


Vol 54, No 1 (2019)
- Year: 2019
- Articles: 12
- URL: https://journals.rcsi.science/0015-4628/issue/view/9464
Article
Separation of Low-Melting Metal Melts in a Thin Inclined Capillary
Abstract
Direct numerical simulation of the process of separation of binary low-melting metal melts in a thin nonuniformly heated inclined capillary is carried out. A physical model which describes the macroscopic motion in the melt and the process of separation of the liquid mixture in components is constructed on the basis of laws and equations valid for the multiphase hydrodynamic systems. The calculation results are compared with the experimental data. The separation time is compared for various angles of inclination of the layer, the characteristic concentration fork which demonstrates separation dynamics is reproduced, and the qualitative agreement with the experiment is obtained for the component concentrations in the cross-section. In the course of numerical simulation, that replicates the succession of experimental actions with the maximum precision, the presence of the specific maximum for the difference between the end-face concentrations at a certain angle of inclination of the channel is confirmed. The radical difference between the calculation results obtained within the framework of the model considered and the conclusions made earlier in explanation of the experiment by other authors is demonstrated.



Wave Motion in an Ice Sheet with Crack under Uniformly Moving Load
Abstract
The analytical solution to the problem of the behavior of an ice sheet with rectilinear crack under the action of uniformly moving rectangular external pressure zone simulating an air-cushion vehicle is obtained using the Wiener–Hopf technique. The ice cover is simulated by thin elastic semi-infinite plates of constant thickness floating on the surface of an incompressible fluid of finite depth. Two configurations are considered: 1) two semi-infinite plates with free edges (whose thicknesses can be different) are separated by a crack; 2) fluid is bounded by the vertical wall and the ice cover edge can be both free and frozen to the wall. In the case of the contact of plates of the same thickness, as well as in the presence of the wall, the solution is obtained in the explicit form. It is shown that in the case of the contact of identical plates with free edges, edge waveguide modes traveling along the crack are excited when the load moves at a supercritical speed. Both the wave forces acting on the moving body and the deflections of the plates are investigated for various values of the plate thicknesses and the load velocity in the sub- and supercritical regimes.



Two-Dimensional Plane Steady-State Thermocapillary Flow
Abstract
The problem of a two-dimensional steady flow of a fluid in a flat channel with a free boundary when the surface tension coefficient depends linearly on the temperature is considered. On the channel bottom, a fixed temperature distribution is maintained. The temperature in the fluid is distributed in accordance with the quadratic law, which is consistent with the velocity field of the Xiemenz type. The arising boundary-value problem is strongly nonlinear and inverse with respect to the pressure gradient along the channel. The application of the tau-method shows that this problem has three different solutions. In the case of a thermally insulated free boundary, only one solution exists. Typical flow patterns are studied for each solution.



Analysis of the Shape Hysteresis of a Soap Film Supported by Two Circular Rings
Abstract
The behavior of a minimal surface supported by two circular coaxial rings is analyzed by increasing (decreasing) distance between rings. The assumption on metastability of certain configurations of the minimal surface is confirmed. This makes it possible to explain hysteresis of a soap film taking on different configurations observed experimentally. The effectiveness of applying analytical methods of the theory of flows of Non-Newtonian fluids through porous media to the problem of describing minimal surfaces on rings is demonstrated.



Exact Solution of the Equations of Axisymmetric Viscous Fluid Flow between Parallel Plates Approaching and Moving Apart from One Another
Abstract
The exact solutions of the Navier-Stokes equations in a fluid layer in between parallel plates moving so that the distance varies in accordance with an arbitrary-power law are investigated. The no-slip condition is imposed on the plate boundary. The exact solutions of the Navier-Stokes equations are constructed as series in powers of the Reynolds number. The cases of the decelerated motion in accordance with the time-square-root law, the uniform motion, and the uniformly accelerated motion of the plates are studied in detail. In the first of the cases mentioned above the series converge and in the other cases the solution is determined by means of asymptotic series. The critical Reynolds number which corresponds to the development of backflow is determined.



Laminarization of Flow with Heat Transfer in a Plane Channel with a Confuser
Abstract
The process of laminarization of turbulent flow with heat transfer in a plane confuser with a constant constriction angle is numerically simulated. The effect of the favorable longitudinal pressure gradient on the flow and heat transfer parameters is shown. The results of the calculations are compared with the experimental data on the heat transfer. The value of the acceleration parameter, at which flow in the channel becomes fully laminar, is determined.



Control of Flow Past a Model Aircraft in the Landing Configuration Using Aerodynamic Strakes
Abstract
The results of numerical investigation of a simplified model of the civil aircraft layout in the landing regime are presented. Numerical simulation is performed within the framework of the Reynolds equations. The aerodynamic characteristics of the model are studied in the case in which the flow is controlled by means of mounting strakes (vortex generators) on the nacelle and the fuselage. It is shown that mounting simultaneously the two strakes leads to a considerable increase in the maximum lift of the layout, while in the case in which only one fence is mounted on either the nacelle or the fuselage it increases only slightly.



Problem of Deep Bed Filtration in a Porous Medium with the Initial Deposit
Abstract
The macroscopic model of long-term deep-bed filtration flow of a monodisperse suspension through a porous medium with size-exclusion particle-capture mechanism and without retained-particle mobilization is considered. It is assumed that the pore accessibility and the fractional particle flux depend on the deposit concentration and at the initial time the porous medium contains a nonuniformly distributed deposit. The aim of the study is to find the analytical solution in the neighborhood of a mobile curvilinear boundary, namely, of the suspended-particle concentration front. The property of having fixed sign is proved for the solution. The exact solution of the filtration problem on the curvilinear front is found in explicit form. The sufficient condition of existence of the solution on the concentration front is obtained. An asymptotic solution is constructed in the neighborhood of the front. The time interval of applicability of asymptotics is determined from the numerical solution.



Calculation of Nonequilibrium Radiation of Shock Waves in the Air Using Two Models
Abstract
The results of the numerical modeling of the spectral radiating capacity of shock-wave-heated air are presented. Two models of nonequilibrium radiation emitted from the relaxation zone behind the strong shock wave front are used. The first model is based on Euler equations and formulated for the one-dimensional problem of kinetic processes behind the shock front. The second model is based on the two-dimensional Navier-Stokes equations for a viscous shock layer on the nose surface of a blunt body in a hypersonic flow. The problem of the interpretation of the Fire-II flight experiment are discussed using the above-mentioned models.



RANS/ILES Analysis of the Flow Pattern and the Acoustic Characteristics of a Supersonic Off-Design Jet at Large Nozzle Pressure Ratios
Abstract
The outflow of a cold supersonic off-design jet with the nozzle pressure ratio of 21.8 is calculated using the high-resolution RANS/ILES method. For the nozzle under consideration and at the given nozzle pressure ratio the exit-to-ambient pressure ratio is 0.6. The jet is characterized by a long supersonic region with many “barrels.” The calculations are validated against the experimental data. The fluctuating and acoustic characteristics of the jet flow under consideration are compared with the characteristics of other supersonic jets. The geometric dimensions of the barrels and the acoustic properties of the jet are estimated from the known empirical relations for supersonic jets.



Effect of Sudden Expansion on Two-Phase Flow in a Horizontal Pipe
Abstract
This paper presents an experimental investigation of two-phase liquid-gas flow across a sudden expanded diameter in a horizontal pipe. A closed flow loop having a transparent pipe was designed and constructed to investigate the dynamics of slug flow at the sudden expanded area. Using High Speed Photography, the horizontal water jet characteristics were investigated for both single and two-phase flow. Bubble velocity in expanded region is quantified and depends strongly on both liquid and gas flowrates. Using image analysis, the bubble burst phenomenon is described and liquid film thickness is estimated. The flow regime map and corresponding flow patterns in expanded area are established. The measurements presented in this study provide fundamental insights into the influence of the sudden expansion on two phase liquid-gas flow behaviors.



Eddy Viscosity and Velocity Profiles in Fully-Developed Turbulent Channel Flows
Abstract
In this study, we present eddy viscosity formulations based on analytical solutions for turbulent kinetic energy (TKE) in fully-developed turbulent channel flows. Mean streamwise velocities are obtained by solving the momentum equation with the proposed analytical eddy viscosity formulations. Our results were validated by comparisons with DNS data of fully-developed turbulent channel flows for 300 < Reτ < 2000 (where Reτ denotes the friction Reynolds number defined by the friction velocity uτ, kinematic viscosity ν and the channel half-width δ). Our method allows accurate description of mean streamwise velocity profiles and turbulent shear stress outside the log-law layer, in the viscous and buffer layers and in the outer region. The aim of this study is to provide simple analytical tools for turbulent channel flow applications.


