Novosibirsk, Russia
Novosibirsk, Russia

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This paper is devoted to a theoretical analysis of nonlinear two-dimensional waves using both the Navier-Stokes equations in their full statement and two integral approaches: Shkadov's approach and 'the regularized integral model'. We found the steady-state travelling waves and carried out an analysis of their linear stability and bifurcations using the Floquet theory. We found that thesolutions of the Navier-Stokes equations are qualitatively different from the solutions of Shkadov's integral approach starting from some values of the Kapitza number Ka. It is found that the solutions of all models considered here have an internal vortex at moderate Reynolds numbers Re. A linear stability analysis with respect to the periodic disturbances of the same wavelength L as a period of the nonlinear solution allows us to calculate the bifurcation lines of the nonlinear waves on the plane of two parameters (wavelength L and Re/Ka) for different values of Ka. These lines form a multi-fold and multi-sheet surface where we can compute the different types of solutions at one set of parameters by using the continuation principle and starting the computations with small values of Re/ Ka. We found that most of the solutions are unstable. © 2012 The Japan Society of Fluid Mechanics and IOP Publishing Ltd.

Misyura S.Ya.,RAS Institute of Thermophysics
Chemical Physics Letters | Year: 2013

The dissociation of methane hydrate under external pressure of 1 bar is studied experimentally. Non-isothermal dissociation is fundamentally different from the quasi-isothermal case. The increase in the density of heat flux from 255 to 13 700 W m 2 results in 9-fold increase in the dissociation rate of methane hydrate. Different variations of clathrates dissociation may be observed depending on the heat flux magnitude: (1) without self-preservation (high heat fluxes), (2) a partial self-preservation with one minimum of dissociation rate, and (3) a partial self-preservation with two minimums (low heat fluxes). When describing dissociation kinetics of the spherical granules, it is important to know the time dependence of the ice layer thickness growth. It is shown that not the curvature, but the heat flux value regulates the dissociation rate and the change in diffusion. A drastic change in dissociation rate is caused by a pressure decrease in pores. © 2013 Elsevier B.V. All rights reserved.

The paper is devoted to a theoretical analysis of the linear stability of the viscous liquid film flowing down an inclined wavy surface. The study is based on the Navier-Stokes equations in their full statement. The developed numerical algorithm allows us to compute both the steady state solution of the nonlinear equations and the rates of growing or damping in time of the arbitrary two-dimensional disturbances of the solution which are bounded in space. The wall corrugations have a great influence on the disturbances behaviour. There is a critical Reynolds number Recr when the steady-state viscous flow over an undulated surface becomes unstable. It is found that the value of Recr depends essentially both on the topography parameters and the liquid's physical properties. In the case of the flat plate, the critical Reynolds number depends only on the value of the inclination angle. For different values of the Kapitza number, the inclination angle, and the Reynolds number we obtained the regions of the corrugation's parameters (amplitude and period) where all two-dimensional disturbances decay in time. © 2014 AIP Publishing LLC.

Kondaurova L.,RAS Institute of Thermophysics | Nemirovskii S.K.,RAS Institute of Thermophysics
Physical Review B - Condensed Matter and Materials Physics | Year: 2012

We submit the results of the numerical experiment on the decay of the quantum turbulence in the absence of the normal component of the superfluid helium. Computations were fulfilled inside a fixed domain with the use of the vortex filament method. The purpose of this study was to ascertain the role of the various factors arising in the numerical procedure, such as change in length in the reconnection processes, the procedures regulating the amount of points on the lines, eliminations of very small loops below the space resolution as well as the evaporation of the loops from the volume. We would like to stress that the widely accepted mechanism-a cascadelike transfer of the energy by nonlinear Kelvin waves (and radiation of sound)-was not considered. One of the reasons is that the space resolution along the lines did not allow to detect generation of high harmonics, moreover, particularly to get harmonics, which really radiate sound. In addition, the use of the method assumes that the fluid is incompressible. Numerical simulations have been performed for the cubic domain with transparent walls embedded in an unbounded space, and for a cube with solid smooth walls. Calculations showed that in the case of unlimited space the decay of quantum turbulence caused by the evaporation of vortex loops, which is implemented in a diffusion-like manner. The rate of the attenuation of the vortex line density agrees with the one, predicted by the theory of diffusion of nonuniform vortex tangles. In the case of a cube with solid walls, the main decay is also due to the diffusion of the vortex loops to boundaries. The vortex loops, whose ends glide on a smooth wall, execute the sophisticated motion (especially when they jump from the one face to the other) with many subsequent reconnections. As a result, there appear smaller and smaller loops with a size of few spatial resolutions, which were removed from the calculation. Indirect comparison with the experiments shows that the time of decay agrees with the measured data. © 2012 American Physical Society.

Misyura S.Y.,RAS Institute of Thermophysics
Experimental Thermal and Fluid Science | Year: 2016

Various evaporation regimes were studied experimentally in a wide range of droplet sizes and wall temperatures at a change in thermal-physical and geometrical characteristics of the wall. With the increasing diameter of the wetting spot of a water sample from 1 to 30 mm, the width of the transition region of boiling crisis increases. Dynamics of large droplets boiling is determined not only by wall overheating, but also by the droplet shape. Evaporation of droplets on the surfaces, whose longitudinal dimensions are much larger than the droplet diameter, should take into account free convection of gas and thickness of diffusion boundary layer, which depends on the droplet diameter. Wall surface polishing causes a multiple increase in evaporation time within the transitional boiling region, in contrast to the rough wall. For We≈. 0 and polished surface of the wall, the time of evaporation and Leidenfrost temperature in the transitional boiling region increase many times, in contrast to the rough wall (for high We number the result is opposite). To assess the effect of wall thickness on the rate of evaporation, it is important to consider the ratio of the droplet diameter to the wall thickness, depth of solid wall cooling, ratio of wall thermal conductivity to conductivity of liquid, and values of dimensionless Bio (Bi) and Fourier (Fo) numbers. © 2015 Elsevier Inc.

The article is devoted to a theoretical analysis of counter-current gas-liquid wavy film flow between vertical plates. We consider two-dimensional nonlinear waves on the interface over a wide variation of parameters. The main interest is to analyse the wave structure at the parameter values corresponding to the onset of flooding observed in experiments. We use the Navier-Stokes equations in their full statement to describe the liquid phase hydrodynamics. For the gas phase equations, we use two models: (1) the Navier-Stokes system and (2) the simplified Benjamin-Miles approach where the liquid phase is a small disturbance for the laminar or turbulent gas flow. With the superficial gas velocity increasing and starting from some value of the velocity, the waves demonstrate a rapid decreasing of both the minimal film thickness and the phase wave velocity. We obtain a region of the gas velocity where we have two solutions at one set of the problem parameters and where the flooding takes place. Both the phase wave velocity and the minimal film thickness are positive numbers at such values of the velocity. We calculate the flooding point dependences on the liquid Reynolds number for two different liquids. The wave regime corresponding to the flooding point demonstrates negative u-velocities in the neighbourhood of the interface near the film thickness maximum. At smaller values of the superficial gas velocity, the negative uvelocities take place in the neighbourhood of the film thickness minimum. © 2009 American Institute of Chemical Engineers.

Nemirovskii S.K.,RAS Institute of Thermophysics
Journal of Low Temperature Physics | Year: 2013

A review of various exactly solvable models on the determination of the energy spectra E(k) of 3D-velocity field, induced by chaotic vortex lines is proposed. This problem is closely related to the sacramental question whether a chaotic set of vortex filaments can mimic the real hydrodynamic turbulence. The quantity {v(k)v(-k) can be exactly calculated, provided that we know the probability distribution functional [InlineEquation not available: see fulltext.] of vortex loops configurations. The knowledge of [InlineEquation not available: see fulltext.] is identical to the full solution of the problem of quantum turbulence and, in general, [InlineEquation not available: see fulltext.] is unknown. In the paper we discuss several models allowing to evaluate spectra in the explicit form. This cases include standard vortex configurations such as a straight line, vortex array and ring. Independent chaotic loops of various fractal dimension as well as interacting loops in the thermodynamic equilibrium also permit an analytical solution. We also describe the method of an obtaining the 3D velocity spectrum induced by the straight line perturbed with chaotic 1D Kelvin waves on it. © 2012 Springer Science+Business Media New York.

Novopashin S.A.,RAS Institute of Thermophysics
Journal of Nanoparticle Research | Year: 2010

In situ electron microscope and X-ray investigations of the morphological and phase characteristics of copper nanoparticles encapsulated in a carbon shell were carried out. It was found that oxidation of the copper nanoparticles starts at a temperature of 200 °C. The formation of oxide phases occurs on the surface of the carbon shells, with the Cu2O phase appearing first followed by the formation of the CuO phase. Upon heating to just below its melting point, the copper sublimes resulting in the formation of hollow carbon nanocapsules. Treatment of the initial or oxidized encapsulated copper nanoparticles with nitric acid and annealing can be used to obtain hollow carbon nanocapsules. © 2010 Springer Science+Business Media B.V.

Morozov A.A.,RAS Institute of Thermophysics
Applied Physics A: Materials Science and Processing | Year: 2013

A theoretical study of the time-of-flight (TOF) distributions under pulsed laser ablation has been performed. 2D simulations of pulsed evaporation of atoms into vacuum on the base of the direct simulation Monte Carlo (DSMC) method have been carried out. It is found that for large evaporating spots (when the spot radius exceeds the initial plume length by a factor of five) the TOF distributions practically do not change with the spot radius variation. Moreover, it is shown that such distributions can be obtained from 1D calculations. Thus, in the frames of 1D approach, the TOF distribution is a function only of the number of the evaporated monolayers, but not of the spot radius. The shape of the TOF distribution is shown to strongly depend on the amount of the evaporated matter. Based on the calculated TOF distributions, dependence of the particle kinetic energy on the number of the evaporated monolayers has been obtained. To verify the theoretical results, experimental data on laser ablation of niobium and mercury have been used, which confirm the obtained dependences. The obtained results allow estimating the irradiated surface temperature from the TOF distributions for monatomic neutral gas. © 2012 Springer-Verlag Berlin Heidelberg.

Trifonov Y.Y.,RAS Institute of Thermophysics
International Journal of Multiphase Flow | Year: 2010

This paper is devoted to a theoretical analysis of counter-current gas-liquid wavy film flow between vertical plates. We consider two-dimensional nonlinear waves on the interface over a wide variation of parameters. We use the Navier-Stokes equations in their full statement to describe the liquid phase hydrodynamics. For the gas phase equations, we use the Benjamin-Miles approach where the liquid phase is a small disturbance for the turbulent gas flow. We find a region of the superficial velocity where we have two solutions at one set of the problem parameters and where the flooding takes place. We calculate the flooding dependences on the gas/liquid physical properties, on the liquid Reynolds number and on the distance between the plates. These computations allow us to present the correlation for the onset of flooding that based on the fundamental equations and principles. © 2010 Elsevier Ltd.

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