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Instability of a plane horizontal layer
of an incompressible binary gas mixture
stratified in the gravity field under
the action of a transverse temperature
gradient modulated in time is studied.
The case of solid impermeable boundaries
of the layer, where the flux of matter
vanishes, is considered. The analysis is
based on the Floquet method applied to
linearized equations of convection in
the Boussinesq approximation. It is
shown that there are regions of
parametric instability at finite
frequencies. In addition to the
synchronous or subharmonic response to
an external action, the instability may
be related to quasi-periodic
disturbances. Depending on the amplitude
and frequency, modulation can stabilize
the unstable basic state and also
destabilize the equilibrium of the
fluid. The threshold values of
convection for modulations of
temperature and translational vertical
vibrations are compared.

Results of the analysis of specific features of the laminar–turbulent transition in various subsonic shear flows, which are caused by localized stationary and nonstationary streamwise structures, are presented. One mechanism of flow turbulization is considered, which involves the origination and development of secondary high-frequency disturbances in regions of flow instability generated by its modulation by streamwise structures. It is shown that this process is identical in different types of shear flows (boundary layers and jets) and in flows of the type of localized streamwise structures (stationary or nonstationary).

It is shown that during excitation of
forced, resonant, inertial oscillations
of large amplitude in a rigidly rotating
fluid, the mechanism of formation of
tornado-like vortices is primarily of a
kinematic nature (advection of
circulation of the azimuthal component
velocity and stretching of vortex lines
by the poloidal components of the
velocity field that arise from
excitation of inertial oscillations).
The main parameters of the vortices are
obtained by solutions of model problems.
To excite such oscillations, it is
necessary to deliver energy far
exceeding the initial energy of the
rotating fluid. Therefore, inertial
oscillations by themselves cannot lead
to the occurrence of intense atmospheric
vortices. Nevertheless, such
oscillations can apparently play the
role of a trigger mechanism that
activates more complex processes of
vortex formation related to instability
of the atmosphere.

Experimental estimates are obtained for
the main parameters of tornado-like
vortices that arise from excitation of
forced axisymmetric inertial
oscillations of large amplitude in a
rigidly rotating fluid.

The effect of charged dust particles on
the structure of the plasma precursor of
a strong shock wave is studied. The
conditions of formation of a weak
discontinuity front are obtained. It is
shown that resonant modes can occur in
which the concentration of dust
particles in the neighborhood of the
front increases. In the case of
positively charged particles of dust,
the formation of a localized compaction
region in the form of a soliton "bunch"
is possible and the dependence of the
amplitude of the soliton on shock-wave
velocity is nonmonotonic. In the case of
negatively charged particles of dust, a
rarefaction wave is formed. The
indicated phenomena can substantially
affect the concentration of the neutral
component in a slightly ionized plasma.

The wave structure in active bubble media in shock tubes with sudden changes of profiles in the form of "discontinuities" in cross section and a one-phase liquid waveguide is analyzed numerically. In axisymmetric formulation, the paper studies wave amplification due to reflection from a wall and focusing at the butt-end of a rigid rod aligned coaxially with the channel. In this configuration, the amplification effect results from two- dimensional cumulation of the shock wave after it leaves the annular channel and reaches the butt-end of the rod. A Mach configuration forms in the focus spot. The geometrical characteristics of the shock tube allow one to control (to some extent) the amplification coefficient and the coordinates of the focus spot. In particular, it is shown that the wave can be focused near the second discontinuity of cross section — a rigid wall (in the region of passage through the interface to the waveguide) — and intensified upon reflection. If the waveguide radius is equal to the height of the Mach stem, the reflected wave has a maximum amplitude.

The structure and dissipation of
moderate-amplitude pressure waves in a
liquid with bubbles of two dissimilar
gases (freon and helium) are
experimentally studied. It is shown that
introduction of a small (by volume)
quantity of helium bubbles with a high
thermal conductivity into a liquid with
poorly heat-conducting freon bubbles,
sharply increases the rate of damping of
solitary pressure waves.

Steady and unsteady waves propagating over the surface of a thin layer of a dilatant fluid moving over an inclined plane, with rheological properties of the fluid described by the Ostwald–de Waele power law, are studied analytically and numerically.

The physical basis of liquid-crystal
thermography, which allows visualization
and measurement of temperature and heat-
flux fields, are expounded. An
experimental technique and methods of
obtaining quantitative results are
described. Two approaches (monochromatic
and chromatic) to interpretation of
visualization data are considered.
Results illustrating the possibilities
of the method in an aerophysical
experiment are given.

The paper reports experimental results
on flow regimes with and without
cavities behind a rectangular sill in an
open channel. Photographs illustrating
the shapes of the free ends of the
cavities are given. It is shown that the
domains of existence of various flow
regimes overlap in the phase space of
problem parameters, which leads to
nonuniqueness of various functions of
the parameters. Quantitative information
is obtained for free surface profiles,
the discharge coefficient, and the
pressure on the flow bottom.