow rate, skin friction and rate of heat transfer expressed as a Nusselt number. The influence of each governing parameter on hydrodynamic and thermal behaviour is discussed with the aid of graphs. During the course of investigation, it is found that as suction/injection on the cylinder walls increases, the fluid velocity and temperature is enhanced. In addition, it is observed that wall surface curvature has a significant effect on flow and thermal characteristics.

The data of the computation of turbulent flow in the CF–π and CP–π configurations of the radial reactor with a fixed bed are presented. The Reynolds motion equations have been solved jointly with the κ–ε turbulence model. To couple the parameters of flows at the interface free part fixed bed the classical continuity equations were used. The computational data are obtained for the averaged and turbulent characteristics, and it is shown that the flow in the fixed bed causes the generation of the turbulence kinetic energy and its dissipation rate; the flow in the CF–π configuration is distributed more uniformly as compared to the CP–π configuration of the radial reactor. Computed data are compared with the experimental ones.

The features of gas hydrate formation at gas injection into a porous medium, initially filled with gas and ice, are investigated. The self-similar solutions to the single-dimensional problem, describing distribution of the main parameters in a layer, were derived. It is shown that there are the solutions, according to which the gas hydrate formation can occur in three different regimes. The critical diagrams for such regimes are plotted.

Resistance to destruction of metallic and nonmetallic objects in high-temperature supersonic flow was studied in experiments. The significant role of gas-dynamic structures on the zone of heat-up and ignition of metals was demonstrated. As the critical temperature was achieved, sample combustion or erosion commences, thus determining the sample destruction rate.

February 20, 2015 marked the 90th anniversary of Professor Evgeniya M. Khabakhpasheva, Honored Scientist of Russia and Doctor of Technical Sciences.

April 24, 2015 is the 70th anniversary of the distinguished scientist in the field of fluid mechanics, Doctor in Physics and Mathematics, Professor Victor V. Kozlov.