Home – Home – Jornals – Thermophysics and Aeromechanics 2013 number 2

A new phenomenon of the spontaneous development of the rotating inertial gravity wave inside the rigid cylindrical tank has been observed. The experimental set-up combines both the inflow and outflow. Three regimes of the flow inside the tank have been disclosed for the fixed rate of the liquid height change: a) nonrotating flow, b) nonrotating flow with the ripple localized to the tank’s wall, and c) emergence of the rotating inertial gravity wave. The rotating inertial gravity wave forces the fluid to rotate in the opposite direction. Each of these regimes is realized in some ranges of the outlet diameters and liquid heights, and the maps of these regimes are established.

The improved numerical models based on the algebraic representations of the Reynolds stresses and fluxes and the use of the differential equation for the transfer of the dispersion of fluctuations of the vertical velocity component are considered for describing the processes of a vertical turbulent exchange in a stably stratified reservoir. Numerical model-ling of the penetration of a turbulent layer of a mixed fluid in a linearly stratified medium under the action of constant shear stress is carried out. Computational results agree well with known experimental data and point to a substantial influence of the anisotropy of the flow on its main characteristics.

Results of numerical investigation of the flow and heat transfer at turbulent free convection between the vertical parallel isothermal plates with different temperatures are presented. The temperature factor RT varied within –2 ÷ 1. The Rayleigh number changed within Ra = 10⁷ ÷ 10⁹, and the ratio of geometrical sizes of plates and distances between them was constant A = L/w = 10. Numerical studies were performed via the solution to the two-dimensional Navier—Stokes equations and energy equation in Boussinesq approximation. The considered boundary-value problem has the unknown conditions at the inlet and outlet between the plates. To describe turbulence, the modified low-Reynolds k–ε model was used. The effect of the temperature factor on the flow structure at the channel inlet and outlet was analyzed. Data on distributions of velocities and temperatures between the plates, local and integral heat transfer allow deeper understanding of the mechanism of transfer processes between the parallel plates with asymmetrical heating.

Results of a numerical and experimental study of flow-field characteristics in the test section of the Т-313 supersonic blow-down wind tunnel of ITAM SB RAS at Mach number М = 7 are reported. The distributions of local Mach numbers, stagnation temperatures, static pressures, angles of flow deflection from the test-section axis were analyzed. For comparison, distributions of Mach numbers across the flow at several stations at М = 5 and 6 are reported as well. We show that, in the T-313 wind tunnel, two-dimensional nozzle inserts can be used to perform experiments at М = 7.

Results of numerical simulation are discussed: simulation was carried out for a configuration of two wedges with sweepback leading edges placed on a pre-compression ramp in a way that skewed surfaces of the wedges deflect the compressed flows in the opposite directions. It was demonstrated that this configuration produces a flow with irregular interaction in the plane of symmetry for shock waves produced by sweepback wedges. The shock waves formed by the skew wedges induce 3D boundary layer separations along sweepback leading edges of the wedges. Flows in the separation zones are directed toward the plane of symmetry of this configuration; they interact and produce in the central part a “swollen” zone of separation flow with a typical S-shaped profile of velocity. Simulation data was obtained for the free stream flow with Mach number М = 4 and 6 and based upon Navier—Stokes equations and k-ω  SST turbulence model using FLUENT computation code. Inviscid flow described by Euler equations was considered as well.

The engineering calculation method has been developed for investigation of the process of thermal destruction of “Fregat” upper stage at deorbiting and descent into the Earth’s atmosphere. The results of calculation of its descent trajectory and characteristics of aerodynamic heating are presented. Within the framework of the thermodynamic approach, the authors investigated the process of pressure increase in the tanks due to heating and evaporation of the liquid phase of fuel. Stresses in the shells, the height and the energy equivalent of explosive destruction of tanks were calculated depending on the degree of their filling with remains of the components of liquid fuel.

Modelling results on characteristics of the cooling system, which combines the Peltier element with the radiator-emitter, are presented in the paper. Despite wide application of Peltier elements, characteristics of this system are hardly studied since there are no such combinations under the terrestrial conditions. The necessity to study the parameters of this combined cooler arose because such systems are planned to be used for thermal stabilization of detectors in the promising space telescope ART-XC, used at the Russian-German observatory “Spectrum-RG” and in monitor SPIN-Х1-ASM, which will be installed at the International Space Station (ISS). According to modelling, the cooler consisting of the Peltier element and radiator-emitter has some unusual properties caused by the complex feedback between these units.

The density and thermal expansion coefficients of liquid sodium and sodium-lead alloys (2.50, 5.00, 7.50, 9.99, and 21.03 at. % Pb) were investigated using gamma-ray attenuation technique in the temperature range from the liquidus line up to 950 K. Accuracy of density measurement is estimated to be ± 0.2–0.4 %. Temperature and concentration dependences of thermal properties of liquid system Na–Pb have been built.

The work is devoted to the mathematical modelling and numerical solution of the problems of conjugate micro-convection, which arises under the laser radiation action in the metal melt with surface-active refractory disperse components added for the modification, hardening, and doping of the treated surface. A multi-vortex structure of the melt flow has been obtained, the number of vortices in which depends on the surface tension variation, on the temperature and power of laser radiation. Special attention is paid to the numerical modelling of the behavior in the melt of the substrate of disperse admixture consisting of the tungsten carbide particles. The role of microconvection in the distribution of powder particles in the surface layer of the substrate after its cooling is shown.

A mathematical model is formulated to describe thermophysical processes at laser welding of metal plates for the case when the modifying nanoparticles of refractory compounds have been introduced in the weld pool (the nanopowder seed cultrure fermenters — NSCF). Specially prepared nanoparticles of refractory compounds serve the crystallization centers that is they are in fact the exogenous primers, on the surface of which the individual clusters are grouped. Owing to this, one can control the process of the crystallization of the alloy and the formation of its structure and, consequently, the joint weld properties. As an example, we present the results of computing the butt welding of two plates of aluminum alloy and steel. Computed and experimental data are compared.

A physical and mathematical model has been proposed for computing the thermal state and shape of the individual deposited track at the laser powder cladding. A three-dimensional statement of the two-phase problem of Stefan type with curved moving boundaries is considered. One of the boundaries is the melting-crystallization boundary, and the other is the boundary of the deposited layer, where the conservation laws are written from the condition of the inflow of the additional mass and energy. To describe the track shape the equation of kinematic compatibility of the points of a surface is used, the motion of which occurs at the expense of the mass of powder particles supplied to the radiation spot. An explicit finite difference scheme on a rectangular nonuniform grid is used for numerical solution of equations. The computations are carried out by through computation without an explicit identification of curved boundaries by using a modification of the immersed boundary method. The computational results are presented for the thermal state and the shape of the surface of the forming individual track depending on physical parameters: the substrate initial temperature, laser radiation intensity, scanning speed, powder feeding rate, etc.