Fluid Dynamics
Fluid Dynamics is the English version of the leading Russian journal Izvestia RAN, Mekhanika Zhidkosti i Gaza. It publishes original articles in the field of classical fluid and plasma dynamics, biomechanics of continuous media, flow in electro-magnetic fields, dynamics of multiphase and chemically reactive flow, including flow in porous media.
The journal publishes theoretical and experimental investigations. Numerical research should focus on new mechanical results with a short description of the numerical method itself.
The manuscripts are peer reviewed by two experts. In accordance with the "Statute of Scientific Journals of the Russian Academy of Sciences", the Editorial Board has the exclusive right to accept or reject manuscripts. According to the rules of our journal, authors will not be informed of the reasons for rejection. Papers are published free of charge to the authors and no fee is paid to them.
Media registration certificate: ПИ № ФС 77 – 82144 от 02.11.2021
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No 5 (2025)
Articles
STOCHASTIC MOLECULAR MODELING OF TRANSPORT PROCESSES IN GASES AND LIQUIDS
Abstract
The paper discusses stochastic modeling of flows and transport processes in both rarefied gases and liquids. In connection with the modeling of rarefied gas dynamics, the method of direct statistical modeling (DSSM) is considered. As previously established, this method effectively solves the basic kinetic equation (BKE) of a rarefied gas. It is shown how the BKE is derived directly from the Liouville equation. The BKE is derived for flows interacting with a solid surface, as well as for rarefied gases with rotational degrees of freedom. The connection of the kinetic equation obtained from the ODE with the Boltzmann equation is systematically studied. In particular, it is noted that when solving the ODE in a system of a finite number of particles, correlations characteristic of a dense gas rapidly increase. An algorithm for suppressing such correlations is proposed. In the second part of the article, a review of the method of stochastic molecular modeling of transport coefficients for both gases and liquids is provided.
Fluid Dynamics. 2025;(5):3-15
3-15
TO THE THEORY OF HYDRAULIC JUMPS IN FILM FLOWS ON ORDINARY AND SUPERHYDROPHOBIC SURFACES
Abstract
The paper analyzes the asymptotic formulations of the problems of thin-film flow structure on ordinary and superhydrophobic surfaces (SHS) with a given localized liquid mass supply into the film with the formation of "hydraulic jumps", i.e., sharp jumps in the film thickness. The analysis is restricted to the case of laminar flows without surface waves. The similarity parameters are obtained and the equations of the hydraulic approximation for viscous liquid film flows on a horizontal SHS in a gravity field are derived. A partial analogy is discussed with subsonic and supersonic flows of a compressible gas in the presence of external forces, according to which hydraulic jumps in a film are analogous to shock waves in gases. However, in the general case, changes in the total momentum flux (calculated based on the average velocity) and in the tangential velocity component in the film should be taken into account in the conditions on the hydraulic jump. Refined relations are derived for normal and oblique hydraulic jumps, taking into account the above mentioned changes in total pressure and tangential velocity, which depend on the liquid "slip length" on the SHS. Approximate models are proposed for determining the location of hydraulic jumps in steady-state one-dimensional flows with plane and axial symmetry. The fundamental role of the boundary condition for the film thickness (or velocity) in the "subcritical" region behind the hydraulic jump is emphasized in calculating the position of the jump. Examples of numerical calculations of one-dimensional flows with hydraulic jumps on SHS are given. The limits of the parameter region of existence of one-dimensional stationary solutions with flat or cylindrical hydraulic jumps are discussed. Outside these limits, the jump surface may take a polygonal shape, corresponding to the appearance of a system of oblique hydraulic jumps.
Fluid Dynamics. 2025;(5):16–34
16–34
UNSTEADY START OF THE LAVAL NOZZLE
Abstract
In the approximation of a two-dimensional flow of an ideal (inviscid and non-conducting) gas, the problem of a non-stationary launch of a Laval nozzle by an instantaneous rupture of the membrane at its exit is numerically solved for different ratios n > 1 of the pressures of the motionless gas inside and outside the nozzle. In the one-dimensional approximation, the stationary flow regime in a Laval nozzle changes from an unlocked subsonic flow (for 1 < n < n
*) to a locked sonic flow in the minimum nozzle cross-section (for n > n
*) with an easily determined value of n
*. The two-dimensionality of the flow complicates both stationary and non-stationary flow regimes in nozzles. In the two-dimensional stationary approximation, when n
* < n < n
**, the unlocked Taylor (Taylor G.) mode is realized, with supersonic zones near the walls of the minimum cross-sections of the nozzles, which is different from the locked Meyer (Meyer T.) mode. In the Meyer mode, when n > n
**, the supersonic flow covers the entire minimum cross-section, and in the vicinity of the "center" of the nozzle (the point where the sonic line meets the plane or the axis of symmetry), the flow is designed analytically. The numerically calculated non-stationary solutions did not confirm the known self-similar solutions of inverse problems about the launch of two-dimensional Laval nozzles.
Fluid Dynamics. 2025;(5):35-42
35-42
EQUATIONS OF MARANGONI BOUNDARY LAYER IN THE SECOND GRADE FLUID
Abstract
Second grade fluid is one of the basic mathematical models in dynamics of water polymers solutions. Equations of the Marangoni layer in such fluid are formulated. Solvability of linearized initial boundary problem for this equation is proved. The exact self- similar solution of mentioned equations is constructed. With the help of differential constraints method, solution of their solutions having a wide functional arbitrariness is found.
Fluid Dynamics. 2025;(5):43–49
43–49
STABILIZATION OF SUPERSONIC BOUNDARY LAYER IN MOLECULAR GAS BY LOCAL EXCITATION OF THE VIBRATIONAL MODE
Abstract
The paper investigates the influence of local energy input on the stability of a supersonic boundary layer on a flat plate with a Mach number M = 4.5 using a two-temperature model of a single-mode vibrationally excited gas. A source with a Gaussian power profile of low variance was placed near the upper boundary of the boundary layer. The real process of pumping the vibrational mode with laser radiation was modeled, in which part of the energy is transferred directly into heat. It is shown that in all cases, most of the layer is heated, its temperature increasing monotonically with the fraction of energy directly converted into heat. Calculations of the neutral stability curves showed that with increasing temperature, the critical Reynolds numbers Reδcr increase. In all regimes, the critical Reynolds numbers exceed the corresponding value for a perfect gas without energy input. This leads to the conclusion that the stabilizing effect of the source is achieved through heating of the upper and middle parts of the layer, leading to a decrease in the effective Reynolds number of the flow. A comparison of the critical Reynolds numbers Reδcr and of the transition Reynolds numbers ReδT was performed during pumping of the oscillatory mode with cooling of the wall up to the temperatures Tw
= T∞
, where T∞
is temperature of the carrier flow. The obtained data allow us to conclude that the compared methods are quite competitive.
Fluid Dynamics. 2025;(5):50–60
50–60
THE ONSET OF CONVECTION IN A SUSPENSION OF GRAVITACTIC MICROORGANISMS IN A HORIZONTAL LAYER
Abstract
The onset of bioconvection in a non-isothermal suspension of gravitactic microorganisms in a horizontal layer is investigated. It is shown that oscillatory instability is possible in the case of positive gravitaxis of microorganisms. The dependences of bioconvective thresholds, the critical wave numbers and the frequency of neutral oscillations on the Peclet number, as well as the Lewis number, and the concentration Rayleigh number are obtained and analyzed.
Fluid Dynamics. 2025;(5):61-69
61-69
WAVE GENERATION BY A PULSING DIPOLE IN A FLUID IN THE PRESENCE OF A SHEAR LAYER
Abstract
A linear problem of oscillations of a circular cylinder, modeled by a dipole, in a fluid with a shear layer, either near the surface or near the bottom, is solved. The presence of a shear layer results in the dispersion relation for the resulting wave motions having blocking points. For a near-surface shear layer, there are two, and for a bottom shear layer, there is only one. When the dipole oscillates with a frequency close to the blocking frequency, the amplitudes of some wave modes grow indefinitely, making the linear approximation unsuitable. The free surface elevations and interfaces between layers are investigated in a non-stationary problem where the dipole oscillations begin from rest, as well as the amplitudes of far-field waves during steady-state motion.
Fluid Dynamics. 2025;(5):70–82
70–82
NUMERICAL SIMULATION OF FLUID FLOW IN A CHANNEL WITH A LIMITED ARTIFICIAL GAS CAVITY AT THE OUTLET
Abstract
The applicability of the Simcenter STAR-CCM+ software package, the two-phase VoF model, and the Schnerr-Sauer cavitation model was assessed for the simulation of flows with a confined artificial cavity, accompanied by developed self-oscillations, transitioning to a discontinuous oscillation regime with large-amplitude pressure and flow rate pulsations. The obtained numerical simulation results for three-dimensional and two-dimensional flows were compared with experimental data. It was shown that the cavity behavior in the numerical simulation qualitatively matches the experimental data.
Fluid Dynamics. 2025;(5):83–92
83–92
FORMATION OF SMALL WATER CLUSTERS IN THE NEAR-NUCLEUS ATMOSPHERE OF A COMET
Abstract
The results of a theoretical study of the formation and decay of water clusters in cometary atmospheres are presented. A model for the formation of small water clusters is developed based on a quasi-chemical approach. The physical conditions for the formation and growth of clusters in near-nucleus coma are analyzed, depending on the distance of the cometary nucleus from the Sun, and possible mechanisms for cluster formation. Using the developed clustering model and the direct statistical Monte Carlo simulation method, calculations are performed for the outflow of water molecules sublimated from the surface of the cometary nucleus into vacuum. For the case of homogeneous condensation, using the nucleus of comet 46P/Wirtanen as an example, a small fraction of clusters (less than 0.1%) is determined for a cometary distance of 2.5 AU from the Sun for various distributions of gas production over the surface. The coordinated motion of small clusters and monomers is demonstrated.
Fluid Dynamics. 2025;(5):93–102
93–102
METHODS FOR DETERMINING UNSTEADY AERODYNAMIC CHARACTERISTICS OF AIRCRAFT MODELS IN AERODYNAMIC EXPERIMENT
Abstract
This paper provides a review of methods for measuring quasi-static and unsteady aerodynamic characteristics of aircraft models in wind tunnels. It presents the requirements of transport aircraft manufacturers for aerodynamic coefficient uncertainties. Existing methods for measuring unsteady aerodynamic force and aerodynamic moment using strain-gauge balances, non-stationary pitch and roll angles using a pendulum accelerometers, and unsteady pressure in wind tunnels are considered.
Fluid Dynamics. 2025;(5):103–119
103–119
SUPPRESSION OF DETONATION IN AN ACETYLENE-CONTAINING MIXTURE IN A PLANE CHANNEL WITH RECTANGULAR OBSTACLES
Abstract
The paper presents the results of a numerical study of the interaction of a formed cellular detonation wave propagating in a plane channel filled with an argon-diluted stoichiometric acetylene-oxygen mixture at rest, with single and multiple rectangular obstacles located in the channel. The study was conducted to determine the conditions that ensure the suppression of detonation. It has been established that to extinguish detonation combustion by a single obstacle, it is sufficient that its height exceeds a critical value depending on the channel width. For obstacles of subcritical height, methods of detonation destruction have been proposed by increasing the number of obstacles and choosing the distance between them.
Fluid Dynamics. 2025;(5):120-129
120-129
INFLUENCE OF EXTERNAL ELECTRIC CIRCUIT CHARACTERISTICS ON THE DEVELOPMENT OF A NANOSECOND PULSE DISCHARGE
Abstract
In this paper, a numerical study is carried out of the influence of the external electrical circuit elements on the processes inside the gas-discharge gap at the stage after the formation of a columnar spark channel closing the electrodes. A method for correcting the current in an electrical circuit based on solving a differential equation for the potential at the anode is proposed. The simulation is carried out for four variants of an external electrical circuit: short-circuiting the source on the electrodes (constant voltage at the interelectrode gap) and with ballast resistance in R, RC- and RLC- circuits. In the first two cases, a constant current source (electromotive force 25 kV) is considered, in the other two, a capacitor C charged at the initial moment (up to a voltage of 25 kV). The processes are modeled in molecular nitrogen at atmospheric pressure (the exception is the last case with a reduced pressure of 150 Torr). In all cases, current and voltage waveforms on all circuit elements were obtained and analyzed.
Fluid Dynamics. 2025;(5):130-150
130-150
EVOLUTION OF THE FLOW PATTERN AND ACOUSTIC RADIATION DURING THE MERGER OF A FREE-FALLING DROPLET WITH A LIQUID IN AN ELECTROSTATIC FIELD
Abstract
For the first time, synchronized high-speed recording of the flow pattern and acoustic pressure was performed using a hydrophone during the merging of a falling drop of distilled water with a quiescent liquid in an electrostatic field. This is in the impact flow regime, where the kinetic energy of the falling drop significantly exceeds its potential surface energy. In the electrostatic field, a reduction in the chronogram duration, a refinement of the flow pattern, an increase in the frequency, and a more complex structure of the resonant sound packet are observed. The observed changes reflect the influence of the electrostatic field on the droplet flow pattern, which is noticeably pronounced during the formation of the second and third cavities and during the detachment of gas cavities emitting a resonant acoustic signal.
Fluid Dynamics. 2025;(5):151–172
151–172