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卷 53, 编号 1 (2018)

Article

Flows of Supersonic Underexpanded Jets on the Range of Moderate Reynolds Numbers

Aniskin V., Maslov A., Mironov S.

摘要

The results of an experimental investigation of the gasdynamic structure of supersonic underexpanded air jets flowing out of a sonic nozzle into a low-pressure medium are presented. This setting of the experimentmakes it possible to achieve high values of the nozzle-to-ambient pressure ratio at moderate outflow Reynolds numbers characteristic of underexpanded jets issuing from micronozzles. The data on the supersonic core length, the laminar-turbulent transition location, and the jet flow characteristics are obtained. The results are compared with those obtained in microjets flowing out of sonic nozzles. Emphasis is placed on the earlier discovered effect of inverse transition of a turbulent jet into the laminar flow regime with increase in the Reynolds number.

Fluid Dynamics. 2018;53(1):1-8
pages 1-8 views

Asymptotic Analysis of Viscous Fluctuations in Turbulent Boundary Layers

Gorbushin A., Zametaev V.

摘要

A two-dimensional boundary layer of an incompressible viscous fluid is investigated in the presence of velocity and pressure fluctuations. The characteristic Reynolds number is high and, as a consequence, the unsteady (turbulent) boundary layer is thin. An asymptotic approach is used to analyze the complete unsteady Navier–Stokes equations, which makes it possible to separate out the characteristic viscous and inviscid flow zones in the boundary layer and to solve the corresponding problems. The analytical expressions for the viscous fluctuations governed by the Hamel equation with a large value of the parameter are derived.

Fluid Dynamics. 2018;53(1):9-20
pages 9-20 views

Vertical Momentum Fluxes Induced by Weakly Nonlinear Internal Waves on the Shelf

Vorotnikov D., Slepyshev A.

摘要

Free inertia-gravity internal waves in a two-dimensional stratified flow of an ideal fluid with a vertical velocity shear are considered in the Boussinesq approximation. The boundary-value problem for the amplitude of the vertical velocity of internal waves has complex coefficients; therefore, the wave frequency has an imaginary correction and the eigenfunction is complex. It is shown that the wave is weakly damped, the vertical wave momentum fluxes being nonzero and can be greater than the turbulent fluxes. The Stokes drift velocity component transverse to the direction of wave propagation is nonzero and less than the longitudinal component by an order of magnitude. The dispersion curves of the first two modes are cut off in the low-frequency domain due to the influence of critical layers in which the wave frequency taken with the Doppler shift is equal to the inertial frequency.

Fluid Dynamics. 2018;53(1):21-33
pages 21-33 views

Instability of a Charged Droplet in an Inhomogeneous Electrostatic Field of a Rod of Finite Thickness

Grigor’ev A., Shiryaev A., Shiryaeva S.

摘要

The instability of a charged droplet of an ideal liquid in an inhomogeneous electrostatic field of a rod of finite thickness maintained at a constant electrostatic potential is investigated within the framework of analytic asymptotic calculations. It is shown that the mode amplitudes and the drop oscillation frequencies increase with the rod thickness. The critical conditions of instability of the droplet reduce by several times as compared with the critical conditions of implementation of its instability in the electrostatic field of an infinitely thin filament maintained at a constant electrostatic potential. An analytic dependence between the charge and field parameters, critical for implementation of the instability of a charged droplet in an inhomogeneous electrostatic field and dependent on the rod thickness, is found.

Fluid Dynamics. 2018;53(1):34-48
pages 34-48 views

Motion of an External Load over a Semi-Infinite Ice Sheet in the Subcritical Regime

Sturova I.

摘要

The three-dimensional problem of steady-state forced vibrations of fluid and semiinfinite ice sheet under the action of a local external load traveling along the rectilinear sheet edge at a constant velocity is considered. Two cases are analyzed. In the first case the fluid surface outside the ice sheet is free and in the second the fluid is confined by a rigid vertical wall and the ice sheet edge adjacent to the wall can be both clamped and free. The ice sheet is simulated by a thin elastic isotropic plate floating on the surface of fluid of finite depth. The load traveling velocity is assumed to be not higher than the minimum phase velocity of the flexural-gravity waves (subcritical regime). The solution to the linear problem is obtained by means of the integral Fourier transform and matching the expansions of the velocity potential in the vertical eigenfunctions. Examples of the numerical investigation of the ice sheet and fluid displacements are given.

Fluid Dynamics. 2018;53(1):49-58
pages 49-58 views

Mechanism of the Emergence of Rogue Waves As a Result of the Interaction between Internal Solitary Waves in a Stratified Basin

Shurgalina E.

摘要

The features of the interaction between internal solitary waves are investigated within the framework of the completely integrable Gardner equation with positive cubic nonlinearity. It is shown that the soliton polarity affects radically the result of the interaction between the solitons. The role of the pair interactions between solitons of different polarities proceeding when rogue waves emerge in the soliton fields in a stratified basin is demonstrated. The effect of such interactions on the higher-order moments of the wave field is studied.

Fluid Dynamics. 2018;53(1):59-64
pages 59-64 views

Sustainment of Oscillations in Localized Turbulent Structures in Pipes

Nikitin N., Pimanov V.

摘要

The solution of the Navier–Stokes equations which reproduces some qualitative features of localized turbulent structures developed in circular pipes at transitional Reynolds numbers is numerically investigated. In the phase space this solution corresponds to the limiting state of the solution which evolves along the separatrix dividing the regions of attraction of the solutions corresponding to the laminar and turbulent flow regimes. Relative simplicity of the spatial and temporal behavior of the limiting solution on the separatrix makes it possible to investigate it in detail. In particular, the nonlinear mechanism of the onset of streamwise vortices responsible for sustainment of near-wall streaks whose instability ensures the presence of fluctuations is revealed.

Fluid Dynamics. 2018;53(1):65-73
pages 65-73 views

Distinctive Features of the Distributions of the Body Force Produced by a Plasma Actuator

Kuryachii A., Manuilovich S., Rus’yanov D., Chernyshev S.

摘要

Basing upon the assumption on the solenoidality of the field of the time-average body force produced by a surface dielectric barrier discharge analytical expressions for the spatial distributions of the components of this force are proposed. The calculations of the dischargegenerated near-surface jet are in good agreement with the experiment. The distinctive features of spatial distributions of the body force components calculated from the data of the velocity field measurements are physically explained.

Fluid Dynamics. 2018;53(1):74-85
pages 74-85 views

Generation of Three-Dimensional Disturbances in a Boundary Layer on Strong Interaction with a Hypersonic Flow

Dudin G., Neiland V.

摘要

Laminar boundary layer flow over an infinite-span, finite-length flat plate is investigated in the regime of strong interaction with a hypersonic gas flow. Under the assumption that an additional condition dependent on the transverse coordinate can be imposed on the trailing edge of the plate the flow functions are expanded in power series in the vicinity of the leading edge. It is shown that these expansions include an indefinite function dependent on the transverse coordinate. The corresponding boundary value problems are formulated and solved and the eigenvalues are determined. It is established that in this case the two-dimensional boundary layer can rearrange itself into a three-dimensional boundary layer.

Fluid Dynamics. 2018;53(1):86-94
pages 86-94 views

Investigation of Submerged Jets with an Extended Initial Laminar Region

Zaiko Y., Reshmin A., Teplovodskii S., Chicherina A.

摘要

The method of producing laminar submerged jets using a device, whose length is comparable with the jet diameter, is described. A submerged air jet, 0.12 m in diameter, produced by means of this technique is experimentally investigated in the Reynolds number range from 2000 to 13 000. Hot-wire anemometer measurements of the flow parameters and laser visualization of the flow are performed. It is shown that the device developed makes it possible to produce submerged jets with the laminar regions as long as 5.5 jet diameters. The initial regions of such jets can be used to study the development of disturbances in submerged jets, as well as used in medicine and engineering in organizing various gasdynamic curtains which produce zones with given properties with respect to purity and composition inside another gas media.

Fluid Dynamics. 2018;53(1):95-104
pages 95-104 views

Experimental and Numerical Investigations of the Characteristics of Pulsed Thermal Actuators

Voevodin A., Petrov A., Petrov D., Sudakov G.

摘要

The purpose of the study is to numerically, experimentally, and analytically investigate the characteristics of plasma pulsed thermal actuators (PT actuators) and to assess their possibilities in controlling flow around airfoils, wings, and configurations at large subsonic freestream velocities. For the PT actuators of the types considered the mathematical models adequately describing their effect on flow past bodies are developed. The characteristics of a prototype PT actuator are experimentally investigated on a specially developed rig. A new type of the PT actuator equippedwith a channel (PTC actuator) is proposed; it is designed to operate at a high pulse repetition frequency and at large flow velocities. Numerical investigations show that the PTC actuators are free of the essential and fundamental shortcoming of the PT actuators which consists in the working zone superheating at high pulse repetition frequencies.

Fluid Dynamics. 2018;53(1):105-118
pages 105-118 views

Acoustic Waves of Various Geometry in Multi-Fraction Bubbly Liquids

Gafiyatov R., Gubaidullin D., Gubaidullina D.

摘要

The propagation of acoustic waves of various geometry in mixtures of a liquid and a disperse phase consisting of small bubbles which differ from one another by both the radii and the thermophysical properties is investigated. A systemof differential equations of motion of the mixture is written and the dispersion relation is derived. The dispersion curves are constructed and damping of the pressure pulses is compared for the plane, cylindrical, and spherical waves in the bubbly liquids considered. The theory is compared with the experimental data.

Fluid Dynamics. 2018;53(1):119-126
pages 119-126 views

Numerical Modeling of Two-Dimensional Flow of a Nonhomogeneous Fluid in a Confined Domain

Garanin S., Kravets E., Pronina O., Stadnik A.

摘要

The pattern of the two-dimensional vortex flow of a nonhomogeneous fluid in a confined domain is studied using two-dimensional numerical calculations. It is found that in the case of a nonhomogeneous initial density distribution the kinetic energy decay rates are proportional to the square root of viscosity at the active stage of flow restructuring. The correlation functions of the velocity and the density are derived for different moments of time in the inertial range. All these results indicate the choice of the two-dimensional turbulence development scenario in a nonhomogeneous fluid.

Fluid Dynamics. 2018;53(1):127-135
pages 127-135 views

Oscillatory Motion of a Viscous Fluid in Contact with a Flat Layer of a Porous Medium

Kormilitsin A., Taktarov N.

摘要

Analytical solutions are obtained for two problems of transverse internal waves in a viscous fluid contacting with a flat layer of a fixed porous medium. In the first problem, the waves are considered which are caused by the motion of an infinite flat plate located on the fluid surface and performing harmonic oscillations in its plane. In the second problem, the waves are caused by periodic shear stresses applied to the free surface of the fluid. To describe the fluid motion in the porous medium, the unsteady Brinkman equation is used, and the motion of the fluid outside the porous medium is described by the Navier–Stokes equation. Examples of numerical calculations of the fluid velocity and filtration velocity profiles are presented. The existence of fluid layers with counter-directed velocities is revealed.

Fluid Dynamics. 2018;53(1):136-142
pages 136-142 views

Unsteady Rarefied Gas Flow with Shock Wave in a Channel

Titarev V., Shakhov E.

摘要

The two-dimensional time-dependent problem of rarefied gas flow in a plane channel, formed by parallel plates of finite length and closed at one end, is solved on the basis of the kinetic S-model. The flow develops as a result of rupture of a diaphragm which separates the gas at rest in the channel and the gas at rest in a reservoir of infinite volume. The effect of gas deceleration at the channel walls under the conditions of diffuse molecular reflection from the channel walls and end face is studied. Decay of a shock wave and disappearance of a homogeneous flow zone behind the shock wave is traced for three variants of conditions at the channel inlet: (1) gas enters the channel from a reservoir of infinite length and width (as the basic variant), the simultaneous motion in the reservoir and channel being studied; (2) the high-pressure reservoir represents a usual channel section; and (3) the motion of the gas in the reservoir is not considered at all, instead of this, the boundary conditions of the evaporation-condensation type under the conditions of gas at rest in the reservoir are imposed in the inlet cross-section.

Fluid Dynamics. 2018;53(1):143-151
pages 143-151 views

Status of the Navier–Stokes Equations in Gas Dynamics. A Review

Galkin V., Rusakov S.

摘要

The existing ideas on the status of the Navier–Stokes equations are changed in taking into account the following facts: generally speaking, the terms of these equations neglected in the boundary layer equations are of the order of certain Burnett terms in the conservation equations; the Navier–Stokes equations cannot be used to describe slow nonisothermal gas flows since in this case it is necessary to take the Burnett temperature stresses into account; and in the transport relations the Burnett terms determine certain effects (for example, the mechanocaloric effect).

Fluid Dynamics. 2018;53(1):152-168
pages 152-168 views

Visualization of Supersonic Low-Noise Flow Over Surface-Mounted Two-Dimensional Prisms

Liu X., Yi S., Gang D., Lu X.

摘要

An experimental study of supersonic flow over two-dimensional surface-mounted prisms is carried out in a Mach 3 low-noise wind tunnel. The noise level of this supersonic wind tunnel, defined as the root mean-square Pitot pressure fluctuation normalized by the mean Pitot pressure, can be reduced to about 0.37%. The nanotracer planar laser scattering (NPLS) technique is used to analyze the influence of the prism geometry and the oncoming flow conditions on the typical flow structures including separation and reattachment shocks. With increase in the prism height the induced shocks move upstream. At a constant streamwise length L of a prism the timeaveraged NPLS images show that the length of the downstream recirculation region increases from 0.8L to 1.2L, when the prism height H changes from 3 to 5 mm. As compared with the flow structures occurring downstream of the prisms, the upstream flow structures are more susceptible to the oncoming boundary layer and are considerably different in laminar and turbulent flows. The separation shock wave is clearly visible in turbulent flow even for the 1-mm prism, whereas in the case of laminar flow there is no a distinct shock wave upstream of this prism. At the same time, the location of the flow reattachment and the angle of the reattachment shock wave in the downstream flow remain almost the same in both two flow regimes.

Fluid Dynamics. 2018;53(1):169-175
pages 169-175 views