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Thermophysics and Aeromechanics

2004 year, number 4

Review of methods for studying hypersonic gas flows past bodies with ablating coatings

N.I. Sidnyaev
Bauman State Technical University, Moscow, Russia
Pages: 489-508

Abstract >>
Means in most common use for reliable protection of aircraft surfaces against thermal loads are reviewed. Development of such means involves detailed consideration of mass-transfer processes on streamlined surfaces. Passive and active methods for thermal protection of surfaces are discussed, based on the use of ablating heat-shielding coatings. The review classifies studies, including those published recently, that confirm high efficiency and great potential of active heat-shielding systems for aircraft using forced blowing of coolants into boundary layer.

Determination of ultrasound absorption characteristics of thin porous coatings

I.S. Tsyryul’nikov and S.G. Mironov
Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Pages: 509-518

Abstract >>
Almost complete suppression of growth of the acoustic mode of disturbances in hypersonic boundary layers can be achieved by using special porous coatings absorbing sound. For testing conditions in hypersonic wind tunnels, rather smooth and thin coatings are required whose acoustic absorptivity is high in the high-frequency region and under low static pressure. In the present study, we examine acoustic properties of two types of coatings: with a regular pore structure and with chaotic porosity. By the acoustico-interferometric technique, we determined acoustic characteristics of both porous coatings in the region of audio frequencies and then calculated acoustic properties of the coatings in a broad range of frequencies. In performing the calculations, individual models for each type of materials were used. Direct measurements of acoustic absorptivity on aerodynamic models in the ultrasound range of frequencies under atmospheric pressure, and also the impedance of the coatings in the range of audio frequencies under reduced pressure well comply with model approximations.

Development of steady localized disturbances of laminar flow in attached and separated boundary layers

A.V. Boiko1, A.V. Dovgal1, and D.S. Lokhov2
1Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Pages: 519-524

Abstract >>
Steady localized disturbances (streaky structures) of a laminar flow with boundary-layer separation behind a step on the surface are experimentally studied. The results of the present work explain the previously found specific features of the structure in various conditions of their generation and show that the development of such disturbances in the flow-separation zone is outside the framework of the classical theory of hydrodynamic stability for shear flows.

Decay dynamics of fullerene C60 and endofullerene Li@C60 molecules excited by laser radiation

A.V. Bulgakov1, M. Heden2, A. Lassesson2, K. Mehlig2, F. Rohmund2, and E.E.B. Campbell2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2 Goeteborg University and Chalmers University of Technology, Goeteborg, Sweden
Pages: 525-535

Abstract >>
Decay dynamics of free fullerene C60 and endofullerene Li@C60 molecules excited by pulsed laser radiation has been investigated using time-of-flight mass spectrometry. Special attention has been paid to the phenomenon specific for clusters and called delayed ionization. A dramatic drop in the yield of delayed C60 is found to occur at large delays (longer than 10

Experimental investigation of premixed acetylene flame

V.V. Bakic, S.N. Oka, and N.D. Crnomarkovic
Institute of Nuclear Sciences "Vinca", Belgrade, Serbia and Montenegro
Pages: 537-548

Abstract >>
Entrainment of surrounding air into premixed acetylene flame leads to a change in velocity and temperature fields. In this paper the mixing process between the premixed acetylene flame and surrounding air, in different regions of the flame, for different air/acetylene ratios has been analyzed. Conditional and unconditional statistics of the LDA signals were performed using jet and/or air seed. Compared to commonly used unconditional statistics, conditional statistics of velocity fluctuations can give us more data about intensity of turbulent mixing in the flame. Mean velocity, turbulence intensity, and probability density function of instantaneous velocities have been measured in different cross sections of the flame, for premixed acetylene/air mixture with different air/acetylene ratios. The velocity field measurements were performed with the laser-Doppler anemometer, while for the temperature field measurements Pt-PtRhl0 % thermocouple was used. Relations between mean velocities and probability density functions have been established in cases of conditional and unconditional seeding. Mixing factor has been defined as a measure of mixing intensity. By comparative analysis of the obtained mean velocity and temperature profiles, the length and width of characteristic regions of the premixed acetylene flame and their characteristic properties were established for different fuel-air ratios.

Calculation of hydraulic drag for a short vortex chamber

V.V. Sorokin
Joint Institute of Power and Nuclear Research
Pages: 549-554

Abstract >>
The calculation method for hydraulic drag coefficient in a short vortex chamber is proposed for incompressible liquid flow. The method is based on the principle of maximal flow rate and integral method for computation of the turbulent boundary layer on the chamber cover wall. Results of calculations fit the available experimental data.

Study of pulsation characteristics of a swirl flow in cubic container

Yu.A. Anikin, I.V. Naumov, V. G. Miledin, V. L. Okulov, and O.Yu. Sadbakov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Pages: 555-559

Abstract >>
Results of experimental study about development of swirl flow instability in a cubic container are presented. The circumferential and axial components of velocity vector were measured with methods of laser Doppler anemometry for the range of Reynolds number 1000-2500. The scenarios of swirl flow development and pulsation growth moments are very different for the cases of cubic and cylindrical containers. The dependency of pulsation amplitude vs. Reynolds number shows that the starting point for linear growth of amplitude corresponds to Re = 1400. The spectral analysis demonstrated existence of different modes for flow disturbance at different Reynolds numbers: for the range 1400-2000 this pulsation is close to harmonic, and then extra modes are developing.

Laser Doppler diagnostics of flow structure downstream the rotor wheel in hydroturbine for optimal and boost loadings

O.Yu. Sadbakov1, V.L. Okulov1, I.V. Naumov1, V.G. Miledin1, Yu.A. Anikin1, N.P. Mostovsky2, and S.Ya. Il'in2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Laboratory of water turbines, Leningrad Metal Plant, OAO "Silovye Mashiny", St.-Petersburg, Russia
Pages: 561-566

Abstract >>
Experimental results on diagnostics of unsteady flow downstream of the rotor wheel in the draft tube (Francis turbine) are presented for transition from the optimal operation mode to the boost mode. The high-accuracy measurements of velocity profiles in swirl flow (turbid water flow with air bubbles) were carried out with a high-tech Doppler anemometor LAD05-LMZ equipped with semiconductor laser. This system is equipped with "Field Programmable Gate Array" facilities and uses the new method of adaptive detection of Doppler frequency. The comprehensive testing was performed for measurement technique and tools. The water flow rate obtained from the universal characteristics of the turbine model was compared with the flow rate computed from the measured profiles of axial velocity. The total error in the flow rate was less than 5 %.

Magnus wind turbine. 1. Results of model testing

N.M. Bychkov
Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Pages: 567-580

Abstract >>
The testing results are presented for a model of wind turbine in a wind tunnel; this turbine uses rotating cylinders instead of conventional blades. The main characteristics of the windwheel (power and high-speed) were measured at variation of different parameters: wind velocity, number of cylinders, their aspect ratio, rotation speed, loading for generator, and some additional changes in the cylinders shape. The performance of the windwheel was estimated for the parameters close to optimal.

Comparison of the model of the filtration of immiscible liquids with phase mobilities with the Muscat (Leverett model

O.B. Bocharov1 and I.G. Telegin2
1Lavrentiev Institute of Hydrodynamics SB RAS, Novosibirsk, Russia
2Institute of Water and Environmental Problems SB RAS, Gorno-Altaisk, Russia
Pages: 581-589

Abstract >>
Two filtration models with phase mobilities and phase permeabilities of Muscat

The problem of wet steam injection into porous medium

V.Sh. Shagapov1, I.R. Rakhmatullin2, and L.A. Nasyrova3
1The Sterlitamak
Pages: 591-602

Abstract >>
The problem of wet steam injection from a well into a porous medium is considered. The analytic solutions are obtained for the steam filtration region near the well within the framework of the homobaric approximation on the basis of which the effects of the pressure in the well, the temperature, and moisture content of the injected steam as well as the porous medium initial state on the peculiarities of the propagation of hydrodynamic and temperature fields in porous medium are studied. A critical condition is obtained under which the homobaric approximation may be accepted for the steam filtration region.

Bubbly downflow at a low void fraction

O.N. Kashinsky, V.V. Randin, P.D. Lobanov, and T.D. Chimitov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Pages: 603-608

Abstract >>
Results of experimental studies of local characteristics of bubbly downflow in a vertical pipe are presented. Measurements were carried out at reduced liquid velocities from 0.3 to 1 m/s and low volumetric void fractions (from 0.01 to 0.03). The local parameters of the flow were measured using the electrochemical method. Experimental results prove significant deformation of the two-phase flow structure in comparison with a one-phase flow even at low gas flow rate ratios. The effect of the gas phase on flow characteristics looses its intensity with a decrease in liquid velocity. It is shown that at a rise of the gas flow rate ratio in the two-phase flow, turbulent pulsation of liquid velocity in the near-wall region decreases.

The shape of a vapor cavity at explosive heterogeneous boiling

B.P. Avksentyuk1 and V.V. Ovchinnikov2
1Vinnitsa Institute of Trade and Economics of Kiev State University of Trade and Economics, Ukraine
2Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Pages: 609-616

Abstract >>
Investigation results on dimensions and shapes of vapor cavities forming at heterogeneous explosive boiling of organic liquids at saturation in the large volume are presented. The stainless steel tube of the outer diameter of 2.5 mm was used as test section. Heating of the test section was quasi-stationary. The process of explosive boiling was recorded with the speed of up to 25000 frames/second. According to investigations, the growth laws for transverse parts of vapor cavities formed due to evaporation front propagation are similar. In all experiments, the exponent in the law of transverse dimension growth was the same for all cross sections and it was equal to the exponent in the law of vapor bubble growth. The simulation dependency for the generatrix of vapor cavity at heterogeneous explosive boiling under conditions of saturation is suggested.

Determination of sedimentation rates for the birch and aspen pollen grains and their agglomerates

V.L. Istomin, K.P. Koutsenogii1, and V.V. Golovko2
1Lavrentiev Institute of Hydrodynamics, Novosibirsk, Russia
2Institute of Chemical Kinetics and Combustion, SB RAS, Novosibirsk, Russia
Pages: 617-626

Abstract >>
The modified method is described and edimentation rates for separate birch and aspen pollen grains and their agglomerates consisting of 9 and 6 particles are determined. Dependencies of agglomerate average sedimentation rate () on number of bounded particles (j), which set by relationships:  = 1,4 j0,405 for birch and  = 2,2j0,322 for aspen, are presented. Variability of the above values is demonstrated.

Thermal capacity of liquid freon R-236ea

A.V. Baginsky, S.V. Stankus, and A.S. Kosheleva
Kuteteladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Pages: 627-630

Abstract >>
Thermal capacity Cp of liquid 1,1,2,3,3,3-hexafluoropropane (R-236ea) is measured by the method of high-frequency heat waves within the temperature range from 264 to 354 K and at pressures up to 31.7 bar. Thermal capacity of liquid (Cps) is calculated at the liquid-vapor equilibrium line. Dependencies Cp(P,T) and Cps(T) are suggested.