Vol 52, No 3 (2017)

A regular system of vortex loops in annular flow behind the edge of a disk of 6–11 cm in diameter rotating in stratified fluid is first visualized using the shadowgraph techniques (classical method with the Foucault knife and the “filament-in-focus” method). Clearly outlined vortex loops are observed in strongly and weakly stratified fluids over a wide range of the angular disk rotation velocities. The dimensions of the vortex flow region depend on the stratification (buoyancy period), the angular velocity of rotation, and the disk diameter. Extended lengthy filaments which form spiral and irregular patterns inside the loops are clearly expressed in the fine flow structure. The filaments connect the neighboring loops. The trajectories of motion of the upper edges of the loops, i.e., the sources of short internal waves, are traced.

At present, increasing attention has been concentrated on low-permeability deposits whose development is tightly related with technologies of horizontal drilling and hydraulic fracturing of the reservoir. However, the simultaneous presence of a horizontal section of the well and hydraulic fractures in the reservoir impedes the process of flow of reservoir liquids and gases through the porous medium and complicates simulation of such flows. In the present study a new analytical model of the linear inflow to a horizontal well with hydraulic fractures in low-permeability reservoirs is proposed. This is a generalizing model which takes into account both situations when there exists a linear flow in the direction perpendicular to the borehole of a horizontal well in the distant sections of the reservoir and when there is a linear flow in the direction parallel to the borehole of a horizontal well. The use of the model is not restricted by the shape of the flow domain. The new model proposed has a wide application field and does not require complex computations.

The results of the calculations and analysis of the effect of separate and joint rotation of the crystal and the crucible on the flow stability are presented for a wide range of Prandtl numbers (from 0.01 to 10). The regimes with a high stability threshold are determined for different combinations of the rotation velocities. It is shown that for high Prandtl numbers, simultaneous rotation of the crystal and the crucible makes it possible to increase the critical Grashof number in 9–12 times. A resultant diagram (map) of the limiting regimes of natural and mixed convection is constructed. Themethodology of control and analysis of 2D and 3D instability modes is discussed.

The formation and development of hydrodynamic disturbances generated by low-frequency vibrations of a local region on a flat plate behind a rectangular step in separated flow is investigated in a wind tunnel. The results are obtained at a small subsonic flow velocity using the hot-wire anemometry. It is established that the wall vibrations induce separation zone disturbances representing streaky structures accompanied by wave oscillation packets. Laminar boundary layer separation favors the wave packet growth followed by wall flow turbulization.

The results of an experimental investigation and calculations of the location of the minimum pressure point are presented for the case, when a cylindrical body moves along a wall in the presence of a small gap. The pressure on the cylindrical body surface is measured in the confusor and diffuser regions. It is shown that with decrease in the gap the minimum pressure point is displaced toward the minimum gap line, with increase in the pressure drop. An increase in the velocity of the motion at a constant gap leads only to a pressure increase in the diffuser region, while the location of the minimum pressure point remains the same. It is established that an increase in the inner cylinder radius moves the minimum pressure location away from the minimum gap line. The formation of two return flow regions in the confusor and diffuser regions near the cylindrical surface is detected. It is shown that the return flow in the pressure drop region reaches the stage of incipient cavitation bubbles. The results obtained can be useful in lubrication theory, as well as in medicine and biology.

The applicability of the criteria of existence of inviscid vortex structures (vortex Ferri singularities) is studied in the case in which a contact discontinuity of the corresponding intensity proceeds from the branching point of the λ shock wave configuration accompanying turbulent boundary layer separation under the action of an inner shock incident on the leeward wing panel. The calculated and experimental data are analyzed, in particular, those obtained using the special shadow technique developed for visualizing supersonic conical streams in nonsymmetric, Mach number 3 flow around a wing with zero sweep of the leading edges and the vee angle of 2π /3. The applicability of the criteria of existence of inviscid vortex structures is established for contact discontinuities generated by the λ shock wave configuration accompanying turbulent boundary layer separation realized under the action of a shock wave incident on the leeward wing panel. Thus, it is established that the formation of the vortex Ferri singularities in a shock layer is independent of the reason for the existence of the contact discontinuity and depends only on its intensity.

A new phenomenological model is proposed for diffusion of multicomponent gas mixtures. Obvious general structural relations between the mass diffusion fluxes and the gradients of gas mixture components are obtained within the framework of the model in the case of the multicomponent diffusion coefficients expressed in terms of the “intrinsic” diffusion coefficients of individualmixture components. The molecular mean free path model can be used to estimate the latter.