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Thermophysics and Aeromechanics

2021 year, number 3

Structure of the flow in the near-wall gas jet injected through circular holes in a transverse trench

M.A. Pakhomov, V.V. Terekhov, M.V. Filippov, I.A. Chokhar, K.A. Sharov, V.I. Terekhov
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: near-wall gas jet, local flow structure, experiment, injection through cylindrical holes, trench, PIV

Abstract >>
Results of an experimental study of the local structure of the mean and fluctuating flow in a near-wall gas jet injected through inclined cylindrical holes along a smooth surface and in the case of injection in a transverse trench are reported. The local structure of the near-wall jet is measured by means of the particle image velocimetry. Injection of the secondary near-wall air jet into the main turbulent flow leads to a significant deformation of the streamwise velocity profile of the gas in both test cases. In the case of injection through the holes in the trench, the streamwise velocity of the gas displays a noticeably smoother profile with no clearly expressed maximum behind the cross section of the transverse trench exit. The streamwise velocity of the gas in the near-wall region has a smaller value than that in the case of injection without the trench. The transverse component of the gas velocity in the case of injection without the trench is greater than the corresponding value in the case of injection through the holes in the transverse trench after the gas leaves the trench.

Experimental study of the influence of external disturbances on the position of the laminar-turbulent transition on swept wings at = 2

Yu.G. Ermolaev, A.D. Kosinov, V.L. Kocharin, A.N. Semenov, N.V. Semionov, S.A. Shipul, A.A. Yatskikh
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: supersonic boundary layer, swept wing, laminar-turbulent transition, transition Reynolds number, vortex disturbances

Abstract >>
The influence of external vortex disturbances on the position of the laminar-turbulent transition in boundary layers on swept wings at the Mach number M = 2 is experimentally studied. The experiments are performed with two wing models; the sweep angles of the leading edges are 45 and 72. The vortex disturbances are generated by a wire placed ahead of the nozzles in the subsonic part of the flow. It is found that such disturbances increase the amplitude and change the spectral composition of oscillations in the boundary layer; moreover, they can induce earlier turbulization of the flow.

Stability of a supersonic boundary layer with heat supply to a narrow band of the layer

S.A. Gaponov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: boundary layer, stability, heat supply, flame, self-similar flow, flow disturbance

Abstract >>
The paper presents a study of a supersonic boundary layer while heat supply to the layers narrow internal region. Calculations were performed for a flow with Mach number M = 2 and the dimensionless temperature (normalized to the temperature at a layer boundary edge Tw = 3.9 (630 K). It was demonstrated that heat supply causes a two-fold increase in the 2D disturbance increments, while the frequency range expands by factor of three with a heat-insulated plate (zero heat input) taken as a reference. For a heated plate (with Tw = 3.9), the heat input into this layer delays the disturbance growth; that is, this facilitates the boundary layer stabilization and the disturbance increments reduce by almost four times. Along with 2D waves, the oblique waves were investigated in this paper. It was found that for low-frequency disturbance, we observe an intense growth of 3D (oblique) waves. Meanwhile, 2D disturbances enhance for a high-frequency range. These facts comply with the numerous data on boundary layer stability. However, these factors for boundary layer stability become less significant in the case of heat input to the supersonic boundary layer (compared with the zero heat input). The study also observes the longitudinal structures with a downstream decay. The heat supply makes these structures decrement lower in the supersonic boundary layer (meaning a slower decay). The results for the study of boundary layer disturbance are compared to similar data for the flow with M << 1.

Numerical simulation of turbulent flow around a 3D hydrofoil under the effect of corner separation

A.V. Sentyabov1,2, A.A. Gavrilov1,2, A.A. Dekterev1,2
1Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
2Siberian Federal University, Krasnoyarsk, Russia
Keywords: hydrofoil, numerical modeling, turbulence, RSM

Abstract >>
The paper presents the results of numerical simulation of three-dimensional turbulent flow around a hydraulic turbine guide vane at the angle of attack of 9º with the aspect ratio of the foil equal to 0.8. The influence of turbulence modeling variants on 3D flow effects is analyzed. The 3D boundary layer separation at the vane-sidewall junctions and the flow separation near the trailing edge influence the flow pattern. The study considered various approaches for modeling of a turbulent flow, such as the k-ω SST turbulent viscosity model and several variants of the differential and algebraic Reynolds stress models. At the given angle of attack, the k-ω SST model shows a significant separation zone in the corners between the wall and the vane, while no separation of the flow in the central plane is observed. Both differential and algebraic Reynolds stress models reproduce the secondary vortex flow at the corners and suppress the flow separation near the central cross section.

On the flow of a viscous liquid in a gravity field

V.L. Sennitskii1,2
1Lavrentyev Institute of Hydrodynamics SB RAS, Novosibirsk, Russia
2Novosibirsk State University, Novosibirsk, Russia
Keywords: viscous liquid, gravity field, oscillatory influence, steady motion

Abstract >>
A problem is formulated and solved on the motion of a viscous liquid in a gravity field. The liquid is in contact with curvilinear walls and is exposed by oscillatory influences which have no predominant direction in space. The problem formulation includes the equation of Navier-Stokes, the equation of continuity, and the conditions at the solid boundaries of the liquid. In particular, the new hydro-mechanical effect is revealed which consists in that the liquid behaves paradoxically that is performs a steady down up motion (at a background of oscillations).

Numerical study of flow control methods and splitting effects in a round submerged jet

A.K. Shevchenko, S.N. Yakovenko
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: round jet, axial perturbations, helical perturbations, mechanical vibrations, Strouhal number, jet splitting, numerical experiments

Abstract >>
The paper presents the results of numerical simulation of a submerged jet flowing from a circular hole in a wall with introduction of various types of perturbations. Active methods of flow control, including imposition of axial and helical harmonic oscillations on the inlet profile of the jet velocity, vibration of the jet nozzle, as well as their combinations, are considered. It is found that the external forcing leads to the effects of jet splitting at Reynolds number Re ≥ 1000 in wide ranges of perturbation frequencies and amplitudes, as it is shown in the studies of other authors. The mechanisms of interaction of vortex structures during jet bifurcation are investigated, and the angle of flow expansion in the bifurcation plane, which demonstrates an increase with a growing Re, is estimated. Calculations at 500 ≤ Re <1000 show that in order to obtain and enhance the above effects, it is necessary to optimize the forcing parameters, in particular, the type, frequency, and amplitude of perturbation. It is concluded that mechanical vibrations of the nozzle appear to be a more efficient way to control the flow than helical excitation of the inlet velocity profile.

The effect of baffles location on characteristics of gas pollutant transfer in the vicinity of motorways

S.A. Lavruk, S.A. Valger
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: microscale aerodynamic models, air quality, gas pollutants transfer, road transport, numerical simulation, turbulence models

Abstract >>
This paper studies approaches to numerical modeling of the transfer of harmful gas emission from low sources in the vicinity of the highways. A model problem of ethane injection through a system of low sources located on a flat plate imitating a road is considered in accordance with experimental data of. The influence of the turbulent Schmidt number on the processes of turbulent mixing of gases in the vicinity of a system of bluff bodies is investigated. Within the framework of numerical modeling, various configurations of baffles location in the vicinity of highways are considered and the most effective configurations are estimated in terms of air quality in pedestrian zones. A qualitative and quantitative comparison with experimental data on the profiles of ethane concentration in characteristic locations is carried out.

Linear stability analysis of Marangoni mixed convection flow for nanofluids in a horizontal open channel

L. Bammou1, K. Souhar1, S. Alami1, M. Feddaoui1, Y. Le Guer2
1Ibn Zohr University, Agadir, Morocco
2University Pau & Pays Adour, Pau, France
Keywords: mixed convection, thermoconvectives instabilities, thermocapillary effect, nanofluids

Abstract >>
This paper presents the linear stability analysis of laminar mixed convection flow combined to thermocapillary effect in a horizontal infinite channel heated uniformly from below. Pure water and water-based nanofluid containing various volume fractions of Al2O3 and Ag nanoparticles are considered. The results are presented for volume fractions up to 3 %. A spectral collocation method based on Chebyshev polynomials is implemented and the obtained algebraic eigenvalue problem is solved. In this study, the thresholds of the onset of the convective instability in the form of longitudinal and transverse rolls are determined numerically. The comparison between the pure water and the nanofluid flows allows to investigate the nanoparticles effects on the critical parameters for the onset of convective rolls. The combination of buoyancy and thermocapillary effects on the flow instability is studied and showing the competition between these two effects to make the flow more unstable in pure water and nanofluids. Critical wave numbers that describe the size of convective cells, in nanofluid flow are also presented, analysed, and compared with those of the pure water flow without nanoparticles. Besides, the effects of the type and the volume fraction of nanoparticles on the stability of the system are investigated.

Two-phase lattice Boltzmann simulation of nanofluid conjugate heat transfer in a microchannel

A.H. Saberi, M. Kalteh
University of Guilan, Rasht, Iran
Keywords: nanofluid, two-phase, lattice Boltzmann method, LBM, conjugate heat transfer, Nusselt number

Abstract >>
In this paper, numerical simulation of conjugate heat transfer of water-copper nanofluid is performed in a microchannel using two-phase lattice Boltzmann method (LBM), in which viscous dissipation is considered. In this study, the intermolecular forces such as drag, Brownian force, buoyancy, Van der Waals and Born forces are studied and analyzed. The magnitude of these forces is estimated and their degree of importance in the simulation is determined. Further, the effect of increasing the volume fraction and nanoparticles diameter on heat transfer and fluid flow is investigated. Finally, the effect of thermal conductivity of the microchannels wall on Nusselt numbers is investigated.

Vapor bubble growth in a zeotropic binary mixture

S.P. Aktershev, N.N. Mezentseva, I.V. Mezentsev
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: vapor bubble, zeotropic binary mixture, growth modulus, Jacob's criterion for the mixture

Abstract >>
In the framework of the thermal energy scheme, the growth of a vapor bubble in a uniformly superheated zeotropic mixture of two liquids is investigated. Formulas are derived for the bubble growth modulus and the Jacob criterion, which depends on both the physical properties of the mixture and its composition. The obtained solution for the constant composition of the mixture on the interfacial surface is an asymptotic case that limits the real rate of bubble growth. The results of calculations made for a mixture of R32/R152a freons of different compositions are presented.

Generation of composite particle material due to coagulation of several dispersed fractions in gas suspension flow

A.L. Tukmakov
Institute for Mechanics and Mechanical Engineering KSC RAS, Kazan, Russia
Keywords: two-fraction gas suspension, Navier-Stokes equations, Mac-Cormack explicit scheme, coagulation, composite materials

Abstract >>
The paper studies evolution of size distribution for a solid-and-droplet suspension gas flow with account for velocity slippage for the flow fractions. This process is described by the Eulerean model for polydisperse gas suspension: it consists of several fractions of metal solids and fractions of polymer droplets in air. The carrier medium (air) flow is described by a system of equations for motion of viscous compressible thermal-conductive gas with account for energy and momentum transfer to the suspended particle fractions. The dynamics of each of the dispersion fraction is described by gas dynamic equations with account for momentum and energy transfer from the suspension to the carrier flow. A set of equations for the gas suspension is formulated in general curvilinear coordinates and can be solved by the predictor-corrector explicit numerical method. The method comprises splitting of a space operator by directions and a nonlinear correction scheme for every time step. The coagulation of metal particle fractions and polymer fractions is described by Smolukhovskys model. This model considers the pair collisions of particles and calculates the physical parameters of each fractions (mass, radius, temperature, velocity and average density) for every time step of numerical simulation. The time and spatial parameters of metal and polymer particles coalescence in a gas flow are calculated with account for velocity slippage.

Deformation and crystallization processes of a nano-modified alloy droplet proceeding following its impact onto substrate: a modeling study

V.N. Popov, A.N. Cherepanov
Khristianovich Institute of Theoretical and Applied Mechanics SB RAS, Novosibirsk, Russia
Keywords: metal droplet, substrate, aluminum alloy, modification, refractory nanoparticles, heterogeneous nucleation, crystallization, numerical simulation

Abstract >>
Solidification of a binary aluminum alloy modified with refractory nanoparticles considered as active solid-phase nucleation centers is investigated. A mathematical model for the heterogeneous nucleation and crystallization of the melt is formulated taking into account the hydrodynamic processes in a droplet proceeding during the interaction of the droplet with the solid surface. This thermohydrodynamic problem is studied under conditions of sequential bulk crystallization of the metal. Thermal resistance on the contact surface of the melt with the substrate is taken into account. Regularities of the temperature change, and nucleation and growth, of the solid phase in a solidifying aluminum alloy are described. An estimate of the distribution of crystal-structure dispersity over the splat cross-section is reported.

Concerning the methods of thermocouple embedding in experimental studies of cooling the high-temperature bodies in subcooled and saturated liquids

A.R. Zabirov1, I.A. Molotova2, I.A. Belyaev1, V.A. Ryazantsev2, V.V. Yagov2
1Joint Institute for High Temperatures of RAS, Moscow, Russia
2Moscow Power Engineering Institute, Moscow, Russia
Keywords: boiling, experiment, thermocouple, micronucleate boiling, Leidenfrost effect

Abstract >>
The paper analyzes the methods of temperature measurements of cooling the high-temperature bodies in liquids. Experimental studies on cylindrical samples with different embedding of thermocouples have been carried out in three liquids. It is shown that even in the case of cooling in saturated liquids, external thermocouples, whose electrodes play the role of cooling fins, distort the measured temperatures significantly. Using external thermocouples, it is impossible to record correctly the rate of hot body cooling in liquid and the temperature of transition of cooling to an intensive regime. Using only a central thermocouple is permissible at low Bio numbers. However, even in this case, with intensive cooling, the difference between the temperatures of the center and the surface can reach several tens of degrees. With a decrease in the thermal conductivity of a sample and an increase in its linear dimensions, the temperature gradient increases (especially at intense cooling), and the correct physical interpretation of the process becomes impossible.

Planar thermometry using the method of spontaneous Raman scattering with structured laser illumination

D.K. Sharaborin
Kutateladze Institute of Thermophysics SB RAS, Novosibirsk, Russia
Keywords: structured laser radiation, spontaneous Raman scattering, swirling flames

Abstract >>
A method based on registering the distribution of spontaneous Raman scattering (SRS) intensity using structured laser radiation was employed to visualize and estimate the local distribution of temperature in pre-mixed laminar and turbulent methane-air flames. A comparison with the distributions of temperature measured by the Raman scattering method without modulated laser radiation is given. In the direction across the laser sheet in the measurement plane, the spatial resolution for the data with structured radiation proved to be lower than the spatial resolution for the data obtained without using structured radiation. However, even with the indicated disadvantages, the implemented approach makes it possible to estimate the average distribution of temperature in the reacting flow using the Raman signal recorded only with S-polarized laser radiation.

75th Anniversary of Vadim A. Lebiga

Abstract >>
On June 10, 2021, the well-known scientist in the field of viscous gas dynamics, Doctor of Technical Sciences, Professor Vadim A. Lebiga, celebrated his 75th anniversary.