Periodical patterns (bands) developing at the interface of two immiscible fluids under vibration parallel to interface are observed under zero-gravity conditions. Fluids are slightly below their liquid-vapor critical point where they behave in a scaled, universal manner. In addition, liquid and vapor densities are close and surface tension is very low. Linear stability analyses and direct numerical simulation show that this instability, although comparable to the frozen wave instability observed in a gravity field, is nonetheless noticeably different when gravity becomes zero. In particular, the neutral curve minimum corresponds to the long-wave perturbations with $k=0$ and zero dimensionless vibrational parameter, corresponding to no instability threshold. The pattern wavelength thus corresponds to the wavelength of the perturbations with maximal growth rate. This wavelength differs substantially from the neutral perturbations wavelength at the same vibrational parameter value. The role of viscosity is highlighted in the pattern formation, with a critical wavelength dependence on vibration parameters that strongly depends on viscosity. These results compare well with experimental observations performed in the liquid-vapor phases near the critical point of $\mathrm{C}{\mathrm{O}}_2$ (in weightlessness) and ${\mathrm{H}}_2$ (under magnetic levitation).

This article is devoted to the investigation of gaseous bubble dynamics in oscillating viscous liquids of different density values. The study is conducted numerically using the level-set method with a non-stationary approach. The bubble is initially located near the upper wall of the container. The effects of the inclusion and host liquid viscosities on interaction of the bubble with the wall are analysed. The calculations show that in the absence of gravity, for low-viscosity fluids the bubble is attracted to the nearest wall, which is consistent with previous analytical and experimental results. With increasing viscosity, the vibrational attraction to the wall becomes weaker and is then replaced by repulsion, which can be explained by the decelerative effect of viscosity in the boundary layer near the rigid surface, where the average flow becomes less intensive. The dependencies of the repulsion force on the parameter values are obtained by using the balance method (investigation of the gravity level needed to attain the quasi-equilibrium state at a certain distance between the bubble and the wall). The calculations show that the repulsion force grows with decreasing Reynolds number (increase of the viscosity). This article is part of the theme issue ‘New trends in pattern formation and nonlinear dynamics of extended systems’.

Observations performed with $\mathrm{C}{\mathrm{O}}_2$ near its critical point onboard sounding rockets show that periodical patterns (bands) develop in a two-phase, liquid-vapor system under tangential vibrations in microgravity conditions. Fluids are slightly below their liquid-vapor critical point where liquid and vapor densities are close, surface tension is low, and they exhibit a scaled, universal behavior. With the increase of vibration amplitude, an instability can develop on the band pattern, leading to the appearance of Faraday waves. Theoretical and numerical investigations of the Faraday instability onset and development are carried out taking into account the interaction between the bands. The critical parameters for the onset of instability are determined. The comparisons between theoretical analysis, two-dimensional direct numerical simulation, and original experimental data show good agreement.

The effect of viscosity on the longwave Kelvin–Helmholtz instability of two immiscible incompressible fluids under horizontal vibrations is considered. The linear stability boundaries are found analytically using series expansion in terms of small wavenumber. The values of parameters, at which a transition from the longwave to finite-wavelength instability takes place, are determined. It has been shown that for high-frequency vibrations a viscous dissipation has just a weak destabilizing effect. At vibrations of moderate frequencies, destabilization is more significant, especially in the systems with large viscosity contrast. In contrast to that, at low frequencies the viscosity stabilizes the basic flow by suppressing the longwave perturbations.

This paper deals with the direct numerical simulation of quasi-stationary (frozen) wave formation at the interface of two immiscible fluids with large viscosity contrast, in a rectangular container subjected to the horizontal vibrations of finite frequency and amplitude. The critical conditions for the origination of a frozen wave as well as the dependences of the frozen wave height and wavelength on the vibration intensity are obtained. The time-evolution of the interface shape during the vibration period is analyzed. Numerical results are found to be in a good agreement with known experimental and linear stability results. The average deformation of the interface and the structure of average flows are calculated for different vibration intensities. It is shown that a change in the dependencies of the frozen wave characteristics on the vibration intensity follows a change in average flow structure.

This article deals with the reduction of dust content in the working areas of potash mines in the conditions of operating combines. This problem is topical, since the high dust concentrations in the atmosphere of dead-end drifts lead to the development of occupational diseases among miners, and traditional methods of dust control are often unsuitable for potash salts conditions. We describe the results of experimental studies carried out for the potash mine of the Verkhnekamskoye potassium-magnesium salt deposit. Next, a mathematical model of the dust–air mixture dynamics is formulated and parametrized. The Euler–Euler approach and the model of a homogeneous multicomponent medium are used. The results of a simulation for two ventilation systems (forced and exhaust) are presented. Several options for air flow rates are considered. A conclusion is reached about the most effective parameters of ventilation systems, which allows for minimizing the concentration of dust in the zone of the combine driver.