The dynamics of the interface between two immiscible, low-viscosity liquids in a flat vertical cell are studied experimentally. The cell undergoes high-frequency, vertical translational vibrations. The liquids are characterized by a high-density contrast. In the absence of cell oscillations, the interface is horizontal and unperturbed. At low oscillation amplitudes, the interface oscillates together with the cell. The interface becomes unstable to the standing wave excitation when a critical amplitude is reached. A gravity-capillary standing wave oscillates at a frequency that is half that of the cell oscillations (Faraday wave). The Faraday wave is located in the plane of the cell. The height of the standing wave increases with the oscillation amplitude. It is found that the interface oscillations generate an intense steady vertical flow in the plane of the cell. Two symmetrical vortices are placed near each antinode of the wave. The height and length of the vortical pattern are consistent with the height and length of the standing wave. The fluid flows in a direction that is away from the interface at the antinodes of the standing wave and towards the interface at the nodes. The velocity of the vortical flow increases linearly with the square of the Reynolds number. Here, the Reynolds number is calculated through the amplitude of the wave oscillation velocity and the cell thickness. The phenomenon of the vortical flow excitation near the oscillating interface is of practical interest for the enhancement of the heat transfer in the cell.

Internal waves in stratified water basins are a complex physical phenomenon determined by many factors. Understanding the spatial-temporal structure of internal waves provides the basis for understanding subsequent physical, chemical, and biological processes. However, field measurements of hydrophysical characteristics such as current velocity, water temperature, and salinity can only be carried out at a few specific geographical locations. The numerical calculations allow the values of the hydrophysical characteristics at each point of the difference grid. The horizontal structure of internal waves can be determined using these data. This paper presents the results of calculating internal waves in Lake Shira based on the numerical model ROMS (Regional Ocean Modeling System) for various wind scenarios. For the model validation we compared the modeled temperatures and spectral characteristics of the velocities with measurements from monitoring stations. ROMS uses a terrain-following sigma coordinate system, so to interpret the numerical calculations, a transformation from sigma coordinates to Cartesian coordinates was carried out. It made it possible to identify the longest waves as one-node seiches. The periods of internal waves were 7 and 11 h, consequently. The linear model of a three-dimensional flow of a two-layer fluid was applied to calculate the length of the rotating seiche.

A cavitating venturi operates with an oscillating two-phase cavity that evolves through a combination of different flow mechanisms and is also closely linked to changes in geometrical configuration. Numerical prediction of the transient flow features of the venturi could become a convenient tool for venturi sizing and design for specific applications. The use of Eulerian two-phase mixture models, along with suitable cavitation models and Reynolds averaged Navier-Stokes (RANS) turbulence model, is known to over-damp the transient oscillatory nature of the cavitation zone due to the overproduction of turbulent viscosity. It is found from the literature that a modified turbulent viscosity equation formulated as a function of the two-phase density, after appropriate tuning of the model constant, is able to predict the transient phenomenon of cavitation in internal flows. However, tuning the model is highly case-specific, and generality regarding the correct frequency predictions is not always guaranteed. The current work presents the steady-state and transient numerical simulations using a two-fluid Eulerian model for the two-phase field, the Schnerr-Sauer model for cavitation and the RANS model for turbulence (without modifying the turbulent viscosity). Commercial software Ansys Fluent is used for the simulations. The model's steady-state predictability of cavitation length is benchmarked using the axisymmetric venturi data from the literature. A parametric study was also conducted to choose appropriate interfacial closure models. Systematic transient simulations were then carried out for a range of pressure ratios (Pr, the ratio of the absolute pressure at the outlet to that at the inlet of the venturi) representing the three different regions of experimentally obtained frequencies reported in the previous work of the present authors. The dynamic behavior predicted by the two-fluid modeling indicates two distinct regions of cavity oscillations. Although the numerically predicted frequencies deviate from the experimental predictions, distinct frequencies are predicted, indicating distinction in the dynamics at different pressure ratios. The current results from two-fluid models definitely provide pointers towards realistic dynamic predictions. Appropriate model improvements could offset the need for computationally expensive large eddy simulation (LES) and direct numerical simulation (DNS) models.

The transport of solute through an inclined layer of porous medium in the presence of solute particle immobilization is studied. The solute flow along the layer is generated by a constant pressure drop. The problem admits a one-dimensional filtration regime along the layer with a linear dependence of impurity distribution on coordinate across the layer. Stability of this filtration regime is investigated. Small perturbations of two types are examined: transverse and longitudinal convection rolls. As a result, stability maps are obtained for various immobilization and pumping parameters. It is shown that in case of the absence of immobilization and pumping, convection occurs monotonically. The addition of pumping affects only the stability of transverse rolls. Taking immobilization into account leads to a significant increase in the stability of the basic state, which grows with the inclination angle. It is known that when the inclination angle exceeds a threshold value, the transverse rolls become stable. We show that the value of this threshold is sensitive to the immobilization and pumping parameters. The described process can be important to design of special composite materials for heat protection with specific structure of admixture (e.g., siliconized carbon fiber or saturation of porous material by nanoparticles).

The stability of an oscillating interface between two immiscible low-viscosity liquids of different densities in a thin layer formed by two conical surfaces is experimentally studied. The symmetry axis of the cuvette is oriented along the gravity field. The oscillations of the liquids are set by a hydraulic pump to which the upper and lower outlets of the layer are connected. It is found that with an increase in the oscillation amplitude, parametric instability of the interface in the form of a standing azimuthal-periodic wave is excited. Analysis of the dispersion relation shows that the waves have a gravitational-capillary nature. The instability thresholds and supercritical wave dynamics are investigated and analyzed depending on the oscillation parameters and properties of liquids.

An experimental study of heat transfer through 10 PPI (pores per inch) copper metal foam using Al<sub>2</sub>O<sub>3</sub>-distilled water nanofluid to serve as a circulating medium is reported. The experimental work in this domain is quite rare. This paper deals with the thermal processes along with fluid flow of open-cell porous foam. The study examines the behavior of Al<sub>2</sub>O<sub>3</sub>-distilled water nanofluids by employing five different volumetric concentrations in the range from 0.1 to 0.5%, while six values of the Reynolds number are considered between 290 to 1800.The nanofluid is passed through a cavity encompassing copper metal lattice porous structure with porosity 95%. It is found that Al<sub>2</sub>O<sub>3</sub>-distilled water nanofluid is much more effective for heat transfer than distilled water. The transfer of heat is critically dependent on the concentration of the nanofluid. Heat-transfer characteristics appear to improve as concentration and Reynolds number increase. The study will be useful in development of a heat sink that employs metal foam along with nanofluid as medium for better heat dissipation in various applications, especially in the compact electronic devices.