The influence of diffusion on isothermal electroconvective flow of a low- conductivity fluid under unipolar injection in the constant electric field in a plane-parallel electrode system is studied. The dependences of the space charge density and flow fields on the diffusion intensity are obtained. The diffusion coefficient of injected ions is numerically estimated for TO + I2. The results obtained are based on comparison of the numerical experiment with the available experimental data.
The characteristic feature of stratified flows in large bodies of water is generation of intense short-period internal waves at the front of long-wave disturbances. The nonlinear processes are most pronounced during the propagation of bottom and near-surface disturbances. The effective tool for studying wave processes in the ocean is the theory of multilayer shallow water with regard for the effects of nonlinearity and dispersion. It is shown that the developed mathematical models are suitable for describing the transformation of nonlinear internal waves both in the shelf zone of the sea and in the deep freshwater reservoirs. In particular, the structure of near-bottom internal waves in the shelf zone of the Sea of Japan and recently discovered near-surface internal waves in Lake Teletskoye are compared. The mechanism of generation of intense internal waves during excitation of seiche oscillations in narrow water reservoirs is discussed. Traveling waves in a multilayer fluid are constructed and numerical solutions to the nonstationary problem of generating internal waves are found. A comparison with the laboratory experiments on generation of a packet of short-period internal waves during seiche oscillations of a two-layer fluid in a long channel, as well as with the recorded near-surface internal solitary wave in Lake Teletskoye, is carried out.
In this paper, we perform direct numerical simulation of the ascent of an initially resting air bubble in water without a current. For comparison with the experiment, a complicated initial bubble shape corresponding to the experimental one is taken. Changes in the shape of the bubble during the ascent process that are obtained as a result of numerical modeling are close to experimental changes in the shape of the bubble. For comparison with the results of numerical simulations available in publications, a rising bubble with an initially spherical shape is simulated. During the ascent process, the shape of the bubble is found to be at first close to elliptical and experiences oscillations. However, then it becomes more complex: a “tail” appears in the lower part of the bubble. This mode of rising-bubble dynamics is confirmed by published results of numerical simulations.
The work is devoted to mathematical modeling of the features of the flow of fluids with a nonmonotonic dependence of the viscosity on temperature, which is inherent in some solutions and melts of polymers, as well in as a number of liquid metal alloys. For a given pressure drop, the critical conditions of heat transfer on the channel walls that determine the fluid flow rate during establishment of the flow associated with the formation of a localized high-viscosity region are found.
A numerical simulation is conducted to study the flow of a three-dimensional incompressible wall jet. The study aims to determine the jet structure and to compare the propagation mechanisms of turbulent and laminar wall jets. The numerical solution of the Navier–Stokes equations in the turbulent case is obtained using the wall-resolved large eddy simulation. The simulation results are compared to experimental data.
Numerical simulation of the receptivity of a supersonic boundary layer on a flat pointed plate with respect to model acoustic disturbances that propagate in the free-stream flow (Mach number is equal to 5) and are characteristic of the background noise of shock wind tunnels is carried out within the framework of the full Navier–Stokes equations. Spectral analysis of the perturbations induced in the boundary layer is carried out. A method for restoring the amplitude of an acoustic disturbance in free-stream flow by measuring the pressure fluctuations on the plate surface is discussed.
The phase transition in fluid flow along the ice surface with a small local irregularity at high Reynolds numbers is studied. A mathematical model that describes the phase transition dynamics based on the phase field system is constructed within the framework of the double-deck boundary layer structure. The results of numerical simulation are given.
New tests of software packages and turbulence models for validating the problems of highly intense vortex flows past structured energy-effective surfaces are presented. The idea of the testing is based on the discovery of anomalous intensification of separation flows and heat transfer in inclined grooves in plates and channel walls. At the expense of extraordinary pressure differences in the grooves, which are confirmed in experiments, swirl flows with high velocities of return and secondary currents are formed. These velocities are comparable with that of the freestream. Moreover, high-gradient zones with friction and heat removal many times higher (by a factor of from 1.5–2 to 7–9) than the friction and heat removal on a flat wall are formed. By way of illustration, we present the results of testing the VP2/3 software package developed on the basis of original muliblock computational technologies and using intersecting different-in-scale grids. The comparison of the numerical predictions with M.A. Zubin’s experiments confirmed the high static-pressure differences between the deceleration zone on the windward slope of an inclined groove and the negative pressure region at the place of tornado-like flow generation on the spherical entry segment and asserted the applicability of the RANS approach in predicting the characteristics of highly-intense swirled flows.
The regime of cavitation self-oscillations in a hydraulic system that contains a ventilated cavity with a negative cavitation number is used to create a generator of periodic impulse jets. The influence of the parameters of cavitator and output nozzle of the generator on the intensity of the impact of liquid outflowing on an obstacle (shield) located perpendicular to the direction of jet outflow is studied. It is found that increase in the nozzle length can significantly increase the efficiency of the generator, and a smooth constriction of the channel ahead of the cavitator can help to increase the operating range of the generator in the direction of larger gas blows. It is shown that there is a scale effect, namely, the relative intensity of self-oscillations decreases with increase in the liquid head pressure; however, it tends to reach a horizontal asymptote.
The reasons for the origin of narrow time-dependent currents formed in the Black Sea in the lower region of the constant pycnocline and deeper are analyzed on the basis of the results of numerical modeling. The prepositions for the generation of deep-water countercurrents in the hydrophysical fields of the Black Sea are studied with reference to the example of its north-east region, where they manifest themselves most frequently. In September 2016 and February 2017 the countercurrents in the region of the North-Caucasian coast were fixed according to the observation data of the ARGO profiling float ID6901833. On the basis of the numerical model of the Marine Hydrophysical Institute (MHI) with a 1 km-resolution and the assimilated data of the hydrological observations of the temperature and salinity the hydrophysical fields of the Black Sea are numerically simulated for the period of 2016–2017. The results of the calculations are used to reproduce the variations in the deep-water flow directions in the above-noted region and to analyze the fields of the main geophysical parameters, together with their derivative parameters. The effect of the mesoscale anticyclonic eddies and the density gradients on the velocity field structure and variability is illustrated. It is established that countercurrents propagated during several days in the anticyclonic direction, along the continental slope on the horizons from 50–100 to 500 m, and their formation took place in the conditions of the attenuation of the cyclonic Black Sea Rim Current in the upper sea layer and the intensification of the Kerch anticyclone.
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