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2020 year, number 3
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V.S. Kaprilevskaya, A.M. Pavlenko, V.V. Kozlov, A.V. Kryukov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: swept wing, longitudinal structures, crossflow instability, laminar-turbulent transition, local roughness element, liquid crystal thermography
Abstract >>
The paper presents results of experimental study for a flow on the windward side of a swept wing with disturbance generators installed on the surface. These generators are 3D roughness elements with the height comparable to the boundary layer thickness. The method of liquid crystal thermography was used for studying the impact of roughness elements with different heights on the boundary layer. There exists a zone of maximal susceptibility of the flow to the disturbance generated past the roughness element on the wing surface.
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E.A. Chasovnikov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: re-entry vehicle model, free oscillations, pitching moment coefficient, aerodynamic characteristics, aerodynamic damping
Abstract >>
A method for treating experimental data obtained on a setup with free oscillations over the pitching angle of the model and for determining the unsteady aerodynamic characteristics of the pitching moment coefficient is described. It is found that the pitching moment coefficient of a re-entry vehicle model at Mach numbers M = 2 and 2.25 and fixed angles of attack a depends non-linearly on the rate of change of the angle a . This circumstance makes the concept of aerodynamic derivatives inappropriate for mathematical description of the pitching moment coefficient.
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V.P. Zamuraev, A.P. Kalinina
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: re-entry vehicle model, free oscillations, pitching moment coefficient, aerodynamic characteristics, aerodynamic damping
Abstract >>
A method for treating experimental data obtained on a setup with free oscillations over the pitching angle of the model and for determining the unsteady aerodynamic characteristics of the pitching moment coefficient is described. It is found that the pitching moment coefficient of a re-entry vehicle model at Mach numbers M = 2 and 2.25 and fixed angles of attack a depends non-linearly on the rate of change of the angle a . This circumstance makes the concept of aerodynamic derivatives inappropriate for mathematical description of the pitching moment coefficient.
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P. Promthaisong1, V. Chuwattanakul2, S. Eiamsaard1
1Mahanakorn University of Technology, Bangkok, Thailand
2King Mongkut’s Institute of Technology Ladkrabang, Bangkok, Thailand
Keywords: heat transfer, passive heat transfer, swirl, turbulent periodic flow, twisted square duct
Abstract >>
Heat transfer, local distributions of Nusselt number, flow structure, and friction characteristics of twisted square ducts are presented. Numerical analysis was carried out to investigate the influence of the twist ratio ( TR = p / D = 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0) on the thermal-hydraulic performance of twisted square ducts under constant wall heat flux condition for Reynolds numbers based on the hydraulic diameter of the twisted square duct ranging from 3000 to 20 000. The straight square duct was also analyzed for comparison. The numerical results showed that the twisted square ducts were more efficient in heat transfer than the straight square ducts because the swirl flow helped to increase fluid mixing and reduce thermal layer boundary thickness. The decrease of the twist ratio led to the increase in the Nusselt number and friction factor due to the higher frequency of swirl flow. As compared to the straight square duct, the twisted square ducts with TR = 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, and 6.0 improved heat transfer by 52, 49.82, 45.85, 42.22, 39.54, 35.41, and 31.77 %, respectively. Among the studied twisted ducts, the ones with twist ratio TR = 3.5 offered the maximum thermal enhancement factor of 1.42 at Re = 3000. In addition, the results also revealed that the twisted square ducts are thermo-hydraulically superior to the straight square ducts.
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V.I. Kornilov, A.N. Popkov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: airfoil, blockage, wind tunnel, pressure, aerodynamic characteristics
Abstract >>
The results of computational and experimental studies of the flow around a symmetric airfoil with a relative thickness of 12% in the free stream and in a low-velocity wind tunnel with a closed test section are presented. The experiments are performed for the Reynolds number Rec = 0.7·106-2·107 and angles of attack a = -12°¸ 12°. The problem is numerically solved in a 2D formulation by using the ANSYS Fluent software package. The mathematical model of the flow includes steady Reynolds equations closed by different turbulence models, including the k-w SST model, which is a superposition of the k - e and k-w models. A significant effect of blockage of the wind tunnel test section with limited dimensions by the airfoil on the flow character and aerodynamic characteristics of the airfoil even if the block-age coefficient is only 5.7% is demonstrated.
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M. Pirmohammadi1, A. Salehi-Shabestari2
1Islamic Azad University, Pardis, Iran
2Niroo Research Institute, Tehran, Iran
Keywords: magneto-convection flow, inclination angle, Rayleigh number, Hartmann number, Nusselt number
Abstract >>
In this study, laminar magneto-convection flow of a viscous fluid in an inclined enclosure is considered. The temperature gradient is applied on two opposing walls while the other two walls are maintained adiabatic. In order to solve the governing non-linear differential equations, an in-house developed code based on the finite volume method is utilized. The fluid of interest is molten sodium whose thermal and electrical properties such as heat capacity, thermal and electrical conductivity are temperature dependent. Representative results illustrating the effects of the enclosure inclination angle on the contour maps of the streamlines and temperature are reported and discussed. In addition, results for the midsection velocity profile and the average Nusselt number at the hot wall of the enclosure are presented and discussed for various inclination angles and Hartmann numbers. It is observed that for Hartmann number of 600, an increase in the inclination angle leads to the growth of the number of vortices in the enclosure.
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A.A. Gavrilov, A.V. Shebelev
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: suspension, turbulence, pipe flow, numerical simulation
Abstract >>
A model was developed for solids-liquid flow with any solids concentrations. The model includes the two-phase flow equations for the entire flow. It includes also the rheology law and the particle transfer equation with account for interphase slipping. The statistical model of turbulence accounts for the turbulence modulation by particles. The model was tested on a problem about a steady state flow with suspended heavy particles in a horizontal pipe. Comparison with experimental data and other accurate simulations demonstrated that this new model is useful for predicting the features of turbulent suspension flows. The secondary flows in a pipe show three-layered structure of the two-phase flow.
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M.A. Pakhomov, V.I. Terekhov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: film cooling, thermal efficiency, gas-droplet wall jet, injection through the holes, trench, numerical simulation
Abstract >>
The flow structure and thermal efficiency of a gas-droplet wall jet, injected through inclined holes into a transverse trench, is analyzed numerically. The predictions are carried out using three-dimensional RANS equations in the following ranges of two-phase flow parameters: initial droplet size d 1 = 0 -20 mm and their mass fraction M L1 = = 0 - 0.05. Gas turbulence is simulated using the model of Reynolds stress transport taking into account the two-phase character of the flow. The obtained simulation results are compared using the Eulerian and Lagrangian descriptions. The applicability of both approaches to describing the dynamics and heat transfer of a two-phase wall jet is shown.
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B.F. Boyarshinov, S.Yu. Fedorov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: cellular flame, non-contact measurements, PIV and CARS methods, momentum transfer
Abstract >>
To simulate a cellular flame, rich (equivalent ratio Ф = 1.4) and lean (Ф = 0.9) propane-butane/air mixtures were used in a burner, which forms a stationary flame with a single cell. Experimental data on the temperature fields were obtained using the coherent anti-Stokes Raman scattering (CARS) method; the velocity components were measured using PIV (Particle Image Velocimetry) equipment. The terms of friction stress and static pressure in the momentum transfer equations were calculated using the balance method. It is shown that the equality of dynamic and static pressures associated with the thermal expansion of the combustion products is satisfied on the cellular flame surface. Flameout occurs when the magnitude of the pressure head becomes greater than the magnitude of a static pressure change. The shear stress profiles contain extrema, whose coordinates are associated with streamline curvatures and are close to the position of the heat release region at combustion of lean and rich mixtures.
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P.A. Statsenko1,2, M.N. Khomyakov1,2
1Institute of Laser Physics SB RAS, Novosibirsk, Russia, Novosibirsk, Russia
2Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: laser cladding, particle flow, energy attenuation, modeling, diffraction approximation
Abstract >>
In laser cladding, the interaction of laser radiation with the powder flow and the substrate plays a key role. Surface heating depends on the distribution of radiation on the surface of the material, which is determined by the interaction of radiation with the flow of the powder microparticles. Usually, in models for calculating laser beam attenuation, the interaction of radiation with microparticles is limited to a simple geometric consideration based on the ratio of the cross-section area of the particles to the total area of the cross section under consideration, without taking into account the influence of diffraction. Radiation propagation is also considered in еру geometric approximation. The presented model allows taking into account the phenomenon of diffraction on powder microparticles. The results obtained using the model with radiation propagation in the geometric approximation are compared with the model with radiation propagation in the diffraction approximation proposed by the authors. It is shown that the numerical model of radiation attenuation and propagation in the diffraction approximation is applicable for complex analysis of the interaction between a laser beam, a particle stream, and a surface. The model allows estimating the beam attenuation due to interaction with the flow of microparticles and obtaining the intensity distribution on the surface of the substrate.
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S.P. Rusin
Joint Institute for High Temperatures RAS, Moscow, Russia
Keywords: true temperature, radiance temperature, gray approximation
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The graph-analytical method (gray model) for estimating the true temperature of an opaque material from both above and below at the unknown character of emissivity dependence on the wavelength is presented. It is shown that if the diagram of spectral distribution of inverse radiance temperatures in the selected spectral range can be approximately represented by a line, convex downwards, then the obtained value of the spectral ratio temperature limits the true temperature from above. If the diagram of indicated dependence in the spectral interval can be represented by a line, convex upwards, then the obtained value of the spectral ratio temperature limits the true temperature from below. The solution to this inverse problem should be combined with the solution to the direct problem. As a result, additional information on the spectral distribution of the material emissivity in the selected spectral range appears. In addition, this is verification of the assumptions made. The paper also provides an example of processing experimental data known from publications.
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V.V. Bakovets1, A.V. Sotnikov1, A.Sh. Agazhanov2, S.V. Stankus2
1Nikolayev Institute of Inorganic Chemistry SB RAS, Novosibirsk, Russia
2Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: real structure, thermophysical properties, sulfides of rare earth elements, solid solutions
Abstract >>
The work is devoted to the study of temperature dependences of thermal conductivity (T = 300-770 K) of polycrystallic samples of solid solutions based on gadolinium and dysprosium sulfides of the compositions: γ-Gd x Dy1- x S1.49 (x = 0.1, 0.2, 0.3, 0.4). It has been found that the morphological features of samples, namely, the specific surface area of crystallites, which causes a change in the number of deformation centers, determines the value of the thermal conductivity of γ-Gd x Dy1- x S1.49 solid solutions. The presence of an abnormal decrease in thermal conductivity for the composition of x = 0.2 has been established. When the temperature increases to 770 K, this anomaly decreases slightly. The minimum value of the thermal conductivity coefficient of 0.68 ± 0.03 W/(m×K) is reached for the com-position under consideration·at 770 K.
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V.N. Popov, A.N. Cherepanov, V.G. Shchukin
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: crystallization, binary alloy, nucleation, modification, nanosize high-refractory particles, numerical simulation
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A mathematical model of solidification of an iron-based binary alloy (Fe-C) modified with nanosize high-refractory particles is proposed. The processes of alloy heterogeneous nucleation on the surface of nanosize particles and those of alloy crystallization in a cylindrical mold are described. For liquidus temperature, a linear approximation of the concentration of dissolved carbon is adopted; the law of change of this temperature obeys the non-equilibrium lever rule. The volume of the solid phase formed around a nucleus during the crystallization determines the characteristic size of the grain structure in the solidified alloy. Numerical simulation of melt solidification in a cylindrical crucible was carried out, and the kinetics of heterogeneous nucleation and growth of the solid phase was analyzed. It was found that the conditions for nucleation and crystallization differ substantially within the casting. It is shown that, as the melt undergoes cooling, volume-sequential crystallization gets established.
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P.D. Lobanov1,2, E.V. Usov1, A.I. Svetonosov1,2, S.I. Lezhnin1,2
1Nuclear Safety Institute RAS, Moscow, Russia
2Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: nuclear power, fuel element, severe incident, melt, film, rivulets
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The paper presents the results of experimental study on melting simulator of the fuel coating pin cladding made of alloy Pb (44.5 %)-Bi (55.5 %) and the flow of the melt on the surface of the heated rod. Experiments were conducted for different parameters: heat release, initial temperature, linear size, and the cladding thickness. All experiments provided the video of the process of formation and relocation of the melt, and the cladding temperature and mass loss rate were measured. The paper presents analysis of melt formation and relocation on the fuel rod imitator surface.
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A.Sh. Agazhanov, R.N. Abdullaev, S.V. Stankus, D.A. Samoshkin
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: Rb-Bi alloy, thermal conductivity, thermal diffusivity, melt, intermetallic complexes, laser flash method
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Using the laser flash method the thermal conductivity of the Rb-Bi liquid alloy with a bismuth content of 27 at. % was measured in the temperature range from the liquidus point to 1173 K. Approximation equations for thermal conductivity and thermal diffusivity have been obtained, and a table of reference data has been developed. An analysis of the measurement results confirms the existing assumption of the presence of intermetallic complexes with a partially ionic nature of the interatomic interaction in Rb-Bi melts.
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Abstract >>
On May 30, 2020, the outstanding Russian scientist in the field of thermophysics, energy, and energy saving, Academician of the Russian Academy of Sciences, Scientific Director of the Institute of Thermophysics SB RAS Sergey V. Alekseenko turned 70 years of age.
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Abstract >>
On April 24, 2020, the famous scientist in the field of fluid mechanics, Doctor of Physical and Mathematical Sciences, Professor Viktor V. Kozlov became 75 years of age.
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