Nº 3 (2025)
Articles
Numerical Analysis of Rarefied Gas Flow through a Periodic System of Channels
Resumo
Rarefied gas flows through a planar periodic system of rectangular channels (membrane) are analyzed in a wide range of Knudsen numbers. The problem is studied based on the numerical solution of the kinetic equation with the Shakhov -model collision integral and the Navier-Stokes equations of the compressible medium. The main attention is paid to the calculation of the mass flow rate as a function of the permeability, the relative channel length, and the rarefaction parameter.
Fluid Dynamics. 2025;(3):3–14
3–14
Self-Oscillations in an Axisymmetric Generator of Pulsed Jets and High-Frequency Regime Associated with Cavity Boundary Instability
Resumo
Liquid jet flows in the presence of a ventilated cavity with a negative cavitation number are investigated. The studies carried out in the Institute of Mechanics of Moscow State University show that under certain conditions cavitation-induced self-oscillations can occur in the hydraulic system with highly intense pressure fluctuations. The results of an investigation of the axisymmetric model of a pulsed jet generator with liquid jet outflow through a central orifice in a diaphragm and gas blow from the periphery beyond the diaphragm are presented. The two-phase medium outflow was realized through a convergent conical nozzle. The influence of the generator parameters and the distance to a wall (screen) on the efficiency of its operation is investigated. A narrow range of comparatively small blowing, in which high-frequency pressure oscillations are recorded, while the amplitude of impact pressure pulses on the screen is considerably higher than the amplitude of pulses in high-frequency generation regimes, is revealed. This flow regime can be due to the development of two-phase structures on the unstable jet boundary interactioning with the convergent nozzle walls. The evidence for the possible existence of this flow regime has been given by the solution of the plane problem of interaction between a finite jet and an inclined plate for different pressures on the jet surfaces. The problem was solved exactly using the methods of theory of functions of a complex variable for quasi-doubly-periodic theta functions.
Fluid Dynamics. 2025;(3):15–29
15–29
On Self-Similarity of Laminar Jets
Resumo
The problems of laminar jets that admit self-similar solutions are considered. A method for determining the self-similarity parameter is proposed based on the condition of existence of a solution to equations in self-similar variables under given boundary conditions with only a single self-similarity parameter. In problems of plane free and wall jets the self-similarity parameters are determined analytically. In the problem of a three-dimensional wall jet, the self-similarity parameter is determined using a neural network.
Fluid Dynamics. 2025;(3):30–36
30–36
Temperature Factor Effect on the Disturbance Propagation in the Flow past a Blunt Plate in the Interaction Regime
Resumo
Supersonic viscous gas flow past the upper surface of a blunt finite-length plate is considered in the interaction regime. The temperature factor effect on the pressure disturbances initiated by mounting a wedge at the plate end, the aerothermodynamic flow characteristics, and the disturbance propagation upstream are investigated. Numerical calculations are carried out within the framework of the solution of the stationary two-dimensional Navier–Stokes equations.
Fluid Dynamics. 2025;(3):37–46
37–46
Extended High-Current Arc Discharges in an External Magnetic Field in Gas Media
Resumo
Extended (up to several tens of centimeters) high-current (hundreds of amperes) electric arcs in various gases at the atmospheric pressure are studied experimentally and theoretically. Such discharges have been studied on the electric discharge stand of the P-2000 facility of the Institute of Mechanics of Moscow State University. The data on the influence of an external magnetic field on the stability of such discharges and the formation of branched current channels are clarified. One of the areas of the research is the study of the effect of the orientation of the magnetic field imposed on the arc on the processes of development of the discharge in various gas media, such as air, CO2, Ar, and N2. The data for argon and nitrogen are presented most fully. The experiments were carried out in a chamber with transparent walls. The calculation and the theoretical study are carried out on the basis of an electrical engineering model using the empirical data on the volt-ampere characteristics of arcs between graphite electrodes. It is found that the stability of high-current arcs is significantly affected by electrode jet-flame dynamics. At the same time, the traditional models of arcs in the external magnetic field without taking these factors into account show that the direction of the external axial field does not affect the stability of the arcs, affecting only the direction of their twisting during the development of helical instability.
Fluid Dynamics. 2025;(3):47–59
47–59
Hydrodynamic Instability of Spatially Periodic Flows of Homogeneous and Stratified Fluid with Regard for Friction. Formation of Steady-State Vortex Disturbances
Resumo
The stability of spatially periodic flows of homogeneous and stratified fluid is investigated with regard for bottom friction. The Galerkin method with three basis Fourier harmonics is used to solve the stability problem. A system of ordinary differential equations for the amplitudes of the Fourier harmonics is formulated. A solution to the linearized version of the system is obtained and an expression for the increment of disturbance growth is found. It is established that at the nonlinear stage of development the exponential growth of linear disturbances is replaced by the regime of establishing steady-state periodic disturbances in form of closed cells. These disturbances reduce the averaged horizontal velocity of the flow. Analytical expressions for the spatial period and amplitude of steady-state disturbances are obtained.
Fluid Dynamics. 2025;(3):60-72
60-72
Turbulent Boundary Layer on a Plate in Compressible Gas Flow
Resumo
For the compressible turbulent boundary layer, the results of the numerical study using the three-parameter RANS turbulence model are compared with the results of direct numerical simulation (DNS). It is shown that the calculation results using the RANS model are in satisfactory agreement with the DNS results at the Mach numbers from 6 to 14. This makes it possible to recommend the use of the RANS model in engineering calculations of the hypersonic boundary layer when there is no need for powerful computing systems.
Fluid Dynamics. 2025;(3):73–79
73–79
Vertical Momentum Transfer by Internal Waves with Regard for the Horizontal Component of Angular Velocity of the Earth’s Rotation
Resumo
Free internal waves in a uniformly stratified fluid are considered in the Boussinesq approximation with regard for the Earth’s rotation. It is shown that the dispersion relation, derived with taking into account the horizontal component of the angular velocity of the Earth’s rotation at constant wave frequency, is reduced to the canonical equation for second-order curves in the plane of horizontal wave numbers. If the wave frequency is higher than the inertial frequency and less than the Brunt-Vaisälä frequency, the frequency isolines are ellipses. If the wave frequency is higher than the buoyancy frequency, then the frequency isolines are hyperbolas; and if the wave frequency is equal to the Brunt-Vaisälä frequency, then the isolines are two straight lines parallel the direction to the east. The vertical wave momentum fluxes are obtained as functions of the direction of wave propagation. It is shown that the fluxes are maximum in absolute value when the wave propagates to the north or to the south. A comparison of the vertical momentum fluxes of internal and sub-inertial waves at the same length and the maximum wave amplitude is carried out. It is shown that the vertical momentum flux of sub-inertial waves is higher than that of internal waves and weakens with weakening of stratification.
Fluid Dynamics. 2025;(3):80-93
80-93
Simulation of One-Sided Convection in a Porous Medium Using a Nonlinear Equation of State
Resumo
One-sided density-driven convection in a porous medium is simulated numerically with reference to hydrodynamic processes occurring during injection of carbon dioxide into underground porous formations. When carbon dioxide dissolves in water or oil, the density of solution increases. This leads to the growth of instability. A hydrodynamic model that includes the continuity equation, the equation of motion (in the form of Darcy equation), and the convection-diffusion equation has been used. The equation of state that relates the density of the fluid phase to the concentration of carbon dioxide is nonlinear. The density of solution reaches a maximum at a certain concentration, which varies. A new computational code based on the finite-difference method has been developed to solve the problem. The effect of the concentration that gives the maximum density on the parameters of convective motion and mass transfer is investigated. In particular, it is found that if the maximum density occurs at a higher concentration, the amount of carbon dioxide that is transported downward by the convective flow increases. This means that, in this case, convective dissolution is more effective in trapping of carbon dioxide at depth.
Fluid Dynamics. 2025;(3):94–106
94–106
The Effect of the Delta Wing Vortex System on the Flow around Lifting Surfaces
Resumo
The vortex structures formed behind a delta wing in supersonic flow are considered. The dependence of these structures on the angle of attack and the oncoming flow Mach number is studied, together with their effect on the aerodynamic properties of a downstream straight wing. The regimes with M = 2 and 3 and α = 10°, 14°, and 20° are considered. The numerical data are obtained using the hybrid multiprocessor supercomputer K-60 system in the Common Use Center of the Keldysh Institute of Applied Mathematics of the Russian Academy of Sciences.
Fluid Dynamics. 2025;(3):107–119
107–119
Comparison of Newton's Problem Solutions for Axisymmetric and Non-Axisymmetric Bodies
Resumo
The effect of truncation of a body at the front face or edge on its aerodynamic drag is investigated. In the first case, the shape of the cross sections (circular, elliptical, diamond-shaped) does not change, and their area is determined by a power law dependence on the longitudinal coordinate. In the second case, the shape of the cross sections changes from a segment in the initial section to a circle in the closing section. The constructed bodies have the same length and base area. The drag was calculated using Newton's formula for the pressure coefficient.
Fluid Dynamics. 2025;(3):120–134
120–134
Numerical Study of Flow Structure in an Axisymmetric Channel with Injection of a Radial Jet along the Coanda Surface
Resumo
The results of numerical study of the flow in a channel with an annular radial jet injected along the Coanda surface are given. To describe the flow of the gas medium, the two-dimensional axisymmetric Reynolds-averaged Navier–Stokes (RANS) equations are used in combination with equations of the semi-empirical − −ω SST turbulence model. The effect of the total pressure and the width of radial jet on the velocity and static pressure distributions is studied and changes in the local structure developed at the sub- and supercritical pressure in the jet are described.
Fluid Dynamics. 2025;(3):135–146
135–146