Structure of the flow in the near-wall gas jet injected through circular holes in a transverse trenchPakhomov, M. A.; Terekhov, V. V.; Filippov, M. V.; Chokhar, I. A.; Sharov, K. A.; Terekhov, V. I.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s086986432103001x
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.
Stability of a supersonic boundary layer with heat supply to a narrow band of the layerGaponov, S. A.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321030033
The paper presents a study of a supersonic boundary layer while heat supply to the layer’s 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 twofold 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 separationSentyabov, A. V.; Gavrilov, A. A.; Dekterev, A. A.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321030045
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 9° 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 fieldSennitskii, V. L.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321030057
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 jetShevchenko, A. K.; Yakovenko, S. N.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321030069
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 barrier location on characteristics of gas pollutant transfer in the vicinity of highwayLavruk, S. A.; Valger, S. A.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321030070
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 as applied to experimental data of [22]. 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 barrier 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 channelBammou, L.; Souhar, K.; Alami, S.; Feddaoui, M.; Le Guer, Y.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321030082
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 microchannelSaberi, A. H.; Kalteh, M.
2021 Thermophysics and Aeromechanics
doi: 10.1134/s0869864321030094
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 microchannel’s wall on Nusselt numbers is investigated.