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Thermophysics and Aeromechanics

2012 year, number 1

Global response of laminar flow separation to local flow perturbations (review)

A.V. Dovgal, B.YU. Zanin, V.V. Kozlov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS,
Keywords: straight wing, massive separation, separation control
Pages: 1-8

Abstract >>
In the present paper, we summarize our experimental data on flow separation control on wings at low subsonic velocities. The focus is on the reduction of the separation region by stationary and nonstationary controlled flow perturbations. Wind-tunnel data obtained for test models of different aspect ratios prove that the entire separated flow can be modified by forcing its narrow parts much smaller in size than the transverse extent of the separation region. Such an approach to flow control at laminar separation comes from non-local interaction of the large-scale flow structure with spatially concentrated disturbances.

Distribution of mean velocity in turbulent boundary layer over permeable surface with air blowing

V.I. Kornilov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: incompressible turbulent boundary layer, permeable wall, microblowing, velocity profile
Pages: 9-16

Abstract >>
In the present article, we investigate the possibility of using simple physical models for predicting properties of incompressible turbulent boundary layer on permeable wall at various values of air-microblowing mass flow rate. It is shown that the velocity scaling Uδ*/δ99 can be successfully used to approximate the distribution of mean velocity in the outer region of the boundary layer. The use of this scaling makes the velocity profiles invariant with respect to Reynolds-number variation; this circumstance largely facilitates the analysis of experimental data, making it independent of upstream flow conditions. The distribution of mean velocity in the logarithmic flow region of the boundary layer over permeable surface can be described with a modified law of the wall involving a constant C0 equal to the same constant for canonical boundary layer, and a quantity K being a weak function of blowing ratio.

Numerical study of shock wave entry and propagation in a microchannel

G.V. Shoev1, YE.A. Bondar1, D.V. Khotyanovsky1, A.N. Kudryavtsev1, K. Maruta2, M.S. Ivanov1
1 Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
2 Tohoku University
Keywords: shock wave propagation, microchannel, Direct Simulation Monte Carlo method, slip and temperature jump, unsteady supersonic microflows
Pages: 17-32

Abstract >>
The entry of a shock wave with the Mach number Mis = 2.03 into a microchannel and its further propagation is numerically studied with the use of kinetic and continuum approaches. Numerical simulations on the basis of the Navier ⎯ Stokes equations and the Direct Simulation Monte Carlo method are performed for different Knudsen numbers Kn = 8·10−3 and 8·10−2 based on the microchannel half-height. At the Knudsen number Kn = 8·10−3, amplification of the shock wave after its entry into the microchannel is observed. Further downstream, the shock wave is attenuated, which is in qualitative agreement with experimental data. It is demonstrated that results predicted by a quasi-one-dimensional model (which ignores viscosity and heat conduction) of shock wave propagation over a channel with an abrupt change in the area agrees with results of numerical simulations on the basis of the Euler equations. In both cases, shock wave acceleration (amplification) after its entry into the microchannel is observed. At the Knudsen number Kn = 8·10−2, the influence of the entrance shape on shock wave propagation over the microchannel is examined. Intense attenuation of the shock wave is observed in three cases: channel with sudden contraction, junction of two channels with an additional thin separating plate, and rounded junction in the form of a sector with an angle of 90° (quarter of a circumference). It is shown that the microchannel entrance shape can affect further propagation of the shock wave. The wave has the highest velocity in the case with a rounded entrance.

Buoyancy-assisted mixed convective flow over backward-facing step in a vertical duct using nanofluids

H.A. Mohammed1, A.A. Al-aswadi2, M.Z. Yusoff2, R. Saidur3
1 University Teknologi Malaysia
2 University Tenaga Nasional
3 University of Malaya
Pages: 33-52

Abstract >>
Laminar mixed convective buoyancy assisting flow through a two-dimensional vertical duct with a backward-facing step using nanofluids as a medium is numerically simulated using finite volume technique. Different types of nanoparticles such as Au, Ag, Al2O3, Cu, CuO, diamond, SiO2 and TiO2 with 5 % volume fraction are used. The wall downstream of the step was maintained at a uniform wall temperature, while the straight wall that forms the other side of the duct was maintained at constant temperature equivalent to the inlet fluid temperature. The walls upstream of the step and the backward-facing step were considered as adiabatic surfaces. The duct has a step height of 4.9 mm and an expansion ratio of 1.942, while the total length in the downstream of the step is 0.5 m. The downstream wall was fixed at uniform wall temperature 0 ≤ ΔT ≤ 30 °С, which was higher than the inlet flow temperature. The Reynolds number in the range of 75 ≤ Re ≤ 225 was considered. It is found that a recirculation region was developed straight behind the backward-facing step which appeared between the edge of the step and few millimeters before the corner which connect the step and the downstream wall. In the few millimeters gap between the recirculation region and the downstream wall, a U-turn flow was developed opposite to the recirculation flow which mixed with the unrecirculated flow and traveled along the channel. Two maximum and one minimum peaks in Nusselt number were developed along the heated downstream wall. It is inferred that Au nanofluid has the highest maximum peaks while diamond nanofluid has the highest minimum peak. Nanofluids with a higher Prandtl number have a higher peak of Nusselt numbers after the separation and the recirculation flow disappeared.
Key words: mixed convection, buoyancy-assisted flow, backward-facing step, nanofluids.

Numerical simulation of thermocapillary convection at surface modification by impulse laser radiation

V.N. Popov, O.B. Kovalev, E.M. Smirnova
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: metal alloying, laser radiation, convective heat and mass transfer, numerical simulation
Pages: 53-60

Abstract >>
Numerical simulation of metal surface alloying with impulse laser radiation has been performed. Impulse intensity influence on melt hydrodynamics and alloying substance distribution has been evaluated. For substance material, the authors used data on iron including dependence of surface tension on melt temperature and admixture concentration.

Calculation of radiation field in semi-transparent medium with consideration of incident collimated radiation

A.M. Timofeev
Ammosov North-Eastern Federal University
Keywords: radiation heat transfer, semi-transparent medium, collimated, anisotropic scattering, reflection
Pages: 61-67

Abstract >>
The mathematical model of radiation field in a semi-transparent medium formed under the action of incident collimated and diffusion radiation was developed and implemented numerically. To solve the problem, the approach on the basis of modified average flux method was developed. Method testing via comparison with results of other authors has proved its high reliability and accuracy. As an example, the effect of different factors on radiation field was analyzed: self-radiation of medium, scattering anisotropy, and bottom reflectance.

Heat transfer of an oscillating cylinder in a viscous incompressible fluid flow

T.V. Malakhova
Scientific Research Institute of Mechanics MSU
Keywords: viscous incompressible fluid, nonstationary heat transfer, forced convection, cylinder oscillations in fluid, flow separation, hydrodynamic wake
Pages: 69-76

Abstract >>
Unsteady flow and heat transfer of the heated cylinder with transverse and longitudinal oscillations in unbounded flow of viscous incompressible heat conducting fluid are considered. Influence of amplitude, frequency and direction of harmonic oscillations of the cylinder on the near-wake structure and heat transfer are investigated.

On dimensionless parameters for generalization pressure head and flow rate characteristics of centrifugal disk pumps

I.E. Naumov, YU.M. Prikhodko, V.P. Chekhov, V.P. Fomichev
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: disk pump, friction machine, dimensionless parameters
Pages: 77-82

Abstract >>
Experimental study was performed for operation of a centrifugal disk pump at atmospheric air pressure. The dimensionless parameters were developed for generalization of experimental data on flow rate and head of the pump. The method for calculation of a pumping curve and throttling characteristic was offered through use of semiemperical generalization formulas. The method ensures a good accuracy in calculations, which is proved by comparison of calculation and experimental data for the pump tested.

The modified absorption optic method for diagnostics of the wave liquid film on a rotating surface

I.K. Kabardin, V.V. Rakhmanov, V.G. Meledin, I.A. Eliseev, S.V. Dvoynishnikov
Kutateladze Institute of Thermophysics SB RAS
Keywords: absorption optic method, thickness field, wave film flow, rotating disk
Pages: 83-89

Abstract >>
The modification of absorption optic method for diagnostics of the wave liquid film on the surface of a rotating disk was proposed. Inaccuracy of the method was estimated analytically and experimentally. The field measurements of liquid film thickness on a rotating disk were carried out.

Modeling of wave regimes on the film of viscous liquid falling down a vertical plate

O.YU. Tsvelodub
Kutateladze Institute of Thermophysics SB RAS Novosibirsk State University
Keywords: falling film, model equation, evolution, family of solutions
Pages: 91-99

Abstract >>
Evolution of disturbances on the surface of liquid film falling free over a vertical plane is considered. In the case of low Reynolds numbers, the problem is reduced to investigation of a single equation describing evolution of film thickness disturbances. With the use of information about the structure of the family of steady-state traveling solutions to this equation, the typical scenarios of evolution for periodic disturbances were identified.

Investigation of the third heat transfer crisis on a vertical surface

B.P. Avksentyuk1, V.V. Ovchinnikov2
1 Vinnitsa Trade and Economics Institute of Kiev National University of Trade and Economics
2 Kutateladze Institute of Thermophysics SB RAS
Keywords: boiling, heat transfer crisis, evaporation front, subcooling
Pages: 101-107

Abstract >>
The process of development of the third heat transfer crisis for vertical orientation of the heating surface was studied experimentally. Experiments were carried out with acetone under the conditions of saturation for the pressures in the working volume from 20 to 28 kPa. In all experiments, the third heat transfer crisis was preceded by propagation of evaporation front along the heating surface. The threshold values of heat flux densities, above which a stable vapor film is formed on the whole heating surface, are lower for vertical orientation of this heating surface than for the horizontal one. Data on the threshold heat flux densities and overheating before boiling-up were obtained. Above these values, formation of evaporation fronts was observed. The range of operation parameters corresponding to formation of the sites of unstable film boiling on the heating surface after boiling-up was determined.

Heat transfer and crisis phenomena at boiling in Freon mixture films falling down the structured tube

A.N. Pavlenko1, N.I. Pecherkin2, O.A. Volodin2
1 Kutateladze Institute of Thermophysics SB RAS Novosibirsk State University
2 Kutateladze Institute of Thermophysics SB RAS
Keywords: heat transfer, film flow, nucleate boiling, crisis phenomena, dry spots, structured surfaces, Freon, binary mixtures
Pages: 109-119

Abstract >>
Investigation results on hydrodynamics, heat transfer, and crisis phenomena in laminar-wave liquid films falling down the surfaces of different geometry are presented in this study. Freon mixture R21/R114 with initial concentration of low-boiling component of 4−16.6 % was used as the working liquid. The film Reynolds number at the inlet to the experimental section varied from 60 to 700. The heat flux density was changed within 0−5 W/cm2. The images of wave surface of the falling liquid film and formation of dry spots were visualized and recorded by the high-speed video camera. Results of investigation of the wave structure of the film surface, measurements of heat transfer coefficients under the conditions of boiling, and critical heat fluxes in the film flow over the smooth and structured surfaces are presented.

Heat transfer at granulation of lead-containing aluminum alloys in aqueous medium

A.P. Skuratov, A.A. Pianykh
Siberian Federal University,
Keywords: aluminum alloys, alloying, lead, granulation, heat transfer, mathematical model
Pages: 121-127

Abstract >>
The work is devoted to investigation of thermophysical processes occurring at granulation of lead-containing aluminum alloys. The researchers proposed the mathematical model of heat transfer that served a basis for calculation of cooling of the alloy drops with different dimensions. With the use of laboratory experiment, the boundary conditions of simulation have been specified, and the quality of the obtained granules evaluated.

Removal of particle matter from dust-vapor-gas mixture in condenser with inclined tubes

L.V. Romanova1, I.I. Gogonin2
1 Saint Petersburg State Technological University of Plant Polymers
2 Kutateladze Institute of Thermophysics SB RAS
Keywords: wet steam, alkaline droplets, dust particles, dust-vapor cleaning condenser
Pages: 129-135

Abstract >>
The article presents results of the research of particulate matter and droplets removal on inclined tubes of the flue gas cleaning condenser in the process of vapor condensation of vapor-and-gas emissions from kraft pulp production.

Definition of effective coefficients of thermal conductivity in spatially reinforced composites on the basis of energy criterion of equivalence

A.P. Yankovsky
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS
Keywords: composites, structural theory, thermal conductivity, overall anisotropy, energy equivalence, upper and lower estimations, comparison with experiment
Pages: 137-148

Abstract >>
The models of thermal conductivity in fibrous spatially reinforced medium were developed at overall anisotropy of components; the approach is based on equality between dissipation in equivalent material and  the considered composite. The calculated values of effective coefficients of thermal conductivity for two cases (unidirectional and cross-loaded) composites were compared with experimental data. Agreement between calculated and experimental data is satisfactory. It was demonstrated that developed models give the upper and lower estimates for effective coefficients of thermal conductivity in fibrous compositions.

Numerical modelling of unsteady heating and melting of the anode by electric arc. Part 2. Numerical characteristics of the anode weldpool

R.M. Urusov, F.R. Sultanova, T.E. Urusova
Institute of Physical-Technical Problems and Materials Science of the National Academy of Sciences of Kyrgyz Republic
Keywords: electric arc, numerical modeling, anode unsteady heating and melting
Pages: 149-162

Abstract >>
Numerical computations of the electric-arc heating and anode melting were carried out within the framework of the two-dimensional unsteady mathematical model. The influence of the viscous interaction "plasma−melt", surface tension forces, electromagnetic forces, and gravitational convection on the formation of the hydrodynamics of the anode melt was considered.

Axisymmetric convective torch in fluid with power dependence of density on temperature

V.A. Sharifulin
Perm National Research Polytechnic University
Keywords: point source of heat, boundary layer, power dependence of density on temperature, point solution
Pages: 163-165

Abstract >>
The exact solution of boundary layer equations for laminar convective torch from point source of heat in fluid with power dependence of density on temperature was found.

60th Anniversary of Sergey V. Stankus

Editorial board
Pages: 167-168

Abstract >>
On January 30, 2012 Sergey V. Stankus, the prominent scientist working in the area of thermophysics, Doctor of Physics and Mathematics  and  Deputy Director of the Institute of Thermophysics, became 60 years of age.