Home – Home – Jornals – Thermophysics and Aeromechanics 2015 number 3

The review deals with the analysis of the factors affecting the boundaries of two-phase regimes in the channels of different cross sections, whose minimal size is less than the capillary constant. The channels are classified by size. Data for two-phase flow regimes are systematized and summarized in tables for the round and rectangular tubes. It is indicated that the most studies identify the following two-phase flow regimes: bubble, slug and annular. The regimes found in some papers are described. The terminology used to describe the regimes is kept. Here we analyze the main factors affecting the structure of the two-phase flow, such as gas and liquid flow rates, parameters of the channel and input section, wettability of the inner surface of channels, liquid properties, and gravitational forces. It is shown that development of instability of the two-phase flow has a significant impact on formation, evolution, and change of the flow regimes.

The Landau problem on the evaporation front stability is generalized to the case of finite thickness of the evaporating liquid layer. The analysis of the influence of additional factors, the impermeability condition of solid wall and resulting pulsations of mass velocity, is carried out. Parametric calculations of the stability boundary are performed when changing the liquid film thickness and the relationship between phase densities in the framework of asymptotic Landau approach for the Reynolds number Re > 1. Approximate evaluation of the influence of liquid viscosity on the stability boundary has been done.

The algorithms of solution to the Young–Laplace equation, describing the shape of an axisymmetric droplet on a flat horizontal surface, with various ways of setting the initial data and geometric parameters of a droplet, were derived and tested. Analysis of the Young–Laplace equation showed that a family of curves that form the droplet surface is the single-parametric one with the accuracy of up to the scale factor, whose role is played by the capillary length, and the contact angle determines the curve turn at a contact point, but it does not affect the shape of the curve. The main natural parameter defining the family of the forming curve is the curvature at the droplet top. The droplet shape is uniquely determined by three independent geometric parameters. This fact allows us to calculate the physical properties, such as the capillary length and contact angle, measuring three independent values: height, droplet diameter, and diameter of the droplet base or the area of the axial cross section of the droplet or its volume.

Numerical simulation of the flow of an aerosol of polydisperse composition in a plane duct, where the resonance acoustic oscillations are generated, which are directed across the flow, has been carried out. The peculiarities of the flow, which is followed by coagulation and alteration of the distribution of particles over their sizes, have been described. The carrying medium has been modeled with the aid of the system of NavierStokes equations for compres-sible heat-conducting gas. The polydisperse phase dynamics is described by the systems of equations involving the equations of continuity, conservation of the momentum and internal energy. Equations of the motion of carrying medium and disperse fractions are written with allowance for interphase exchange by the momentum and energy. A Lagrangian model has been used to describe the coagulation process. The dispersion alteration in the gas-particle flow under the action of acoustic oscillations, which are resonant for the duct cross section, is analyzed.

The thermoacoustic effect concerns conversion of energy between a gas and a solid in the presence of acoustic waves. Although the working principle is well understood, the optimal design of thermoacoustic devices remains a challenge. The present work aims to perform a numerical simulation of a simple standing-wave thermoacoustic device. The analysis of the flow and the prediction of the heat transfer are performed by solving the non-linear unsteady Navier–Stokes equations using the finite volume method implemented in the commercial code ANSYS-CFX. The goal of this work is to study the effect of the stack temperature gradient, on the acoustic pressure and the produced acoustic power. This stack temperature gradient generates the thermoacoustic instability in standing-wave thermoacoustic resonator. The obtained results show an increase of the acoustic pressure and the acoustic power while increasing in the stack temperature gradient. The thermodynamic cycles of the thermoacoustic device are illustrated and observed for the different stack temperature gradients.

An experimental study of the structure of a pulsating air flow through a smooth channel was carried out. The flow pulsations were artificially imposed onto the main flow through periodic blockage of channel outlet cross section. A method for determining the additional shear stresses due to the imposed flow pulsations is proposed. The essence of the method consists in the determination of the shear stresses based on the revealed dynamics of the flow velocity field, whose measurements were carried out by the optical method from the results of digital video recording of the flow pattern. Profiles of velocities, accelerations, and additional shear stresses during a period of imposed flow pulsations were obtained.

Results of a numerical study of the thermal effectiveness of a gas wall screen implemented via gas blowing through cylindrical inclined holes embedded in a transverse trench are reported. The calculations were performed using 3D Reynolds-averaged Navier–Stokes equations, with the flow turbulence being modeled by means of the Reynolds-stress model. Blowing into the trench was compared to the conventional cooling technique using gas blowing without a trench. The film cooling effectiveness with gas injection through circular holes embedded in trench exceeds significantly the effectiveness of blowing without a trench. Such a method of coolant supply into the flow proved to be especially advantageous at high blowing ratios. Due to the formation of vortical structures inside the trench, a more uniform cooling flow in the spanwise direction can be achieved. A comparative analysis is indicative of acceptable qualitative agreement of the experimental and predicted data.

The plane oscillations of the elliptic cavity filled with a viscous incompressible liquid have been investigated numerically. Characteristic decay time depending on the values of system parameters has been determined, the values of parameters at which this time is minimum have been found. Flow patterns of liquid in the cavity are presented.

The density and thermal expansion coefficients of liquid potassium–lead alloys (30.01, 39.99, 50.00, 66.66, 84.40, and 90.70 at. % Pb) have been determined using gamma-ray attenuation technique over the temperature range from liquidus line to 975 K. The experimental uncertainty of the density measurement is estimated to be within ±0.2–0.4 %. A comparison of the obtained results with literature data has been made. Temperature and concentration dependences of the volumetric properties of liquid K–Pb system have been built and analyzed.

The flow around a model in the closed test section of a low-speed wind tunnel has been analyzed in 2D approximation. As the contour of the nozzle, test section, and diffuser, the contour of the T-324 wind tunnel, of the Khristianovich Institute of Theoretical and Applied Mechanics (ITAM SB RAS, Novosibirsk), in its symmetry plane was adopted. A comparison of experimental with calculated data on the distribution of velocities and dynamic pressures in the test section is given. The effect due to the sizes of a model installed in the test section on the values of the aerodynamic coefficients of the model is analyzed. As the aerodynamic model, the NASA0012 airfoil and the circular cylinder were considered. For the airfoil chord length b = 20 % of nozzle height, the values of the aerodynamic coefficients of the airfoil in the free stream and in the test section proved to be close to each other up to the angle of attack α = 7°, which configuration corresponds to blockage-factor value ξ ≈ 7 %. The obtained data are indicative of the expedience of taking into account, in choosing the model scale, not only the degree of flow passage area blockage by the model but, also, the length of the well-streamlined model. In the case of a strongly blunted body with a high drag-coefficient value, the admissible blockage factor ξ may reach a value of 10 %.

The paper formulates the issue of development of experimental base with noninvasive optical-electronic tools for control of combustion in a combustion chamber of gas turbine engine. The design and specifications of a pilot sample of optronic system are explained; this noninvasive system was created in the framework of project of development of main critical technologies for designing of aviation gas turbine engine PD-14. The testbench run data are presented.

The work presents a method of complex investigation of thermal radiation emitted by heterogeneous combustion products in the model rocket engine plume. Realization of the method has allowed us to obtain full information on the results in all stages of calculations. Dependence of the optical properties (complex refractive index), the radiation characteristics (coefficients and cross sections) and emission characteristics (flux densities, emissivity factors) of the main determining factors and parameters was analyzed. It was found by the method of computational experiment that the presence of the gaseous phase in the combustion products causes a strongly marked selectivity of emission, due to which the use of gray approximation in the calculation of thermal radiation is unnecessary. The influence of the optical properties, mass fraction, the function of particle size distribution, and the temperature of combustion products on thermal radiation in the model rocket engine plume was investigated. The role of "spotlight" effect – increa-sing the amount of energy of emission exhaust combustion products due to scattering by condensate particles radiation from the combustion chamber – was established quantitatively.

A mathematical model was developed for accumulation of oil in a cylindrical tank (the dome-separator) designed for capturing of oil from oil leakage at the sea bottom. Two key stages were described, and time dependencies for interface evolution and alcohol layer temperature were calculated.

On June 17, 2015 Robert I. Nigmatulin, the prominent scientist specialized in mechanics and mathematics, academician of the Russian Academy of Science became 75 years of age.

On June 26, 2015 Professor Anatoliy P. Burdukov, Doctor of Technical Sciences, the Laureate of the State Prize in Science and Engineering, the Honored Worker of Russian Science, became 80 years of age.