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Thermophysics and Aeromechanics

2020 year, number 4

Differences between the motion of a helical vortex and the movement of fluid particles along its axis

V.L. Okulov1, E.S. Gesheva2, P.A. Kuibin1, S.I. Shtork1, J. Sorensen1,3, D. Wood1,4, S.V. Alekseenko2
1Novosibirsk State University, Novosibirsk, Russia
2Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
3Technical University of Denmark, Lyngby, Denmark
4University of Calgary, Calgary, Canada
Keywords: vortex dynamics, helical vortex

Abstract >>
The motion of a helical vortex and the movement of the fluid particles along its axis are analyzed. The same form of the helical axis of the vortex and the trajectory of the particles sometimes leads to a false assumption of equality of these two different motions. The correct identification of both motions, however, is essential when considering the helical vortices in the wakes of rotors, or the displacement of the core of helicoidal tornado, etc. Only the same helical shape is the vortex axis and the streamline of the fluid particles can mistakenly merge these two different motions as the identical travel. We describe an experiment that clearly separates these two motions for the case of a stationary helical vortex, along the axis of which the fluid particles intensively move. The result shows that the absolute velocity of fluid particles does not coincide with the motion of the helical vortex as a whole.

Analytical solution for self-induced motion of a helical vortex with a Gaussian core

V.L. Okulov1,2,3, Y. Fukumoto4
1Novosibirsk State University, Novosibirsk, Russia
2Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
3Technical University of Denmark, Lyngby, Denmark
4Kyushu University, Fukuoka, Japan
Keywords: vortex dynamics, helical vortex, Gaussian vorticity distribution, self-induced rotation

Abstract >>
The paper presents an analytical solution for helical vortices with a Gaussian vorticity distribution in the core, which is confirmed by experimental and numerical simulations. This result is obtained by extending the Dyson method to the Biot-Savart law. Previously, analytical solutions were found and studied only for vortices with constant vorticity distribution in the core (a Rankine-type vortex core). One of the important issues raised during the discussion is the difference between self-induced movements of helical structures with both types of vortex core. The proposed solutions are important for the fundamental understanding and description of the behavior of helical eddy flows in various fields of industry and in nature. Examples include tip vortices behind the rotors of wind or hydro turbines, tornadoes, or axial vortices in aerodynamic devices such as vortex apparatuses and generators; cyclone separators, combustion chambers, etc.

Effect of the physicochemical models of the Direct Simulation Monte Carlo method on the aerodynamic characteristics of reentry vehicles

A.V. Kashkovsky1, P.V. Vashchenkov1, A.A. Shevyrin1, A.N. Krylov2, A.Yu. Skorovarov2, M.P. Shuvalov2
1Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
2S.P. Korolev Rocket and Space Corporation "Energia", Korolev, Moscow Region, Russia
Keywords: direct simulation Monte Carlo (DSMC) method, aerodynamics, reentry vehicle, chemical models

Abstract >>
Numerical studies of the aerodynamic characteristics of the Federation reentry vehicle are performed by the direct simulation Monte Carlo method for an altitude of 90 km. Quantitative effects of a number of physical and chemical models of this method on the aerodynamic performance of the vehicle are demonstrated.

Supersonic flow in the rectangular ductof an air inlet with the separation-induced interaction of the boundary layer with shock waves

I.I. Mazhul
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: supersonic flow, air intake, rectangular duct, longitudinal vortex structures

Abstract >>
Results of a numerical study of the flow structure in the rectangular duct of a model air inlet with the interaction of the shock wave generated by the inlet cowl with the turbulent boundary layer on the inner duct surfaces are reported. A configuration involving a convergent entrance section and a constant-cross-section throat was analyzed. The numerical simulation of the three-dimensional flow with free-stream Mach number M = 4 was performed on the basis of the Reynolds-averaged Navier-Stokes equations and the k-w SST model of turbulence. As a result of the calculations, the limit streamlines and the distributions of static pressure on the duct surfaces, as well as the distributions of total pressure and the fields of Mach number in duct cross sections were obtained. The structure of the flow is analyzed and the possibility of occurrence of longitudinal vortex structures in the corner region of the intake-duct throat is shown.

Film cooling behind two rows of trenches on a flat surface

A.A. Khalatov1,2,3, E Shi-Ju2, Dongyun Wang2, T.V. Donyk1,3
1Institute of Engineering Thermophysics NAS of Ukraine, Kiev, Ukraine
2Zhejiang Normal University, Jinhua, China
3National Technical University of Ukraine, Igor Sikorsky Kyiv Polytechnic Institute, Kiev, Ukraine
Keywords: trench, two rows of holes, efficiency of film cooling, computer simulation

Abstract >>
The paper presents the results of computer simulation of film cooling behind two rows of trenches on an adiabatic surface with coolant supply through inclined round holes located in the trench. The calculations were carried out in the range of injection parameter from 0.4 to 2.2 using the commercial computer package ANSYS CFX 14 and the SST turbulence model. It was found that for the injection parameter m > 0.6, asymmetry of the film cooling efficiency is observed behind the second trench, which increases with a growth in the injection parameter. This is explained by the unsteady nature of interaction of the cooling jets from the holes of the first and second rows. In the area between the first and second rows of trenches near the end strips the film cooling efficiency is 5-10% higher than near the middle ones, however behind the second trench it is 8-20% lower, which is caused by the staggered arrangement of the injection holes. For all injection parameters, the globally-averaged film cooling effectiveness near the end strips of the adiabatic surface is lower than that near the middle ones.

Development of unsteady convection in a rectangular cavity with sudden heating of a vertical wall

V.S. Berdnikov1,2, V.A. Grishkov1, N.A. Shumilov1
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Novosibirsk State Technical University, Novosibirsk, Russia
Keywords: thermal-gravitational convection, thermocapillary effect, thin vertical wall, free convective boundary layer, velocity fields, heat wave, physical modeling, digital video recording, thermal imager

Abstract >>
Unsteady thermal gravitational-capillary convection in a rectangular cavity with sudden heating of one of the vertical walls by electric current was experimentally investigated. The development in time of the spatial form of ethyl alcohol flows with the Prandtl number Pr = 16 at 20 was studied. The development of the hydrodynamic boundary layer on the heated wall and the flow along the free surface of a liquid layer was examined. The profiles of the vertical and horizontal velocity components were measured during the development of boundary layers and flow in a volume of liquid. Evolution of temperature fields on the free surface of a liquid layer was studied using a thermal imager.

Turbulent kinetic energy transfer and dissipation in thermoviscous fluid flow

Yu.M. Kulikov, E.E. Son
Joint Institute for High Temperatures RAS, Moscow, Russia
Keywords: thermoviscous fluid, turbulence, kinetic energy, mixing, Reynolds averaging, stationary turbulence, time scale, turbulent heat flux, inhomogeneous turbulence, filtration, averaging moments, advection, dissipation, diffusion, turbulent transport

Abstract >>
Turbulent flow of thermoviscous liquid is studied in a three-dimensional region with periodicity in two directions. Flow characteristics are described in the terms of equation for turbulent kinetic energy: this allows to differentiate contributions from different components related to generation, transport and dissipation of turbulent kinetic energy. Those terms can be calculated from averaging of moments of different order. The previous studies demonstrated that thermoviscous liquid flow occurs through several stages of evolution, including the unsteady turbulence. This allows discussing the problem of mathematical rigorous statement and applicability of different methods for averaging. Existence of spatial periodicity allow using a combined spatial-time averaging for different values on the interval of steady turbulence. Results are presented as a set of Z - t -diagrams. Besides, the paper presents analysis of flow development on the basis of direct visualization of velocity and temperature.

Development and application of the laser Doppler anemometer with direct spectral analysis for studying high-velocity multiphase flows

S.V. Poplavski, A.Yu. Nesterov, V.M. Boiko
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: laser Doppler anemometry, direct spectral analysis, high-resolution spectral devices, diagnostics of high-velocity multiphase flows

Abstract >>
The present study is aimed at the development of a laser Doppler anemometer (LDA) for investigating high-velocity multiphase flows. Based on the analysis of the Doppler anemometry methods, requirements to modern LDAs for solving the above-mentioned problems are formulated, and the ways of their implementation with allowance for the present status of laser engineering and spectroscopy are outlined. A prototype of the anemometer with direct spectral analysis with the most updated elemental base is presented. Its workability is demonstrated by an example of supersonic gas-liquid jets; it is also shown that the anemometer can be also applied to solve other problems.

Structure of a turbulent bubbly flow and heat transfer in a vertical tube

P.D. Lobanov1, M.A. Pakhomov1, V.I. Terekhov1, P.K. Das2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Indian Institute of Technology, Kharagpur, India
Keywords: bubbly polydisperse flow, tube, bubble spreading, heat transfer, wall friction, delta-approximation method, turbulence

Abstract >>
The results of numerical simulation of the flow structure and heat transfer in a vertical polydispersed bubbly flow are presented. The mathematical model is based on the Euler approach taking into account the effect of bubbles on the mean characteristics and turbulence of the carrier phase. The polydispersed distribution of bubbles size in a two-phase flow is modeled by the method of delta approximation considering the process of bubble break-up and coalescence. Carrier phase (fluid) turbulence is predicted using the Reynolds stress transport model. The simulation results showed good agreement with the experimental data presented in the literature. The measured and predicted thermal-hydraulic parameter distribution indicates that in a turbulent bubbly flow, the wall friction increase is greater than heat transfer enhancement.

Processes of fuel self-ignition and flame stabilization with transverse hydrogen fuel injection into a supersonic combustion chamber

M.A. Goldfeld
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: supersonic flow, ignition, combustion, flame stabilization, flow control

Abstract >>
The paper presents a study for conditions for hydrogen self-ignition and flame spreading in a supersonic combustion chamber at the Mach number for the inlet flow equal to 4. The experimental model is a rectangular channel with a flame stabilizer performed as a backward-facing step. The fuel was injected before the step at the top and bottom walls through 8 round orifices which were oriented at angles 45 or 90. Testing was performed for a wide range of flow parameters which were close to the flight conditions. The experiments performed allowed an efficient scheme of fuel injection for the processes of self-ignition and flame stabilization, which permits preventing choking the channel. It was found that the choice of the injection scheme and fuel injection pressure are critical for ignition conditions and allow controlling the combustion process.

Highly hydrophobic ceramic coatings produced by plasma spraying of powder materials

I.P. Gulyaev, V.I. Kuzmin, O.B. Kovalev
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: plasma spraying, suspension plasma spraying, diagnostics of two-phase flow, ZrO, bimodal surface structure, wetting angle, superhydrophobicity, highly hydrophobic coating

Abstract >>
Hydrophobic and highly hydrophobic zirconium oxide coatings are obtained by air-plasma spraying of powder and suspension materials. The proposed method and the developed equipment make it possible to obtain nanostructured surfaces with water-repellent properties. The high hydrophobicity of the coating is achieved by creating a hierarchical texture of its surface obtained by the combined method of plasma spraying of powder and liquid-phase materials. The developed surface of the coating based on zirconium oxide ZrO2 obtained by the method of sequential plasma spraying of micropowders (with 20-40 μm microparticle sizes) and liquid materials in the form of suspensions (with 50-100 nm nanoparticle sizes) makes it possible to increase the water-wetting angle up to 145 degrees.

Simulation of production of hollow silica particles in a plasma flow. Part 2. Hollow particle production dynamics

V.A. Arkhipov1, V.D. Goldin1, V.V. Shekhovtsov2, O.G. Volokitin2, A.S. Anshakov3, V.I. Kuzmin4
1Tomsk State University, Tomsk, Russia
2Tomsk State University of Architecture and Construction, Tomsk, Russia
3Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
4Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: low-temperature plasma, silica, precursor porous particles, particle heating and melting, hollow microspheres, Laplace pressure, morphology of microspheres

Abstract >>
The paper presents results of numerical simulation for the process of production of hollow microspheres during heating and melting of porous particles of silica (the precursor) by a flow of low-temperature plasma. This model takes into account the partial capturing of gas in the particle and offers the laws of evolution for the hollow microsphere diameter and the wall thickness for different precursors with the size D 0 = (50-150) microns and porosity P p = (0.2-0.6).

Impact of high-energy effects on the formation of internal structure in copper particles

A.E. Chesnokov1, A.V. Smirnov1, T.M. Vidyuk1,2
1Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
2Institute of Solid State Chemistry and Mechanochemistry SB RAS, Novosibirsk, Russia
Keywords: mechanical milling, mechanical activation, agglomerated particle, planetary mill, specific surface, plasma torch, spheroidization, dense spherical particle, hollow particle, composite material

Abstract >>
In the present paper, results of a study of the impact of high-energy effects on the surface morphology and on the formation of the internal structure in PMS-1 copper particles are reported. It is shown that the mechanical milling of the copper powder in a planetary mill leads to the formation of powder agglomerates with a layered structure consisting of numerous deformed ultrafine particles. It is found that the volume of the agglomerated particles involves defects in the form of microcracks and closed micropores with some content of the initial gas. Subsequent treatment of the powder in an argon-helium plasma jet leads to the formation of dense particles, as well as particles with distributed gas volumes or a single cavity. It was found that, as the molten metal interacted with localized gas volumes during the plasma treatment, local oxidation of the material occurred. A dispersion-strengthened structure with copper oxide compounds of a predominantly round shape, ranging in size from tens of nanometers to 7 μm and uniformly distributed over the particle volume, was formed.

Computational study of non-stationary thermal state of an ice layer taking into account radiation scattering

S.D. Sleptsov1, N.A. Savvinova2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Ammosov North-Eastern Federal University, Yakutsk, Russia
Keywords: ice, one-phase Stefan problem, radiation scattering, temperature field, melting rate

Abstract >>
Formation of a temperature field and melting rate of ice vertically located on an opaque substrate and scattering radiation at radiant heating were studied numerically. To solve the part of the problem concerning radiative heat transfer, we used a modified method of mean fluxes, which takes into account volumetric absorption and scattering of radiation in the medium, as well as the selective nature of the radiation source. The influence of spectral volumetric properties of ice on melting and temperature rise of the non-irradiated side is shown. Comparison of calculation results with experimental data shows satisfactory agreement.

Thermophysical properties of the liquid eutectic K-Pb alloy

A.Sh. Agazhanov1, A.R. Khairulin1,2, R.N. Abdullaev1,2, S.V. Stankus1
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: K-Pb eutectic alloy, thermal conductivity, temperature diffusivity, enthalpy, heat capacity, melt, laser flash method, drop method

Abstract >>
Using the laser flash method and the drop method, the thermal conductivity and the enthalpy increment of the eutectic K-Pb alloy (with a Pb content of 90.7 at.%) were measured in the temperature range from the liquidus point up to 1077-1175 K. The specific heat capacity and thermal diffusivity of the alloy were calculated. Approximation equations for the studied properties were obtained, and a table of reference data was developed. It was shown that the thermal conductivity of the liquid eutectic is less than that of pure lead and increases with temperature.

Liquid fuel spraying by a high-speed steam jet

I.S. Anufriev1, E.Yu. Shadrin1, E.P. Kopyev1, O.V. Sharypov1, V.V. Leschevich2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Luikov Institute of Heat and Mass Transfer NASB, Minsk, Belarus
Keywords: liquid fuel, steam, spraying, shadow photography method, size distribution

Abstract >>
The direct shadow photography method was applied for study of size distribution of droplets produced in liquid fuel atomization by a high-speed jet of superheated steam. This approach for fuel spraying allows eliminating the clogging of fuel lines and atomizers used for combustion of substandard liquid hydrocarbons. The setup has a long-focus microscope lens with optical magnification 7:1; this allows measuring the particles with the size starting from 1 m. Experiments revealed that the prevailing size of droplets in the fuel spray is 1-2 m.

80th Anniversary of Robert I. Nigmatulin

Abstract >>
On June 17, 2020 Robert I. Nigmatulin, the prominent scientist specialized in mechanics and mathematics, academician of the Russian Academy of Science became 80 years of age.