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Thermophysics and Aeromechanics

2012 year, number 2

Flow diagnostics downstream of a tribladed rotor model

I.V. Naumov1, V.V. Rahmanov1, V.L. Okulov2, C.M. Velte3, K.E. Meyer3, R.F. Mikkelsen3
1 Kutateladze Institute of Thermophysics SB RAS; Novosibirsk State University
2 Kutateladze Institute of Thermophysics SB RAS; The Technical University of Denmark
3 The Technical University of Denmark
Keywords: rotor systems, helical vortices, vortex wake, Stereoscopic Particle Image Velocimetry
Pages: 171-181

Abstract >>
This paper presents results of a study of vortex wake structures and measurements of instantaneous 3D velocity fields downstream of a triblade turbine model. Two operation modes of flow around the rotor with different tip speed ratios were tested. Initially the wake structures were visualized and subsequently quanti-tative data were recorded through velocity field restoration from particle tracks using a stereo PIV system.
The study supplied flow diagnostics and recovered the instantaneous 3D velocity fields in the longitudinal cross section behind a tribladed rotor at different values of tip speed ratio. This set of data provided a basis for testing and validating assumptions and hypothesis regarding classical theories of rotors.

Dissipation of vortex disturbances in a vibrationally nonequilibrium diatomic gas

YU.N. Grigor'ev1, I.V. Ershov2
1 Institute of Computational Technologies SB RAS
2 Institute of Computational Technologies SB RAS; Novosibirsk State University of Civil Engineering,
Keywords: Kelvin-Helmholtz instability, vibrational relaxation, kinetic energy of disturbances, dissipation
Pages: 183-192

Abstract >>
The influence of the vibrational relaxation on suppression of the Kelvin-Helmholtz instability in an evolving shear layer of a vibrationally nonequilibrium diatomic gas is studied numerically on the basis of equations of two-temperature aerohydrodynamics. Planar waves with the maximum growth rates, which were computed within the framework of a linearized system of equations of inviscid two-temperature gas dynamics, are used as the initial disturbances. It is shown that relaxation of the nonequilibrium vibrational mode at excitation levels, which can be obtained in diatomic gases in nozzle flows, in underexpanded jets, or in flows with moderate laser pumping, is accompanied by noticeable suppression of vortex disturbances. The associated relative enhancement of dissipation of kinetic energy of a large vortex structure averaged over its lifetime reaches approximately 13 %.

Influence of the Prandtl and Knudsen numbers on heat-transfer process in the problem of planar Poiseuille flow

V.N. Popov, D.A. Rudny
Northern (Arctic) Federal University
Keywords: Boltzmann equation, model kinetic equations, models of boundary conditions, gas flow in planar channel, Prandtl number, Knudsen number
Pages: 193-200

Abstract >>
The analytic solution (in the form of the Neumann series) has been derived for the problem of computing the heat flux in a planar channel in the presence of a pressure gradient parallel with the walls (in the problem of planar Poiseuille flow) within the framework of the kinetic approach for arbitrary values of the Prandtl number. The ellipsoidal-statistical model of the Boltzmann kinetic equation is used as the governing equation, and the model of diffuse reflection is used as the boundary condition. The conducted numerical analysis of final expressions obtained in the present work showed a substantial dependence of the heat flux on the value of the Prandtl number of gas for channels whose thickness is comparable with the mean free path of gas molecules.

Effect of mesh screens on the wave drag of a blunt body in supersonic flow

S.G. Mironov1, K.M. Serdyuk2
1 Khristianovich Institute of Theoretical and Applied Mechanics SB RAS; Novosibirsk State University
2 Khristianovich Institute of Theoretical and Applied Mechanics SB RAS,
Keywords: supersonic flows, advanced flat mesh screens, wave drag
Pages: 201-208

Abstract >>
Results of an experimental study of the effect of flat mesh screens on the wave drag of a cylinder with flat face longitudinally streamlined with supersonic airflow at Mach number М = 4.85 are reported. Data on reducing the drag by meshes of various geometries and transparencies installed ahead of the cylinder face were obtained. Weighing and pneumometric measurements, and also PIV measurements of the vector velocity field, are reported. The flow pattern in the vicinity of the cylinder/screen system is visualized. It is shown possible to achieve a substantial (up to 45 %) reduction of the wave drag of the cylinder with a mesh screen. A physical interpretation to the wave-drag reduction phenomenon is given.

Stability and three-wave interaction of disturbances in supersonic boundary layer with mass exchange on the wall

S.A. Gaponov, N.M. Terekhova
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: supersonic boundary layer, hydrodynamic stability, laminar-turbulent transition
Pages: 209-223

Abstract >>
The interaction of disturbances in a boundary layer of the compressible gas is considered in the linear and nonlinear approximation (the weakly nonlinear theory of stability) in the presence of mass exchange (gas blowing or suction) on the surface. The regimes of moderate (the Mach number М = 2) and high (М = 5.35) supersonic velocities of the flow are considered. The suction from the surface is shown to lead to a considerable variation of the linear evolution of disturbances: the vortex disturbances of the first mode and the acoustic disturbances of the second mode are stabilized, the rate of variation is determined by suction intensity. The nonlinear interactions in three-wave systems between the vortex waves in asymmetric triplets at М = 2 and between the waves of different nature (acoustic and vortex waves) ⎯ in the symmetric ones at М = 5.35 are considered. The planar acoustic wave is the excitation wave in the latter, which excites the three-dimensional subharmonic components of the vortex nature. It is shown that one can delay considerably the transition region with the aid of suction, thereby one can reduce the skin-friction drag. In the gas blowing regime, strong deformations of the mean fields of boundary layers occur, which lead to the destabilization of the vortex and acoustic waves in the linear region and activate the nonlinear processes in transition region. One can expect that this will lead to the acceleration of tripping in supersonic flow.

Conical separation zone formation at impingement of supersonic jet on obstacle under cold spraying

A.P. Alkhimov, V.F. Kosarev, S.V. Klinkov, A.A. Sova, G.V. Trubacheev, V.N. Zaikovsky
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: supersonic jet, conical separation zone, cold gasdynamic spraying
Pages: 225-232

Abstract >>
Impingement of supersonic jet upon substrate surface, in front of which conical separation zone is created artificially with the aid of a spike or particle under conditions typical of cold spraying on geometric and dynamic parameters, is considered. Numerical simulation is carried out. Simulation results are in qualitative agreement with experimental observation data. Preliminary analysis of obtained pattern of supersonic jet impingement shows that in local ring area, creation of more favorable conditions for cold spraying of fine particles sized 1 micron or less is possible comparing to typical conditions.

On classification of flow regimes in a channel with sudden expansion

P.V. Bulat1, O.N. Zasuhin2, V.N. Uskov2
1 VNH-Project SEC Mechanics
2 Baltiysky State Technical University Voenmech
Keywords: bottom pressure, bottom region, flow regimes, non-stationary processes
Pages: 233-246

Abstract >>
Supersonic flows of gas in the vicinity of the bottom region known as flows with sudden expansion have been considered. On the basis of extensive experimental studies, authors have proposed a complete classification of flow regimes: stationary, oscillating, and transient. Hysteresis of the regimes change at total gas pressure increasing and decreasing in front of the nozzle has been found. Typical shock-wave configurations emerging at the jet flowing in a channel at different modes have been determined. The type of shock-wave structure and the nature of interaction of the mixing layer of a jet with the wall or reverse flow flowing into the channel from ambient medium determine the appropriate mode. Combination of physical and numerical experiment with bottom pressure calculation according to the developed semi-empirical model have revealed new flow regimes that were not studied earlier.

Wind-tunnel simulation of thick turbulent boundary layer

V.I. Kornilov, A.V. Boiko
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: simulation, incompressible turbulent boundary layer, flat plate, turbulators
Pages: 247-258

Abstract >>
An experimental study aimed at revealing the possibility of simulation, in a subsonic wind tunnel, of enhanced Reynolds numbers Re** via modeling a thick flat-plate boundary layer possessing the properties of a Clauser-equilibrium shear flow is reported. We show that turbulators prepared in the form of variable-height cylinders of height h and diameter d = 3 mm and installed in two rows along the normal to the streamlined wall offer rather an efficient means for modification of turbulent boundary layer in solving the problem. In the majority of cases, mean and fluctuating characteristics of the boundary layer exhibit values typical of naturally developing turbulent boundary layers at a distance of 530 cylinder diameters. The profiles of mean velocity with artificially enhanced boundary-layer thickness can be well approximated, in the law-of-the-wall variables, with the well-known distribution of velocities for canonical boundary layer.

Evolution of kinematic structure of the flow behind a transverse rib for transitional flow regimes

О.А. Dushina, V.M. Molochnikov, N.I. Mikheev, A.A. Paerely
Research Centre for Power Engineering Problems
Keywords: flow visualization, laminar-turbulent transition, large-scale vortex structures, dynamics of kinematic structure of a flow, transverse rib
Pages: 259-266

Abstract >>
Results are presented on visualization of a separated flow behind two kinds of transverse ribs in a channel for a range of Reynolds numbers covering the different stages of laminar-turbulent flow transition. The data was obtained on dynamics of kinematic structure of flow and on evolution of large-scale transverse vortex structures which were generated in the mixing layer during late stages of laminar-turbulent transition. The qualitative estimates were obtained for the vortex generation frequency and velocity of their convective transfer. The features of flow structure were identified for flow behind tested shapes of ribs.

Calculation of critical regimes in the ejectors with converging chamber

A.V. Sobolev
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: gas- and vapor-driven ejectors, real gases, condensation, critical regimes, calculation characteristics
Pages: 267-277

Abstract >>
The calculation procedure of the ejector with water-vapor condensation in primary nozzle and in converging chamber is presented. Calculations are performed in a wide range of temperatures of primary and secondary gases. The differences are identified in the properties of gas- and vapor-driven ejectors. Limiting mass rates ratios of gas ejectors are reached by primary temperature increase, but the highest performance of vapor-driven ejectors is realized with the use of saturated vapor.

Stability of 3D flow of viscous liquid streamlined by the turbulent gas flow

S.P. Aktershev, S.V. Alekseenko
Kutateladze Institute of Thermophysics SB RAS
Keywords: liquid film, 3D flow, turbulent gas flow, stability, waves on the interface
Pages: 279-292

Abstract >>
Stability of the combined flow of liquid film and turbulent gas is studied theoretically for an arbitrary angle between the directions of gas flow and gravity force. The three-dimensional wave flow of the film is described on the basis of integral approach and quasilaminar model of the turbulent gas flow. Increment and phase velocity of waves are calculated for the case of a vertical film and horizontal gas flow depending on the direction of their propagation. According to calculations, the cross gas flow increases the instability area significantly as well as the range of directions for propagation of the fast growing perturbations on the film surface.

Nonstationary periodic spatial waves on the surface of a viscous liquid film falling down a vertical cylinder

O.YU. Tsvelodub1, A.A. Bocharov2
1 Novosibirsk State University; Kutateladze Institute of Thermophysics SB RAS
2 Rzhanov Institute of Semiconductor Physics SB RAS
Keywords: falling film, vertical cylinder, model equation, evolution, 3D perturbations, families of solutions
Pages: 293-306

Abstract >>
The flows of viscous liquid film over the outer surface of a vertical cylinder are examined. Investigation of wave regimes in the case of low flow rates and large cylinder radii is reduced to the analysis of solutions to a nonlinear evolution equation for the film thickness. There are countable numbers of steady-state traveling solution families in the considered model. In turn, most of them are unstable to 2D and 3D perturbations. Thus, evolution of initial perturbations in different ranges of parameter values differs significantly.
Some typical scenarios of perturbation development are presented in this work. Initial perturbations with some symmetries, kept in the process of evolution, are of a particular interest. In these cases, solutions are drawn up to the steady-state traveling solutions with similar symmetry.

The features of rewetting dynamics of the overheated surface by a falling film of cryogenic liquid

I.P. Starodubtseva, A.N. Pavlenko, O.A. Volodin, A.S. Surtaev
Kutateladze Institute of Thermophysics SB RAS
Keywords: transitional processes, film flow, liquid nitrogen, numerical modeling
Pages: 307-316

Abstract >>
The dynamic process of rewetting of the overheated surface by gravitationally falling film of cryogenic liquid was firstly modeled numerically with consideration of local distribution of heat transfer coefficient in the wetting zone along the 2D front. The front shape corresponding to self-organizing regular structures observed in experiments was obtained in the numerical experiment. Evolution of the front shape was studied. It was shown that local motion velocities of different areas of the 2D wetting front differed significantly. Total time of transitional process was determined by the minimal velocity of evaporating liquid boundaries in the front zones between boiling jets. This model allows quantitative determination for the wetting front velocity, variable in time and space, and temperature fields in the heater. Reliability of calculation results was proved by direct comparison with experimental data.

Numerical simulation of natural convection in a sessile liquid droplet

M.V. Bartashevich, I.V. Marchuk, O.A. Kabov
Kutateladze Institute of Thermophysics SB RAS
Keywords: sessile droplet, convective heat transfer, thermal convection
Pages: 317-328

Abstract >>
Heat transfer in a sessile liquid droplet was studied with numerical methods. A computer code was developed for solving the problem of convection in an axisymmetric hemispherical droplet and in a spherical layer as well. The problem of establishing an equilibrium state in a droplet was solved using several variables: temperature, stream function, and vorticity. Simulation was performed for droplets of water, ethyl alcohol, and model liquids. Variable parameters: intensity of heat transfer from droplet surface, Rayleigh and Marangoni dimensionless criteria, and the characteristic temperature difference. It was revealed that the curve of convective flow intensity versus heat transfer intensity at droplet surface has a maximum. A dual-vortex structure was obtained in a stationary hemispherical profile of liquid droplet for the case of close values for thermocapillary and thermogravitational forces. Either thermocapillary or thermogravitational vortex might be dominating phenomena in the flow structure.

Transient behavior of superheated water jets boiling

A.V. Reshetnikov, K.A. Busov, N.A. Mazheiko, V.N. Skokov, V.P. Koverda
Institute of Thermophysics UB RAS
Keywords: superheated liquid, nucleation frequency, transient behavior of boiling, jet forms, 1/f fluctuations
Pages: 329-336

Abstract >>
Superheated water flowing out from high-pressure chamber through short cylindrical and slot channel has been studied experimentally. Relation of vaporization mechanisms in superheated liquid (boiling in single, not interacting centers, intense heterogeneous vaporization, and homogeneous fluctuating nucleation) and respective forms of superheated water jets has been determined. Temperature intervals with transient behavior of boiling have been determined. It is shown that at transient behavior of boiling the amplitude of pulsations of jet parameters increases, and in the spectra of pulsation power, the low-frequency component 1/f appears.

Evaluating partial pressure of vapors for various oxides

D.YU. Trufanov, A.P. Zavyalov, V.I. Lysenko, S.P. Bardakhanov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: partial pressure, oxides
Pages: 337-342

Abstract >>
To improve control of the process of nano-powder production in the industrial plant based on electron accelerator, partial pressure of vapors was evaluated at evaporation for different reactions of aluminum, silicon, and titanium oxides. The performed experiments qualitatively proved the correctness of calculations. Besides, influence of water vapors added in gas-carrier on the productivity and average size of the particles of the obtained nano-powder were studied experimentally.

Temperature and concentration dependences of thermal conductivity of solid solutions of gadolinium and dysprosium sulfides

S.M. Luguev1, N.V. Lugueva1, V.V. Sokolov2
1 Amirkhanov Institute of Physics DSC RAS
2 Nikolaev Institute of Inorganic Chemistry SB RAS
Keywords: thermal conductivity, sulfides of gadolinium and dysprosium
Pages: 343-348

Abstract >>
Thermal conductivity of a number of solid solutions of gadolinium and dysprosium sulfides has been studied experimentally within the temperature range 80−400 K. The work offers the data on thermal conductivity coefficient and lattice thermal conductivity of the studied samples. It was found that replacement of gadolinium ions by dysprosium ions leads to significant decrease of the samples' thermal conductivity and changes its temperature dependence character due to the resonance scattering of phonons by paramagnetic ions of dysprosium. Influence of this mechanism of phonon scattering conditions the area of anomalous change observed on the concentration dependence of thermal conductivity coefficient.

75th Anniversary of Eduard P. Volchkov

Editorial board
Siberian Branch of the RAS
Pages: 349-350

Abstract >>
On May 6, 2012 Eduard P. Volchkov, the prominent scientist working in the area of thermophysics, Doctor of Technical Sciences, Professor, and Full Member of the Russian Academy of Sciences became 75 years of age.