Table of contents

These proceedings are the output of VII Perm Hydrodynamical Forum (PHD-Forum 2020). The conference was held by Perm State University and Institute of Continuous Media Mechanics UB RAS in Perm, Russia on October 22-24, 2020.

The conference was dedicated to the memory of the leaders of the Perm Hydrodynamic Scientific School - the Leading Scientific School of the Russian Federation, Professors G.Z. Gershuni, E.M. Zhukhovitsky, and D.V. Lyubimov. It was devoted to the analysis of the advanced problems in Hydrodynamics and discussion of ways to solve them, the exchange of the scientific achievements and practical experience, the establishment of new and strengthening the existing scientific communications, the creation of the necessary conditions to stimulate and support young scientists, the dissemination and popularization of scientific knowledge and innovative technologies.

The work program of the Conference included the discussions on the current state and advanced problems of Mechanics and Physics of Continuous Media in the following directions:

1 - Large scale vortex structures in turbulent flows

2 - Heat and mass transfer in the atmosphere and ocean

3 - Generation of magnetic fields by the turbulent flow of electrically conductive fluid

4 - Dissipative structures on the interphase boundaries. Hydrodynamics of systems with interfaces

5 - Hydrodynamic stability and transition to chaos

6 - Unsteady flows in complex fluids and multiphase media

7 - Acoustic and wave processes in inhomogeneous media

8 - Applied aeroacoustics and aerospace engineering

9 - Eco-hydrodynamic modeling of water bodies and aquatic ecosystems

List of Short Programm of VII Perm Hydrodynamical Forum(PHD-Forum 2020), Scientific Committee are available in the pdf.

All papers published in this volume of Journal of Physics: Conference Series have been peer reviewed through processes administered by the Editors. Reviews were conducted by expert referees to the professional and scientific standards expected of a proceedings journal published by IOP Publishing.

• Type of peer review: Single-blind peer review by two committee members

• Conference submission management system: submissions were received and handled via e-mail

• Number of submissions received: 94

• Number of submissions sent for review: 62

• Number of submissions accepted:40

• Acceptance Rate (Number of Submissions Accepted / Number of Submissions Received X 100):45%

• Average number of reviews per paper: 3

• Total number of reviewers involved:17

• Any additional info on review process: all the papers were reviewed

○ by the scientific editor;

○ by two independent referees (normally one committee member and one external reviewer);

○ by the language editor.

• Contact person for queries:

Tatyana Lyubimova, scientific editor, Dr. of Sci., professor Department of Theoretical Physics, Perm State University, Perm, Russia, lubimova@psu.ru

Continuous-flow microfluidic devices are applied in the study of microorganisms, in genetic research, production of pharmaceutical substances, lab-on-a-chip technology, biomedicine etc. Some applications require continuous mixing of the solutions that flow through the devices. However, straight-line mechanical mixing methods cannot be used due to the small size of the channels. In this paper, we discuss from a theoretical and experimental point of view the prospects of using various mechanisms of natural or forced convection for efficient mixing of solutions entering a microfluidic chip. Different designs of micromixers operating on gravity-dependent instabilities of the Rayleigh-Taylor type, double diffusion convection, and surface-dependent Marangoni instability are considered. Micromixers, in which the fluid flow is controlled by an electro-osmotic mechanism and directional deformations of the channel walls, are considered as examples of forced convection. For each case, we will provide the assessment of the range of chip sizes in which this mixing mechanism works effectively. The examples of experimental implementation of different mixing principles are given.

The paper describes an algorithm for solving the Stefan problem by the finite element method for modeling heat and mass transfer processes in a fluid with a phase transition. Modeling of heat and mass transfer is based on the solution of the Navier-Stokes equations for an incompressible fluid in the Boussinesq approximation and the heat conduction equation for a solid phase. The solution was made according to the explicit-implicit scheme of the matrixless finite element method using a moving finite element mesh. The mobility of the grid nodes is due to the variable geometry of the solution region due to the motion of the melt-crystal interface. The new positions of the nodes of the moving mesh were calculated by the model of elastic media, providing the approximate equality of the volumes of the mesh cells. The grid nodes belonging to the moving boundary between the melt and the growing crystal moved in accordance with Stefan's conditions. The auxiliary systems of algebraic equations for the nodal values of the desired functions were solved by the matrixless conjugate gradient method with preconditioning by using the diagonal approximation of the stiffness matrix. An example of the application of the described finite element implementation of the Stefan problem for modeling of process for semiconductor single crystal growth by the Bridgman method taking into account the rotations of crystal, crucible and heater-vibrator is given.

The results of direct numerical simulation are intended to describe the saturation process of a nanofluid through artificial porous medium. The calculations were fulfilled using the hypothesis, which presumed the adsorptive nature of nanoparticles adhesion to the solid boundaries of pores. Mathematical statement of the problem was based on the modified MIM-model and Darcy – Boussinesq equations. The dependence of the desorption intensity on the value of filtration velocity was taken into account in the course of theoretical investigation. It was shown that this factor for concentration redistribution of the immobile impurity led to the steepening of the wave front as a function of time. Phenomenological realization of novel physical assumptions made the results of numerical modeling closer to the experimental data.

The process of relaxation to the mechanical and thermal equilibrium state of an insoluble surfactant film partially covering liquid has been investigated theoretically by the method of direct numerical simulation. Thermometric experimental data, which describe the film dynamics along the upper free boundary of a shallow Hele – Shaw cell, are analyzed and explained. At the initial stage, the temperature along the surface is non-uniform. This distribution generates a large-scale convective motion throughout the volume. The volume of the carrying liquid is relatively small. Therefore, the mutual action of the surfactant film and moving liquid on the dynamics of each other is turned to be significant. Thermo- and concentration-capillary forces on the surface, jointly with the buoyancy one in the volume, initiate the convection but after the heating stops, the non-monotonous propagation of the thermal front can be observed on the surface for some values of governing parameters. The calculations show that the characteristics of the motion are essentially different for temperature and concentration fields. This effect can be explained by the serious distinction of the kinetic coefficients for surfactant transfer and thermal processes.

The development of neutralization reaction during the reagent diffusion from an insoluble drop, slowly floating up in a quiescent chemically active liquid, was studied experimentally. The droplet is located in a narrow vertical gap, which causes it to take the form of a short horizontal cylinder with a free lateral surface and flat end faces. The latter circumstance allows using an interferometer to visualize the structure of the fields of reagent concentration in the droplet and the resultant products in the environment and to trace their evolution. To display the specific features of the observed phenomena, we also investigated the diffusion of a reagent from a motionless drop in a chemically active medium and diffusion of a reagent from a drop floating up in a chemically neutral liquid.

Using the example of many years of experience in cooperation between Institute No. 8 "Information Technologies and Applied Mathematics" of the Moscow Aviation Institute and Ishlinsky Institute for Problems in Mechanics of RAS points out the need for cooperation between the university and specialists of academic institutions in the preparation of highly qualified specialists in the field of CFD, stages of training, examples of qualification work and the use of software CFD products for training are presented. The difficulties of teaching CFD modeling are discussed, achievements and examples of solving the problems of hydrodynamics and heat and mass transfer by students of the Moscow Aviation Institute are given.

The theoretical problem of convection in a two-component medium (for example, in salt water) after "switching on" the sources/sinks of heat and admixture on an infinite vertical boundary is considered. Generally speaking, the degree of influence of the two components on convection is different due to the difference in their diffusion velocities. We suppose that heat diffuses much faster than the admixture and then the heated/cooled region at the lateral boundary is much thicker than the region of propagation of the impurity concentration disturbance. Therefore, convection due to temperature deviations is less affected by viscosity than due to deviations in admixture concentration. As a result, even a relatively weak "thermal" source of buoyancy can determine the direction of convection for some time in spite of the action of a more intense "concentration" source of buoyancy of a different sign. But if a vertical layer of a medium of finite thickness is considered, then a stationary regime is established over time, in which the direction of convection is determined by the total source of buoyancy, so that the direction of convection can change sign.

The authors focus on the following effect: near an inclined surface in a temperature (density) stratified turbulent medium in a gravity field, a regular flow along the slope should appear. This is due to the existence of a region of weakened turbulent exchange near the solid surface, in other words, to the appearance of spatial inhomogeneities of the effective coefficient of turbulent heat transfer. In this case, horizontal components of the gradients of temperature, density and, consequently, hydrostatic pressure arise near an inclined surface. This, in turn, it leads to the emergence of an average (non-turbulent) slope current. The mentioned problem is just an example of a much wider range of phenomena – stratified flows in the gravity field, arising due to the horizontal inhomogeneity of the transfer coefficients. In conclusion, another example of such flow is given.

The authors study the transport of solute particles in a horizontal layer of a porous medium taking into account the clogging process for a wide range of solute concentrations. On the basis of the most popular and experimentally confirmed MIM model with saturation of the immobile phase, a closed equation system describing such transport is derived. The concentration dependence of porosity is described within the Kozeny-Carman model. The criteria for the transition to the popular model of weak clogging, when the solute concentration is significantly lower than the porosity of the medium, are considered. It is shown that the basic state for the model does not correspond to the classical linear distribution of mobile solute. The convective instability of horizontal seepage with respect to two dimensional perturbations is studied. The critical curves in the space of problem parameters are obtained.

The transport process of solute in a two-dimensional liquid flow is studied. The infinite plane is "covered" by square cells with periodic conditions at its boundaries. The flow is provided by a periodic external force. If the amplitude of the external force reaches a certain critical value, then the flow in each cell contains a pair of vortices. The analysis of the transport of a passive solute in such a flow is investigated in terms of a special flow. In the framework of this approach the transport process is described by mapping functions that determine the coordinates of the particle at the end of the unit cell and the time of passage of the cell as a function of the coordinates at the entrance to the cell. These functions are obtained numerically by the random walk method taking diffusion into account. Using the special flow approach the distribution of an initially uniform distributed ensemble of passive particles with time is calculated for the passage of a long array of the unit cells. It is shown that for tiny values of diffusivity the transport slowing down some particles regarding the ensemble is observed. The speed-up of some particles regarding the ensemble is observed for moderate values of diffusivity and for high diffusivity we obtain the standard diffusion.

The diffusion coefficients of aqueous solutions of lithium, sodium, potassium, and cesium hydroxide in a concentration range of 0 to 3.0 mol/L were obtained at 25 °C and normal pressure. The Fizeau interferometer and the spatial phase-shifting method were used to measure the spatial distribution of concentration of the investigated substances. The concentration dependence of the diffusion coefficient was determined from the Matano-Boltzmann analysis. The experimental setup and techniques, as well as the image and data processing procedure, were tested using an aqueous solution of nitric acid. The comparison made for lithium, sodium, and potassium hydroxides indicated good agreement between the obtained results and the data collected from the literature. The concentration dependence of the diffusion coefficient for cesium hydroxide in water was found experimentally for the first time.

The selective frequency damping method was applied to a 90-degree bent flow. The method was used in an adaptive formulation. The most dangerous frequency was determined by solving an eigenvalue problem. It was found that one of the patterns, steady-state or pulsating, may exist at some relatively high Reynolds numbers. The periodic flow occurs due to the instability of the steady-state flow. This numerical method is easy to use but requires a great deal of time for calculations.

The paper presents the results of eddy-resolving numerical simulation of mixed convection developing in a rapidly rotating inter-disk cavity with axial throughflow of cooling air. Under conditions of the experiments available in the literature for the case of the cavity heating from the side of the disk surfaces, the computations were performed using two methods: Implicit LES and zonal RANS/ILES, with and without taking into account the gravity effects. In case of the zonal RANS/ILES approach, the axial pipe flow and the zone of turbulent mixing of throughflow with particles of heated gas were simulated on the base of the RANS equations added by a turbulence model, whereas the major part of the buoyancy-controlled cavity flow was computed with the ILES method. The ratio of the cavity width to its outer radius was 0.13. The computations were carried out at the rotational Reynolds number equal to 2·10⁵, if evaluated with the outer radius; the axial flow Reynolds number was 2·10⁴. A moderate size grid used in the computations (of about 5·10⁵ cells) provided a good resolution of quasi-laminar Ekman layers. Data on dynamics of unsteady vortex structures forming in the cavity, on characteristics of local heat transfer, as well as on effects of the gravity force action are reported. The results of computations of the time-averaged local Nusselt number on the disks surfaces are compared with measurement data; an acceptable agreement has been obtained in case of the zonal RANS/ILES approach.

The behavior of the orientation structure of a suspension of diamagnetic particles based on a cholesteric liquid crystal in an external magnetic field is theoretically studied. The effects of magnetic segregation and rigid homeotropic coupling between the liquid crystal matrix and admixture diamagnetic particles are taken into account. Within the framework of the continuum approach, a system of equations for the orientation equilibrium of the suspension was obtained using standard variational procedures. In the limit of weak magnetic fields, analytical dependences describing the behavior of the director vector field and the distribution of the admixture concentration along the suspension helix are obtained. A significant influence of the anisotropy parameter of the diamagnetic susceptibility subsystems on the wave-like concentration profiles in the suspension was revealed.

Fluid flow in non-uniform rotating (librating) cylinder with sloping ends is experimentally investigated. Periodical changes in the rotation rate lead to the appearance of inertial oscillations of the fluid. Due to the azimuthal inhomogeneity of the geometry of the ends, inertial oscillations are non-axisymmetric. The most intense pulsating motion of the fluid is observed at the frequency corresponding to the mode {1, 1, 1}, which is a global single-vortex flow. As a result of the nonlinear response, a non-axisymmetric steady flow arises along the cavity side wall.

The magnetization evolution of the paramagnetic matrix and ferromagnetic admixture ions is considered using the continuous medium model. A dynamical equation system is derived. Two possible solutions are obtained. The first is a travelling wave of finite amplitude, which is stable in the system with a ferromagnetic interaction of admixture ions. The second solution is a soliton; its amplitude and velocity are determined by the exchange energy of the admixture ions and dipole interaction between them and the bulk matrix. The dipolar coupling of the bulk lattice and admixture ions has a significant effect on the solution stability.

The authors study the effect of uniform rotation on the system of two reacting miscible liquids placed in a cylindrical Hele-Shaw cell. The cell performs a rotation with a constant velocity around the axis of symmetry resulting in a radially directed inertial field. The initial configuration of the system is statically stable and consists of two concentric layers of aqueous solutions of acid and base, which are spatially separated. When liquids are brought into contact, a neutralization reaction begins, which is accompanied by the release of salt. In this work, we obtain a system of governing equations and present the results of numerical simulation. We found that reaction-diffusion processes lead to the formation of a non-monotonic density profile with a potential well. If the rotation rate gradually increases, then a cellular convection pattern can develop in the potential well. We found that with further growth of the control parameter, the periodicity of the pattern is violated due to the influence of another convective instability, which independently develops in the domain close to the axis of rotation. The action of the inertial field results in the ejection of some convective vortices from the potential well.

The authors consider the problem of determining the stability boundary of a two-layer system of miscible liquids placed in a gravity field. Liquids are aqueous solutions of non-reacting substances with different diffusion coefficients, which are linear functions of concentrations. At the very beginning of the evolution, the solutions are separated from each other by an infinitely thin horizontal contact surface. Such a configuration can be easily realized experimentally, although it is more difficult for theoretical analysis since the base state of the system is non-stationary. Once brought into contact, the solutions begin to mix penetrating each other and creating conditions for the development of the double-diffusive instability since the initial configuration of the system is assumed to be statically stable. The problem of the convective instability of a mixture includes the equation of motion written in the Darcy and Boussinesq approximations, the continuity equation, and two transport equations for the concentrations. We apply the linearization method suggested by Wiedeburg (1890) to find a closed-form solution to the non-stationary base state problem including concentration-dependent diffusion laws for species. We derive analytical expressions for neutral stability curves and study corrections introduced by nonlinear diffusion to the stability analysis.

The interaction of bubbles with a solid flat surface of amorphous quartz, in the presence of surfactants in water, in the presence of ultrasonic action, was experimentally investigated. The study of surface properties with the use of an atomic force microscope made it possible to study the mechanism of ultrasonic degradation of the surface of solid plates, including those with surfactants adsorbed on their surface. The experiments have shown that the changes, under the action of ultrasound, of the surface properties, in these experiments, consist in the formation of chips on the surface of quartz crystals, which leads to an increase in the average surface roughness by three times in comparison with the plates that were not subjected to ultrasonic action. Was founded that the distribution of the surfactant layer on the surface of the plates depends on the concentration of the surfactant in the solution, and its presence at the solid-liquid interface leads to a decrease in the ultrasonic erosion of the plate surface. The mechanism of heterogeneous cavitation in the presence of surfactants is to reduce the probability of interaction between an inertial cavitation bubble and a solid surface, because of which the probability of local destruction of the surface decreases.

The dynamics of the interface between two immiscible liquids with a high viscosity contrast is studied experimentally under steady displacement of interface and periodic variation of the flow rate of the pumped liquid in radial Hele-Shaw cell. Classic Saffman–Taylor instability, which develops when the viscous fluid is monotonously displaced by the inviscid one, is well known. In the present work, the excitation of Saffman–Taylor instability by means of oscillations of the liquid-liquid interface is demonstrated. The interphase boundary performs axisymmetric radial oscillations at small amplitude of oscillations and in the absence of an average pumping. With the growth of the amplitude of radial oscillations the interface instability is excited, which manifests itself in the development of an azimuthally periodic finger structure during a part of the period. "Finger-like" instability is determined by the relative amplitude of the oscillations of the interphase boundary and under the conditions of the performed experiments depends neither on the oscillation frequency nor on the radial size of the interface.

The stability of a horizontal magnetic fluid layer located on a liquid substrate in the alternating magnetic field orthogonal to the surface is experimentally investigated. Kerosene-based magnetite liquid stabilized with oleic acid (ferrofluid) and perfluorooctane (to create a liquid substrate) were chosen as working fluids. The presence of a free surface and interface in the magnetic fluid layer determines the influence of spatial characteristics of the system, such as the diameter of the cell and the thickness of the liquid layer, on the resonant frequency. The stability of the ferrofluid layer in an orthogonal stationary magnetic field is investigated, and the dependence of the critical field strength on the layer thickness is obtained. The dependences of intensity amplitude on the alternating magnetic field frequency are depicted for the ferrofluid layers of various initial thicknesses. The obtained stability curves show that the low frequency field (1–4 Hz) destabilizes the system, while the high frequency one (from 4 Hz and above) has a stabilizing effect.

The effect of modulation of the cavity rotation rate on the interface of liquids of different densities and high viscosity contrast is studied experimentally. The cavity is a short horizontal cylinder rotating around its axis. The end walls of the cavity form a narrow gap. Under uniform rotation the interface has an axisymmetric shape. With the modulation growth, the axisymmetric boundary loses stability. Instability manifests itself in the appearance of a regular quasistationary relief at the interphase. The relief excitation is associated with the Kelvin-Helmholtz instability. Tangential velocity discontinuity under modulation arises due to various interaction of liquids with the cavity end walls because of viscosity contrast. The viscosity contrast, on the one hand, is responsible for tangential velocity discontinuity; on the other, it has a significant effect on the threshold of Kelvin-Helmholtz instability. It results in decrease of stability threshold and an increase of relief wavelength.

The problem of convection in a rectangular vertical cell, located in the gravity field and under the action of high-frequency vertical vibrations, is solved using the direct numerical simulation. At the initial moment of time, the system is formed by two horizontal layers of miscible liquids: the lower (heavy) layer is an aqueous solution of sodium chloride, while the upper one is a sugar solution. A two-dimensional formulation is considered; ANSYS Fluent software package is used as a solver. The impermeability and no-slip conditions are satisfied at the cell boundaries. As a result of the difference in the diffusion coefficients of dissolved species, layers with unstable stratification are formed over time near the contact zone. This leads to the onset of convection in the form of thin ascending and descending fingers. The vibrations, on average, lead to a decrease in the growth rate of fingers and the velocity of convection. In the case of relatively high vibrational overloads, a more regular convective structure forms in the diffusion layer leading to a more pronounced mixing of fluids.

The diffusion of 2-propanol vapor in the air in a channel of variable radius and in a porous medium composed of spheres of equal diameter under longitudinal oscillations is experimentally studied. In the experiments, vapor concentration at the top and bottom of the channel (or porous medium) is constant. In the absence of oscillations, mass transfer along the channel (or porous medium) is carried out due to molecular diffusion. When air oscillations are imposed, additional mass transfer effects are activated, namely, Taylor dispersion and convective mass transfer due to steady vortex flows. In the studied range of frequencies and amplitudes, the total mass transfer exceeds molecular diffusion by one order of magnitude. In a channel of variable radius, mass is transferred mainly due to the steady vortex flows (convective mass transfer) arising in the viscous boundary layer due to the inhomogeneity of the amplitude of air oscillations in narrow and wide sections of the channel. In a porous medium, Taylor dispersion plays a major role while the convective mass transfer makes minor contribution.

In this work, it is shown numerically in COMSOL Multiphysics and experimentally that a change in the NaCl concentration in water significantly affects the distribution of acoustic pressure in a laboratory sonochemical reactor. Thus, in distilled water under the action of ultrasound, two areas of increased pressure were ob-served, one of which was located directly above the ultrasound source, and the second was near the surface of the liquid, this effect is associated with the reflection of sound waves from the surface of the liquid. With the increase in the salt content, the maximum value of the acoustic pressure in the liquid decreases, which is associated with the dependence of the acoustic impedance of the liquid on the salt concentration and the peculiarities of the dynamics of vapor-gas bubbles in such solutions.

One reports experiments and numerical simulations of Faraday waves at the liquid - vapor interface of fluids (typically CO₂ and H₂) near its critical point when submitted to vibration in a weightlessness environment. It is known that in such a system striation is formed under the action of vibrations. The boundary between the liquid and gas phases is located perpendicular to the direction of vibrations, and a streaky structure in the form of periodic stripes (striations) is formed in the cavity. It is shown that under vibrations of sufficient intensity an instability develops on the striation interface perpendicular to the direction of vibrations, leading to Faraday waves. A theoretical and numerical study of this instability is carried out, the critical parameters of the appearance of Faraday waves are determined taking into account the interaction of waves on adjacent striations. Dispersion relations for Faraday waves are obtained numerically. It is shown that in the vicinity of the critical point there is a significant deviation of the dispersion relation from the classical theoretical dependence.

The joint influence of normal electric field and normal vibrations on the instability of the infinitely deep fluid dielectric layer with free boundary in the approximation of small viscosity was studied. It was shown that normal vibrations increase the value of electrical field strength exciting. The electric field effect on the first resonance zone was also studied. It was shown that for sufficiently small values of Weber number there were such values of electrical field strength that had three or two resonance zones existed instead of one first resonance zone.

Oscillatory dynamics of the liquid-liquid interface in a straight slot channel is studied experimentally. We use fluids with a large difference in viscosity and similar densities. The experimental conditions are chosen in such a way that the oscillating motion of a low-viscosity liquid is inviscid, and the oscillating motion of viscous liquid obeys Darcy's law. At the beginning of the experiment, the interface is oriented perpendicular to the channel axis. It is found that the interface takes a shape of a symmetric hill curved towards a viscous liquid under liquid oscillations. The equilibrium interface shape (the hill height) is determined by the amplitude of the interface oscillations.

This paper describes the experimental study of the mechanism of selective fixation of bubbles formed in a liquid under the influence of ultrasound on the surface of plates of various degrees of wettability when the liquid is degassed as a result of ultrasonic action. The experiments used solutions of NaCl and KCl of various concentrations, as well as distilled water. The plates are made of organic glass (wetting angle 51°) and Teflon (wetting angle 118°). As a result of the study, the experimental data on the surface area occupied by bubbles on the surface of plates were obtained, and the mechanism of selective fixation of bubbles under the influence of ultrasound in the conditions of emerging degassing was shown.

Buoyancy-driven instabilities triggered by neutralization reaction in an immiscible two-layer system placed in a vertically oriented narrow cell were studied experimentally. The initial density of the layers was always set to exclude the development of the Rayleigh-Taylor instability. The problem was examined for the surface-inactive species, namely hydrochloric acid and sodium hydroxide, which allowed studying a convective instability development solely due to buoyancy-driven mechanisms, excluding Marangoni effects. We show that one of two global scenarios develops in the system right after the layers came into contact. These scenarios, called by us diffusion-controlled and convection-controlled, essentially differ in the prevailing mechanism of mass transfer and, therefore, in the rate of reaction-diffusion-convection processes. The authors introduce the nondimensional parameter, the value of which determines the border between the two scenarios in the regime map.

Cancer cells have an altered metabolism, which results in specific kinetics of the heat localization and coherent pattern formation. Modified nonlinear Pennes equation was used for the modeling of the metabolic temperature dynamics. The numerical experiments were conducted in order to identify the tissue metabolic reactions in terms of multiscale correlation parameters (spatial invariants) as the characteristics of globally convergent dynamics of blow-up collective modes and the cancer precursor.

The stability of quasi-equilibrium of a horizontal liquid plane layer with isothermal boundaries of different temperatures, subject to circular vibrations in the horizontal plane, is experimentally studied. The rotation of the cavity around the vertical axis is set independently. In order to exclude from consideration the destabilizing effect of the gravity field, the layer is heated from the top. In the absence of rotation, the circular vibrations lead to the threshold excitation of vibrational thermal convection in the layer of nonisothermal liquid, in spite of its stable stratified in the gravity field. At given vibration amplitude and temperature difference at the layer boundaries, the threshold is determined by sharp increase in heat transfer with a monotonic increase in the vibration frequency. The size of the convective spatial structures is determined by the layer thickness. In the case of high-frequency vibrations, convection is determined by dimensionless parameters: gravitational Rayleigh number R_a and vibrational parameter R_v. The thresholds of vibrational convection excitation on the plane of these parameters in the case of circular vibrations coincide with the theoretically predicted stability boundary for linear vibrations. It is shown that rotation has a stabilizing effect on vibroconvective stability, similar to the case of gravitational convection. The threshold value of the vibration parameter R_v grows with an increase in the dimensionless rotation velocity ω_rot. Under conditions of the performed experiment, the structure of convective cells and the wave number of structures in the supercritical region do not change in comparison with ω_rot = 0.

The convection of humid and dry air was studied experimentally. The observed fluid convection involves two mechanisms of heat and mass transfer: thermal convection produced by temperature gradient and concentration convection occurred due to the inhomogeneous vapor distributions induced by evaporation and condensation of water. The convection stability of humid air was described in terms of two (thermal and concentration) Rayleigh numbers. Laboratory experiments were performed using holographic interferometry and thermocouple techniques. Experimental holograms were processed numerically in order to calculate the space distribution of the refractive index in relation to temperature and vapor concentration. The results show that the difference between moist convection and dry convection can be measured even in the absence of evaporation and condensation. The experimental interferograms for dry air (intentionally dried up to 4 % relative humidity) are given. The justification of this research requires an additional quantitative comparison with the measurements obtained for humid air (with 100 % relative humidity) undergoing the first-order phase transition of the "gas-liquid" type.

The results of calculations of the stirring rate of liquid metal in a system simulating a DC arc furnace are presented. The equations of motion and transfer of impurity were solved for the electric vortex flow of a liquid metal between two hemispherical electrodes under the influence of an external axial magnetic field. The quality of mixing was characterized by the deviation of the impurity concentration from the mean and was calculated at each time step. It is shown that the effect of an external magnetic field can both accelerate and slow down mixing. These results can be used in electrometallurgy to assess the effectiveness of electromagnetic stirring.

The effect of transverse vibrations on thermal convection in a rotating thick cylindrical fluid layer is investigated experimentally. The layer rotates about the horizontal axis of symmetry. The temperatures of the layer boundaries are different (the outer boundary is cold) and maintained constant. The study is limited to the case of fast rotation. The centrifugal force of inertia plays a stabilizing role, bringing the fluid into a state of a stable mechanical equilibrium. The vibrations affect the equilibrium of the layer in a narrow frequency range close to the rotation frequency. The structure of the convective flows is studied using PIV-method. It is found that when the frequencies of vibrations and rotation definitely coincide, the convective flow has a form of the couple of symmetric two-dimensional vortices, the position of which is stationary in the cavity reference frame. The convection occurs under the action of an induced inertial force field (superposition of vibrational and centrifugal inertial force fields). With a frequency mismatch, the induced force field rotates in the cavity reference frame. The maximum heat transport corresponds to a resonant excitation of the azimuthal two-dimensional inertial oscillations of the non-isothermal fluid layer. The convective heat transport in this case is much higher than in the case of the frequencies coincidence. The dependence of heat transport, both under resonance conditions and with equal frequencies, on vibration parameters is studied. It is shown that the centrifugal and vibrational mechanisms play a key role in the development of the convection.

In the formation of the hydrochemical regime of water bodies and adjacent territories, a significant role is played by the density stratification effects caused by the heterogeneity of the distribution of mineralization fields. When the concentration of the heavy solute is larger than one ppm under terrestrial conditions, these effects have a great influence on the nature of the flow. Such effects can not be described using hydrodynamic models within the framework of shallow water equations; for their correct description, it is necessary to use hydrodynamic models in a full three-dimensional non-hydrostatic formulation. The present paper presents the results of numerical modeling of the formation of diffuse pollution of the Vyatka River during washing of floodplain water bodies (quarries, lakes) in the region of the Kirovo-Chepetsk industrial complex. The assessment of the scale and intensity of the supply of nitrogen-containing compounds was made. The calculation results form the basis for the development of a number of possible measures aimed at both reducing diffuse runoff and ensuring the standard water quality at the main drinking water intake in Kirov, Russia.

In this paper we present the results of numerical simulation of nonlinear convection regimes of a NaCl aqueous solution heated from below. The calculations are carried out for square and horizontally elongated rectangular cavities, both in the approximation of a constant thermal diffusion coefficient and in case of taking into account its temperature dependence. Other transport coefficients are considered as constant. We observe the local and integral characteristics of the realized flows at constant and variable thermal diffusion coefficients in the conditions of the Earth and reduced gravity.

GNSS technology has made great contributions to the development of surveying and mapping in Vietnam. Many useful GNSS processing software packages have been created and widely used all over the world. However, since these software programs only have input and output, the new users without expert theoretical knowledge (especially new students) can not understand the principle or interfere with the process to obtain explicit results at each step. Therefore, the research team has built the GNSS-HUMGAdj software package to visually illustrate GNSS data processing steps for students to use. In the design stage, the group has learnt the experience in programming GNSS processing software, inheriting published GNSS data processing algorithms. In addition, some algorithms such as converted GNSS baseline in resolving the relative positioning problem, adjusting the receiver antenna height, and the effect caused by the change of distance over time were developed in the software.

The arrival of cloud computing platform Google Earth Engine (GEE) in 2010 has brought a breakthrough for analysing and processing spatial data. Applying algorithms on this platform has overcome the limitations of commercial software while processing data in building thematic databases, including land cover data. These data are a critical factor for climate change and hydrological models. This study applied Object-based Random Forest (RF) classification in the Google Earth Engine platform to produce land cover data from Landsat 8 data of the Vu Gia - Thu Bon river basin. The classification results showed 7 categories of land cover consisting of artificial forest, natural forest, paddy area, urban area, rural area, bare land, and body water, with an overall accuracy Kappa of 0.70.