Home – Home – Jornals – Thermophysics and Aeromechanics 2017 number 2

On May 18, 1957, the USSR government adopted a historic decree on establishing the Siberian Branch of the Academy of Sciences (SB AS USSR). This was initiated by prominent scientists: academicians M.A. Lavrentyev, S.A. Khristianovich, and S.L. Sobolev, who not only proposed to create a major scientific center in Siberia, but ex-pressed their readiness to move there to work together with their scientific schools.

As a result of long-standing studies of subsonic flows past 2D surface imperfections, physical models to describe the influence of such elements on the boundary-layer transition to turbulence were formulated. The models are primarily based on stability properties of the flow around local geometrical variations of the wall. The present review discusses the mechanisms of boundary layer destabilization by the imperfections revealed by the classical analysis of low-amplitude shear layer oscillations and using recently developed approaches to the local/global modal/non-modal flow stability. While preparing this review, we preferred to trace and briefly outline the main routes of flow turbulization instead of discussing relevant details reported in original publications.

The possibility of using the injection of air into the incompressible turbulent boundary layer of an axisymmetric wing through a finely perforated area provided on the wing surface was studied. The air blowing was implemented via the supply of external pressurized flow through a permeable leading edge of the wing. It is shown that, with the blowing section located on the “flat” side of the wing, only an insignificant reduction in airfoil drag could be achieved. Simultaneously, the data obtained show that there exists a possibility of raising the lift-drag ratio due to a more appropriate choice of blowing-section location in the rarefaction region of the flow.

The recovery ratio of a wedge-shaped hot-film probe was determined in an experi-mental as well as numerical study, since this information is still unpublished and es-sential for using the probe in hot-film anemometry. The experiments were conducted at the Khristianovich Institute of Theoretical and Applied Mechanics (ITAM) in Novosibirsk, Russia, and the simulations were performed with StarCCM+, a com-mercial 2nd order finite volume code. In the analysis, the Mach number was varied be-tween M = 2 and M = 4, and the unit Reynolds number ranged from Re₁ = 3.8x10⁶ to Re₁ = 26.1x10⁶ m^–1, depending on the Mach number. During the experiment, the stag-nation temperature was kept constant for each Mach number at a separate value in the range of T₀ = 289 x 7 K. Three different stagnation temperatures were used in the simulations: T₀ = 259 K, T₀ = 289 K, and T₀  = 319 K. The difference between the ex-perimental and the numerical results is ≤ 0.5 %, and, therefore, both are in very good accordance. The influence of the Mach number, of the unit Reynolds number, and of the stagnation temperature was analysed, and three different fitting functions for the recovery ratio were established. In general, the recovery ratio shows small varia-tions with all three tested parameters. These dependencies are of the same order of magnitude.

Using the previously obtained dependence of excess viscosity on internal energy density and low-parametric unified equation of state for calculation of thermodynamic properties of liquid, gas, and fluid, the equation for the excess viscosity of argon in the range of the “mixed” mechanism of momentum transfer in the shear flow was derived. Different versions of approximation of excess viscosity dependence on the density of interaction energy were compared, and the optimal version of this dependence was determined. A simple unified low-parametric equation was obtained for describing the coefficient of argon viscosity in a wide range of state parameters. It is shown that the proposed low-parametric equation for calculating the viscosity coefficient of liquid and gas allows reliable extrapolation beyond the studied region.

This paper presents experimental and simulation results of cold spray coating deposi-tion using the mask placed above the plane substrate at different distances. Velocities of aluminum (mean size ~ 30 µm) and copper (mean size ~ 60 µm) particles in the vicinity of the mask are determined. It was found that particle velocities have angular distribution in flow with a representative standard deviation of 1.5–2 degrees. Modeling of coating formation behind the mask with account for this distribution was developed. The results of model agree with experimental data confirming the importance of particle angular distribution for coating deposition process in the masked area.

The work is devoted to the determination of main peculiarities of the two-phase mix-ture formation in the flow duct of the gas-dynamic ignition system. The paper presents a mathematical model and the results of a numerical and experimental investigation of the peculiarities of the unsteady gas flow as well as the processes of the fragmentation and evaporation of droplets in the resonance cavity of the gas-dynamic ignition system. Different configurations of injectors for liquid supply are considered, and the influence of the most significant factors on heat release and concentration of the evaporated liquid in the resonance cavity is investigated. The obtained data may be used for choosing the injectors and the regimes of the liquid fuel supply, which enable one to ensure the stable conditions for igniting two-phase fuel mixtures in the gas-dynamic ignition system.

The Pontryagin equation was applied to calculating the average time for the random process escaping the assign interval: this gives the average delay time for waiting of particle ignition moment in a turbulent flow of gas. A direct numerical simulation method was developed for gas temperature fluctuations with assigned autocorrelation function and particle temperature fluctuations due to exothermal chemical reaction. The method was based on numerical solution of a system of stochastic differential equations. Results of direct simulation were validated through comparing with the analytical solution available for particles without exothermal reaction. Analytical calculations and results of direct numerical simulation for the delay time of particle ignition are in agreement.

An approach to the determination of the heat and mass transfer coefficients from dis-persed particles by the development of the hydrodynamic analogy is considered. The equations for computing the heat and mass transfer coefficients in continuous phase at a laminar regime of the flow around solid particles as well as the mass transfer coefficients in droplets are obtained. Comparisons with the experimental data of dif-ferent authors are presented.

The phenomenon of the intensification of convective heat transfer through air cavities under the conditions of their axial rotation and external heating based on the rise of centrifugal body forces in differently heated air medium has been substantiated theo-retically and confirmed experimentally. The criterion dependencies for convection coefficients of axisymmetric cylindrical and conical closed air cavities subjected to external heating and axial rotation have been obtained using the results of the physical and numerical experiments. Both single-layer cylindrical cavities and two-layer ones with perforating internal orifices have been considered.

The present work is performed to study the effect of heat generation on fully devel-oped flow and heat transfer of micropolar fluid between two parallel vertical plates. The rigid plates are assumed to exchange heat with an external fluid by convection. The governing equations are solved by using Crank–Nicolson implicit finite difference method. The effects of governing parameters such as transient, heat generation, mi-cropolar parameter, Prandtl number, Biot number, and Reynolds number on the veloc-ity and temperature profiles are discussed. It is found that the presence of heat generation enhances the velocity and temperature of the micropolar fluid at the middle of the channel.

The nonlinear problem of non-stationary heat conductivity of the layered anisotropic heat-sensitive shells was formulated taking into account the linear dependence of thermal-physical characteristics of the materials of phase compositions on the tem-perature. The initial-boundary-value problem is formulated in the dimensionless form, and four small parameters are identified: thermal-physical, characterizing the degree of heat sensitivity of the layer material; geometric, characterizing the relative thick-ness of the thin-walled structure, and two small Biot numbers on the front surfaces of shells. A sequential recursion of dimensionless equations is carried out, at first, using the thermal-physical small parameter, then, small Biot numbers and, finally, geome-trical small parameter. The first type of recursion allowed us to linearize the problem of heat conductivity, and on the basis of two latter types of recursion, the outer asymptotic expansion of solution to the problem of non-stationary heat conductivity of the layered anisotropic non-uniform shells and plates under boundary conditions of the II and III kind and small Biot numbers on the facial surfaces was built, taking into account heat sensitivity of the layer materials. The resulting two-dimensional boundary problems were analyzed, and asymptotic properties of solutions to the heat conductivity problem were studied. The physical explanation was given to some aspects of asymptotic temperature decomposition.

The growth rate of the liquid contact layer may be influenced by an electric current at contact melting. Depending on the direction, the electric current speeds up or slows down the liquid layer growth in comparison with the diffusion regime (no-current mode). It is shown that if the current flowing in the "accelerating" direction is de-creased inversely proportional to the square root of time, the time law of the liquid layer growth will be identical to the diffusion mode. The proposed pseudo-diffusion mode is implemented for the bismuth-indium system at 75°C. Results of calculations of the mobility and the effective charge of the melt ions are presented.

Solidification of liquating silicate magmatic melts may lead to formation of rare earth mineral deposits. By the example of quasi-binary system SiO₂–Sc₂O₃, the processes of cooling and directional solidification of the melt in an intrusive chamber have been studied, and velocities of the phase fronts and the width of the phase separation field have been calculated. Using the fluctuation approach, the physical and mathematical model of the formation and growth of dispersed phase in the continuous cooling of liquating melt was developed, and the conditions of incorporating the dispersed inclu-sions by solidified matrix phase were determined. The proposed model allows obtain-ing quantitative estimates of the size and number of inclusions per unit of hardened rock, depending on the solidification conditions and the initial chemical composition of the melt.