


卷 54, 编号 3 (2019)
- 年: 2019
- 文章: 13
- URL: https://journals.rcsi.science/0015-4628/issue/view/9473
Article
Linear Stability of the Boundary Layer of Relaxing Gas on a Plate
摘要
The development of inviscid and viscous two-dimensional subsonic disturbances in the supersonic flat-plate boundary layer of a vibrationally excited gas is investigated on the basis of the linear stability theory. The system of two-temperature gas dynamics which includes the Landau-Teller relaxation equation is used as the initial model. Undisturbed flow is described by the self-similar boundary-layer solution for a perfect gas. It is shown that in the inviscid approximation excitation decreases the maximum growth rate of the most unstable second mode by 10–12% as compared with an ideal gas. The neutral stability curves are calculated for the first and second most unstable modes at the Mach numbers M = 2.2, 4.5, and 4.8. For both modes the critical Reynolds numbers at maximum excitation are greater by 12–13% than the corresponding values for the perfect gas.



Different Self-Oscillation Modes in Flows with a Ventilated Cavity and Their Possible Use in Forming Periodic Pulsed Jets
摘要
The problem of the generation of cavitation self-oscillations in a liquid flow in a pipe with two resistances is considered. The first resistance is a cavitator, behind which there is an artificial ventilated cavity, where the mean pressure is greater than the atmospheric pressure, while the liquid and gas outflow into the atmosphere takes place through the second resistance. Investigations show that the self-oscillation frequencies are chiefly determined by the cavity properties and the conditions of the outflow into the atmosphere. The generation of different self-oscillation modes is directly associated with the number of waves formed along the cavity length. It is shown that the pressure pipeline properties and the cavity volume have an effect on the cavitation self-oscillation mode (up to four frequency modes can be observable at the same geometry and hydraulic flow parameters). The question arises of whether the self-oscillations can be used for generating pulsed jets at the outlet. It seems that it is the first mode regime that is most suitable for producing the pulsed jets, since in this case the pressure fluctuations in the cavity are maximum. Using the exponential Voitsekhovskii nozzle the regimes, in which an intermittent jet flow of the liquid is realized at the outlet, are experimentally obtained.



Flow Characteristics in Coaxial Channels with Three Helical Fins of Annular Gap
摘要
The helical coordinate system is used for mathematical description of laminar viscous fluid flows in channels with three helical fins of annular gap. The mathematical model in which the equations of motion are written in projection on the directions of natural basis of the helical coordinate system is suggested. The distributions of flow characteristics in channels with long triple screw inserts of various geometry are analyzed on the basis of the numerical results obtained for the Reynolds numbers up to 806.



Nonlinear Internal Waves in the Shelf Zone of the Sea
摘要
The problem of internal wave propagation in the coastal zone is considered. The solutions describing the evolution of nonlinear waves above the shelf are constructed on the basis of the mathematical three-layer shallow water model. An analysis of the solutions obtained makes it possible to establish the basic laws of transformation of solitary waves and nonlinear wave packets of large amplitude in the shelf zone of the sea. New possibilities of application of analytical and numerical solutions to interpretation of natural experiments are discussed.



Interaction between Two Oppositely Swirled Submerged Jets
摘要
The problem of the interaction between two oppositely swirled jets of viscous incompressible fluid issuing from parallel tubes into the submerged space is considered. The scenario of the confluence of the two jets into a single jet is determined on the basis of a numerical solution. It is shown that far from the sources the flow is described by the self-similar axisymmetric Landau solution for a single swirled jet. The longitudinal vorticity field far from the source is also self-similar, with a complex decay rate. The asymptotic structure of the far field of the jet is discussed.



The Effect of Admixture of Non-Evaporating Droplets on the Flow Structure and Adiabatic Wall Temperature in a Compressible Two-Phase Boundary Layer
摘要
A mathematical model is constructed and numerical calculations of the problem of a highspeed longitudinal steady flow of a viscous heat conducting gas with an admixture of liquid droplets over a thermally insulated flat plate are performed. The droplet temperature is assumed to differ from that of the carrier gas. The range of flow parameters is considered, in which the droplet evaporation can be neglected but the temperature of droplets can vary significantly within the boundary layer. The mathematical model of two-phase boundary layer is modified taking into account the temperature nonuniformity inside the droplets. This required, along with solving the macroscopic equations of the two-fluid model, to find a solution of the heat conduction equation inside the droplets. On the basis of parametric calculations, the flow regimes with the formation of a liquid film due to droplet deposition on the wall are investigated. The similarity parameters are found and a range of governing parameters is determined in which, due to the heat exchange with the liquid phase in the boundary layer, a noticeable decrease in the adiabatic-wall temperature is manifested even at very small initial concentrations of the droplets.



Simulation and Calculation of Time-dependent Filtration of a Suspension in Dead-end and Open Channels with Regard to Dispersed Particles Diffusion and Deposit Formation
摘要
The model of filtration of a suspension in a channel is constructed within the framework of the diffusive approximation with regard to disperse component diffusion and deposit formation. The system of equations is reduced to the convective diffusion equation in integro-differential form. The equation obtained is integrated numerically. The constitutive parameters of the problem considered are established. Certain calculation results which illustrate the effect of the diffusive particle fluxes and the constitutive parameters on suspension dynamics in the channel are discussed. The behavior of mean filtrate flow as a function of time is analyzed for various values of the constitutive parameters.



Process of the Formation of Internal Waves Initiated by the Start of Motion of a Body in a Stratified Viscous Fluid
摘要
The mechanism of formation of three-dimensional internal gravity waves initiated by the start of motion of a disk of given diameter and finite thickness in the horizontal direction along the disk symmetry axis from right to left at a given uniform velocity in an incompressible viscous linearly density-stratified fluid is first considered in detail. The consideration is carried out on the basis of numerical solution of the system of Navier—Stokes equations in the Boussinesq approximation and visualization of the three-dimensional vortex structure of the flow calculated. The obtained fields of the velocity vectors and pressure perturbations possess horizontal and vertical symmetry planes passing through the disk symmetry axis. The process of formation of flow in the upper half-space caused by the shear and gravitational instabilities is described. In this process, two horizontal vortex filaments are initially formed between the back disk face and the place of pulsed start and then transformed into legs of the hairpin vortex loop whose head is located to right of the start point. Thereafter, vortex rings are periodically formed above the start point during half the buoyancy period of fluid. The left-hand halves of the rings are transformed into half-waves occupying space between the disk and the start point.



Heat Transfer and Thermophysics of Subsonic Dissociated-Air Jets in Flow past a Cylindrical Model in a High-Frequency Induction Plasmatron
摘要
Heat transfer in the subsonic high-enthalpy air flow in the VGU-4 induction plasmatron is experimentally and numerically investigated for three versions of the sectional discharge channel with the exit section diameters of 30, 40, and 50 mm. The model was a flat-nosed cylinder, 20 mm in diameter. Using a Gamma code the enthalpy he and the velocity at the jet axis are numerically reconstructed from the experimental data. The method for approximately determine the enthalpy he on the basis of the experimental data and the Fay—Riddell formula for the heat flux is proposed. The effective dimensionless model radius reff is introduced, which makes it possible to take account for the dependence of the flow at the outer edge of the boundary layer on the model and discharge channel geometries and the plasmatron operation regime. The value of reff is calculated for the VGU-4 operation regimes with a simple cylindrical discharge channel and a sectional channel. The values of the enthalpy he calculated using the “exact” and approximate methods are compared: the greatest difference in the he values amounts to 6%.



Propagation of a Shock Wave through a Viscous Heat-Conducting Gas in a Long Microchannel
摘要
The problem of unsteady gas flow in a channel between parallel plates initiated by the initial discontinuity of the pressure and density (Riemann problem) in the channel cross-section at the high pressure drops and moderately low Knudsen numbers is solved numerically on the basis of the full system of Navier—Stokes equations. The finite-difference scheme of the second order with respect to the spatial variables and time is used. The effect of the gas viscosity and thermal conductivity on the velocity of the shock wave and the nature of flow behind it is studied under the conditions of long channel and low gas density in the low-pressure section. The numerical solution obtained is compared with the available experimental and computational data.



Investigation of the Spectral Composition of the Gas Pressure and Thrust Pulsations in Nozzles Equipped with a Deflector
摘要
The results of a numerical and experimental investigation of the thrust and gas pressure pulsations on the thrust wall surface in annular and linear dual slotted nozzles are presented under the laminar flow conditions. The experiments are carried out in a pulsed aerodynamic setup using the products of combustion of acetylene-air mixture as the working body. The calculations are performed on the basis of Navier—Stokes equations for a multicomponent reacting gas medium using a chemically-nonequilibrium thermochemical model. The calculated and measured spectral compositions of the pulsating gas pressure at the center of the thrust wall of the annular nozzle are compared. The dependences of the pressure pulsation frequency and amplitude at the thrust wall center and the thrust on the gas pressures at the nozzle entry and exit, the dimensions of its critical section, and the deflector shape are established.



Heat Transfer Enhancement of Pulsating Flow in an Open Cavity Subjected to Uniform Magnetic Field
摘要
The present numerical work is devoted to the effect of an external magnetic field on a pulsating flow through an open cavity in a horizontal channel. The cavity is heated uniformly from the bottom wall. The finite volume method is used to solve the energy and Navier—Stokes equations. At the inlet of the channel flow pulsations are produced by adding a sinusoidal component to the velocity. The investigation is conducted for different Strouhal (0 ≤ St ≤1), Richardson (0.25 ≤ Ri ≤1), and Hartmann numbers (0 ≤ Ha ≤50) and for various aspect ratios of the cavity (L/H = 1, 1.5, and 2) at a pulsation amplitude A = 0.1. Various characteristics of the flow, such as isotherms, streamlines, and average and normalized Nusselt numbers are presented. The results indicate that the influence of the external magnetic field on the temperature distribution, flow field, heat transfer mode, and heat transfer enhancement rate vary with the Hartmann number. The effect of pulsations on the heat transfer enhancement is well correlated with the magnetic field intensity, Richardson number, and aspect ratio of the cavity.



Erratum
Erratum to: Distinctive Features of Pressure Fluctuation Fields on the Surface of Steps
摘要
Page 794, last line should read:
(acknowledgment: «This study was funded by the Ministry of Education and Science of the Russian Federation under subsidy agreement no. 14.625.21.0038 (project identifier RFMEFI62516X0038).


