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2022 year, number 3
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V.M. Boiko, V.V. Lotov, A.Yu. Nesterov, S.V. Poplavski
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: gas-liquid flow, supersonic underexpanded jet, aerodynamic breakup of droplets
Abstract >>
The goal of the study is to study the gas-dynamic structure of a supersonic underexpanded jet in the presence of a liquid spray as applied to the topic of gas-liquid nozzles. The wave structure is detected by methods of shadowgraphy and adaptive transparency visualization. Laser Doppler anemometry is used to measure the spray velocity and also to determine its concentration and droplet size. It is found that the flow in the two-phase core is qualitatively different from the gas jet flow. The transformation of the Mach disk in a wide range of gas flow regimes and liquid flow rates is studied. A crucial role of the gradient region of the jet in the vicinity of the Mach disk in the process of liquid atomization is demonstrated.
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S. Ilakkiya, B.T.N. Sridhar
Anna University Chennai, Chennai, India
Keywords: jet decay, jet structure, semi-circular grooves, supersonic core length, groove effectiveness
Abstract >>
Two diametrically opposite internal grooves were introduced in the diverging section of a supersonic nozzle. Experiments were conducted to find the effect of grooves at three different nozzle pressure ratios (NPRs), i.e., 3.6, 5.5, and 7.2 and comparisons were made with circular jet without grooves. Data reported here are for a design exit Mach number of 1.8 with an area ratio 1.44. Results are presented as pitot pressure decay along the extended geometric center-line of the nozzle and the radial distribution of pitot pressure at various axial ( x ʹ =1, 3, 5, and 8) locations. Empirical relations have been developed to identify the lengths of various regions involved in the pitot pressure decay (along X -direction). Groove effectiveness was used as a parameter to find the effect of grooves on the jet decay characteristics. The jet from grooved nozzle exhibited totally different results compared to that from plain circular nozzle. Results show that grooves played a more significant role at overexpansion condition of the nozzle than at under-expansion case. Schlieren flow visualization technique was used to capture the shock cell structure of the jets for the same NPRs and it was found that the structure of the jet emanating from the grooved nozzle was highly distorted. To understand decay characteristics, supersonic core length and the pitot pressure decay lengths for 50 % decay and 90 % decay were determined from the pitot pressure data along the extended centerline of the nozzle. A significant reduction in spatial pressure fluctuations and supersonic core length were observed at overexpansion condition of the nozzle when grooves were introduced.
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R.Kh. Bolotnova1, V.A. Korobchinskaya1,2
1Mavlyutov Institute of Mechanics UFRC RAS, Ufa, Russia
2Bashkir State University, Ufa, Russia
Keywords: thin nozzle, boiling water outflow, OpenFOAM package, mathematical and numerical modeling
Abstract >>
The fluid dynamics of a water fluid jet with supercritical state parameters outflowing from a high-pressure vessel through a thin nozzle is investigated. The numerical modeling of the jet was carried out using a system of equations for a gas-vapor-liquid mixture which includes the conservation laws for mass, momentum and energy formulated in with one-pressure, one-velocity, and two-temperature approximation. The simulation takes into account the contact heat and mass transfer processes of evaporation and condensation under equilibrium condition using a modified solver reactingTwoPhaseEulerFoam within the OpenFOAM free open package. The process of barrel shock formation in a supersonic boiling jet with developing the Mach disk is demonstrated. It was found that the outflow process is accompanied by formation of vortex zones near the jet symmetry axis and this induces periodic pulsations in pressure and mass velocity inside the jet. Finally, this generates the acoustic pulses series preceding the main jet flow. Justification of reliability for the applied numerical method implemented through the OpenFOAM package solver is offered through comparing the numerical and analytical solutions for the Sedov problem of a strong point explosion in a two-phase gas-droplet mixture (for the planar case). The comparative analysis of simulation and the experimental photography for the supersonic nitrogen jet ejected from a cylindrical nozzle of a high-pressure reservoir is presented. The numerical results obtained using the OpenFOAM package demonstrate a satisfactory agreement with analytical solution and experimental data.
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H.F. Ahmed, F.K. Malik, M.M. Khan
Capital University of Science and Technology, Islamabad, Pakistan
Keywords: drag reduction, wake stability, heat transfer, neural networks, blockage ratio
Abstract >>
Heat exchange devices involving confined heated cylinders in crossflow require wake stability to minimize hydraulic losses, which are typically accompanied by a considerable loss in heat transfer. To address this problem, passive wake control for laminar flow past a cylinder is introduced in the form of wavy channel walls around the cylinder. The resultant effects on heat transfer and drag are investigated in detail for a range of Reynolds numbers (Re = = 20 - 200), blockage ratios ( b = 0.5 - 0.9) and Prandtl numbers (Pr = 0.25 -100). For the given range of parameters, it is shown that the wavy channel reduces cylinder drag by a minimum of ~ 36 % and a maximum of ~ 95 %, at the expense of ~ 8 % and ~ 40 % loss in heat transfer, respectively, compared to the plane channel. Thermal-hydraulic performance of the wavy channel compared to the plane channel for Pr = 0.744, is improved by ~ 14 % for b = 0.5 and ~ 160 % for b = 0.9. Therefore, the performance enhancement brought about by the wavy channel provides an appropriate trade-off between drag reduction and heat transfer loss.
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B.F. Boyarshinov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: turbulence, acceleration, separation, combustion of a mixture, diffusion combustion, streamlines, isotherms, flame front
Abstract >>
The problems of interaction between gas dynamics and combustion are considered using the well-known database of experimental results on the boundary layer with ethanol combustion. Gas dynamics is represented by streamlines, combustion is represented by isotherms. The influence of an increased degree of air turbulence (up to 18%), acceleration in a narrowing channel, and the influence of the height of a flame stabilizing fin (3 and 6 mm) on the flow structure in individual cross-sections and in the boundary layer as a whole are studied. It is shown that immediately behind the barrier, where the signs of kinetic reaction of the gas mixture are manifested, the streamlines intersect, and during combustion in a narrowing channel with low air turbulence, the isotherms and streamlines become equidistant near the flame front, as in the case of diffusion response. Mass transfer on the liquid fuel surface remains conservative to changes in the gas-dynamic parameters of the air flow.
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A. Guelailia1, A. Khorsi2, S.A. Slimane1, A.M. Boudjemai1, A. Smahat1, P. Kumar3
1Centre of Satellite Development, Oran, Algeria
2University of Sciences and Technology Mohamed Boudiaf, Oran, Algeria
3Birla Institute of Technology, Mesra, India
Keywords: computational fluid dynamics, heat and mass transfer, turbulence, film cooling
Abstract >>
The present paper aims to investigate the effect of longitudinal curvature on film cooling performance through a single row of cylindrical holes. Four different longitudinal curvature cases are considered by changing the curvature heights. Detailed film effectiveness distributions are presented for several blowing ratios. The ANSYS CFX has been used for this computational simulation. The turbulence is approximated by a shear stress transport (SST) model. The numerical results are compared with experimental data.
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N.A. Pribaturin1, P.D. Lobanov2, V.S. Berdnikov2, A.S. Kurdyumov2, A.I. Svetonosov2, I.A. Evdokimenko2
1Nuclear Safety Institute RAS, Moscow, Russia
2Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: experiment, free convection, liquid metal, temperature
Abstract >>
Temperature distribution was measured during the development of natural convection in a vertical rectangular cavity 364 mm high, 185 mm wide and 40 mm deep, filled with a lead-bismuth melt and with the temperature difference maintained on its vertical sidewalls. The initial temperature difference was set by changing the electric power supplied to the heated wall, and, accordingly, by changing the heat removed from the opposite wall. The measurements were carried out in a quasi-stationary regime of free convection, when the flow parameters and temperature distributions over the cavity cross-section were constant for several hours. As a result of the performed measurements, the temperature profiles along the width and depth of the rectangular cavity were obtained.
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E.N. Vasil’ev
Institute of Computational Modeling SB RAS, Krasnoyarsk, Russia
Keywords: plate-finned heat exchanger, thermal resistance, thermoelectric cooling system, cooling capacity, coefficient of performance
Abstract >>
The processes of heat transfer in air and liquid plate-finned heat exchangers of a thermoelectric cooling system are considered. The flow modes in interfin channels are analyzed, and the local heat-transfer coefficients are determined. From the numerical solution of the two-dimensional thermal-conduction problem, the dependences of the thermal resistances of the heat exchangers on their geometric parameters are obtained. The influence of thermal resistances on the cooling capacity and on the coefficient of performance of the thermoelectric cooling system is determined. Optimization of heat exchangers in terms of fin thickness and interfin spacing has been performed.
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V.G. Borisova, V.A. Silantiev
Chaplygin Siberian Scientific Research Institute of Aviation, Novosibirsk, Russia
Keywords: optimization, inductive drag, tip surface, wing tip, Trefftz plane, circulation, aerodynamic design
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A numerical method of inductive drag reduction by means of improving the aerodynamic performance of the tip elements of lifting systems is presented. The method allows one to optimize the distribution of the intensity of free vortices at the wing tips in the Trefftz plane for a prescribed lift force and unchanged base wing geometry. Optimization calculations of various lift systems are performed, including the STR-40DT short-range airplane developed at the Chaplygin Siberian Scientific Research Institute of Aviation (SibNIA). Good agreement of the numerical and experimental results is noted.
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A.N. Pavlenko, V.E. Zhukov, N.N. Mezentseva
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk,Russia
Keywords: microarc oxidation, modifying coating, heat transfer, critical heat flux, freon, large volume, boiling, heat transfer
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Heat transfer and critical heat flux on flat rectangular (16´24 mm) heat-releasing surfaces (HS) made of aluminum alloy D16 and modified by microarc oxidation (MAO) were investigated. Two types of coatings made using different electrolytes were studied: KOH and phosphates. Coatings had good adhesion to the HS and high dielectric strength. The thickness of coatings was 20 and 7 µm, respectively. The studies were carried out using freon R21 under conditions of natural convection with horizontal orientation of the HS. For comparison, measurements were carried out on identical working sections without a modifying coating: the first section was polished; the second one was ground with a roughness of 20 μm. It was shown that the heat transfer intensity on the modified HS was not lower than on the HS polished with a roughness of 20 μm, and it was almost twice as high as that on the polished HS. The values of the critical heat flux on the studied surfaces were almost the same. The use of these types of coating provides electrical insulation of the heat-releasing element without compromising the efficiency of heat removal.
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V.A. Kuzmin, I.A. Zagrai, N.A. Shmakova
Vyatka State University, Kirov, Russia
Keywords: model liquid-propellant rocket engine, model solid-propellant rocket engine, thermal radiation, combustion products, emission characteristics, spectral radiation energy flux density, emissivity factor, temperature non-equilibrium
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The paper presents the calculated spectral densities of radiation energy fluxes and the emissivity factors of combustion products from model liquid and solid propellant rocket engines for the conditions of the combustion chamber, nozzle, initial and main sections of the plume. The influence of temperature non-equilibrium between gas and particle flows on the spectral and integral emission characteristics of combustion products is investigated. The calculated results of this work are compared with experimental and computed data of other authors. Particular attention is focused on the nature and level of emission at different locations of outflowing combustion products. The results of the work may be used to choose a section of the spectrum when determining the temperature of combustion products by pyrometric methods.
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A.A. Morozov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: gas expansion dynamics, pulsed laser ablation, direct Monte Carlo statistical simulation, Gaussian beam, flat-top beam
Abstract >>
In laser ablation, the nonuniform distribution of energy across the laser beam leads to a nonuniform heating and evaporation of the material from the irradiated surface. The influence of nonuniform temperature and that of the nonuniform flux of evaporated material from the surface on the laser-plume expansion dynamics during the nanosecond laser ablation in vacuum were studied. It was assumed that the surface temperature depended linearly on the laser radiation energy. Direct Monte Carlo simulation of pulsed gas expansion for a flat-top laser beam and for a Gaussian beam has been carried out under the assumption of no absorption of laser radiation in the plume. For the flat-top beam, the surface temperature proved to be areally uniform over the entire irradiation spot, whereas for the Gaussian beam, the temperature varied along the spot radius. It is shown that for both beams, the final distributions of particles in the plume are almost identical. However, in the case of the Gaussian beam the plume moves a little faster in comparison with the flat-top beam, which circumstance leads to an increased kinetic energy of particles passing through the time-of-flight detector by 2-4 %.
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M.A. Vasyutin, E.V. Danilova, N.D. Kuzmichev
Ogarev Mordovia State University, Saransk, Russia
Keywords: heat transfer, inhomogeneous heat equation, boundary value problem, beryllium copper, NbN film
Abstract >>
The process of heat transfer in NbN film while applying a pulse of current is considered using the 2D inhomogeneous heat equation. The boundary value problem is solved for a longitudinal cross-section in the film; the heat transfer problem is solved for a system “contacts-film-substrate-thermostat”. The temperature evolution for the film cross-section since the pulse start till the temperature relaxation is visualized. The maximum film heating is evaluated. It was shown that the contact material (beryllium cooper BeCu) ensures the effective heat drainage from a superconductive film existing in the resistance mode while passing a high density current through the film. The developed simulation method and the material for the contacts can be used for other types of metallic or semiconductor films.
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S.I. Lezhnin
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: direct pyrolysis of methane, analytical solution
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Analytical formulas are derived for describing the direct pyrolysis of methane in a bubble column loaded with a catalyst molt. This math can be implemented in research or commercial computer codes aimed to multiparametric optimization of the metal bath (with consideration of its cost and catalytic performance), setup dimensions and productivity. These analytical expressions can be used also for validation of numerical codes.
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Abstract >>
On May 27, 2022, Academician of the Russian Academy of Sciences Dmitry M. Markovich, a well-known scientist, scientific administrator, Director of the Institute of Thermophysics SB RAS, Chief Academic Secretary of the SB RAS, member of the Presidium of the Russian Academy of Sciences, celebrated his 60th anniversary.
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On May 2, 2022, Professor Valerian I. Yakovlev, a prominent specialist in the field of fluid, gas and plasma mechanics, Doctor of Physical and Mathematical Sciences, member of the editorial board of the journal "Thermophysics and Aeromechanics" turned 90 years old.
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