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In the course of the search for a flow pattern optimal for culture growth in vortex bioreactors, our experiments discovered striking flow patterns that existing theoretical models cannot explain. Three immiscible liquids fill a vertical open cylindrical container whose sidewall is still, while the bottom disk rotates driving a fluid motion. The centrifugal force pushes the lower liquid (L, aqueous glycerol) from the axis to the periphery near the bottom, creating its toroid circulation that in turn drives middle liquid (M, sunflower oil) and upper liquid (U, alcoholic glycerin) circulations. With increasing rotation, counterflows develop near both interfaces LM and MU in upper fluids: the liquids move toward (away from) the axis below (above) the interface that seems paradoxical. Then, unusual topological transformations occur again in the middle liquid flow caused by competition between effects of radial friction and centrifugal forces. Near cylinder boundary at interface MU, new reverse circulation zone developed where the radial velocity became zero and then change sign. These counterintuitive results wait for their theoretical explanation and formulation of new contact conditions at the LM and MU interfaces. [ABSTRACT FROM AUTHOR]

This experimental study reveals a striking nonlinear-physics phenomenon of fundamental and practical interest—changing conditions at the interface of two swirling immiscible fluids filling a vertical cylindrical container. To this end, we use a new measurement technique significantly advanced compared with prior studies. The rotating bottom disk drives a steady axisymmetric flow of both fluids. The lower fluid makes the centrifugal circulation (CC): It spirals on toroid surfaces going to the periphery near the bottom and going back to the axis near the interface. At a slow rotation (Re = 100), the upper fluid makes the anti-centrifugal circulation. As the rotation intensifies (Re = 175), the upper-fluid flow reverses into CC near the interface-axis intersection. For strong swirl (Re = 500), the CC occurs at the entire interface. In prior studies, the spatial resolution (1 mm) was insufficient to resolve the near-interface velocity field. Here, we use the advanced (light field) measurement technique, which has significantly better resolution (0.14 mm) and clearly shows that the radial velocity at the interface is negative for small Re and becomes zero for large Re. During these metamorphoses, the topology of the lower-fluid flow remains invariant, the interface has no visible deformation, and the flow is steady and axisymmetric. [ABSTRACT FROM AUTHOR]

This experimental study reveals a curious phenomenon—hysteresis in a lab-scale two-liquid flow. The rotating bottom disk drives a toroidal circulation of water–glycerin solution (lower fluid) and sunflower oil (upper fluid) in a vertical cylindrical container. As the rotation speeds up, the solution–oil interface and the oil–air (free) surface deform rising near the sidewall and depressing near the axis as typical of whirlpools. We choose that the oil–solution volume ratio be small (having in mined oil-pollution applications) but not too small (for convenient observation). As the rotation speeds up, the oil separates from the sidewall and collects in the solution funnel. Next, the interface touches the bottom, and this is the point of no return. The centrifugal force pushes the near-bottom oil to the periphery and the buoyancy pushes oil upward. The Rayleigh–Taylor instability breaks the interface, and oil droplets disperse in the solution. If before this breakdown, the rotation starts to decrease, the oil separates from the bottom at the angular velocity ω being remarkably smaller than that for which the oil touches the bottom. Therefore, the hysteresis is a capillary-induced phenomenon. [ABSTRACT FROM AUTHOR]

This experimental study reveals a counterflow slip at the interface of two immiscible fluids filling a sealed vertical cylindrical container whose bottom disk rotates while other walls are stationary. An advanced particle image velocimetry helps us analyze and quantify streamline patterns and velocity profiles of the steady axisymmetric flows of both fluids. As the angular velocity of a disk increases, starting from zero, three changes occur in topology of the upper-fluid flow while topology of the lower-fluid flow remains invariant. These changes result in the counterflow slip at the entire interface, whose nature is speculatively discussed and requires further research. [ABSTRACT FROM AUTHOR]

This experimental and numerical study discusses the formation of double vortex breakdown in a swirling flow of two immiscible fluids where new circulation cells evolve in both fluids. The rotating lid drives the steady axisymmetric motion in a sealed vertical cylindrical container whose other walls are stationary. As the rotation intensifies, multiple topological changes occur in the flow. This study explains how two new circulation cells (vortex breakdown bubbles) almost simultaneously develop near the centers of both upper and lower fluids while the flow remains steady and axisymmetric. Such multi-cell flows can help provide fine, gentle, and nonintrusive mixing in chemical and biological reactors. [ABSTRACT FROM AUTHOR]

This experimental study reveals a spectacular and important phenomenon—double vortex breakdown—in a swirling flow of two immiscible fluids where vortex breakdown bubbles evolve simultaneously in both fluids. The rotating lid drives the steady axisymmetric motion in a sealed vertical cylindrical container whose other walls are stationary. As the rotation intensifies, topological metamorphoses occur, resulting in a multicellular flow. Two new circulation cells (vortex breakdown bubbles) simultaneously develop near the centers of both fluids while the flow remains steady and axisymmetric. Such a pattern can help provide fine, gentle, and nonintrusive mixing in chemical and biological reactors. [ABSTRACT FROM AUTHOR]

This paper describes the first experimental evidence of the vortex breakdown development in the lower fluid in a sealed vertical cylindrical container in which two immiscible fluids circulate, driven by a rotating lid. The lower fluid is water, and the upper fluid is sunflower oil. In both fluids, the rotation generates centrifugal meridional circulations separated by a thin anticentrifugal circulation layer attached to the interface from below. An advanced technique of particle image velocimetry and proper laser illumination allows for the measurement of velocity and recognition of the patterns of flow in oil and water. As the rotation speeds up, a tornadolike swirling ascending jet forms near the axis-bottom intersection. A circulation cell (vortex-breakdown bubble, VBB) then emerges near the center of the water domain, approaches the bottom, and disappears. This scenario of the appearance and disappearance of the VBB is similar to that occurring in a single-fluid flow and in the upper fluid of a two-fluid flow. [ABSTRACT FROM AUTHOR]

The article investigates the instability onset in the vortex flow in the stationary container with a rotating lid and polygonal cross-sections. Transition to unsteady flow regime is determined in closed containers with square, pentagonal and hexagonal cross-sections. The onset of flow unsteadiness is measured by combining the high spatial resolution of PIV and the temporal accuracy of LDA. A detailed transition scenario from steady and axisymmetric flow to unsteady flow with discrete rotational symmetry is investigated for the aspect ratio of 2.5 ≤ h ≤ 6.0. The results show that at steady conditions there are no asymmetric distortions of the flow topology due to the non-axisymmetric effect of the polygonal geometry of the used containers. It is found that reducing the number of cross-section angles shifts the instability onset to smaller aspect ratios and the vortex breakdown bubble stabilizes and shifts the flow instability onset to higher Reynolds numbers. The features of the flow structure formation in the polygonal containers are shown to be similar to those in the axisymmetric configuration. It is proved that the onset of the unsteadiness in polygonal configurations is based on the appearance of rotating vortex multiplets, which is similar to the cylindrical container. [ABSTRACT FROM AUTHOR]

• The development of aerial vortex bioreactors led to interest in two-fluid or multiphase flows. • The study is related to hydrodynamics and mass transfer in vortex flows for chemical and biotechnology application. • The vortex bioreactor provides the gentle mixing of ingredients required for the efficient growth of tissue cultures. • The results are of great interest for identify the kinematic parameters of opaque media of the cultured biomaterial. Research into the flow structure in an aerial vortex bioreactor is relevant for developing the methods to grow cell cultures. It is especially important in the case when, with the culture growth in the bioreactor, such parameters of the medium as density and viscosity can significantly change, accordingly altering the characteristic flow regimes. Since the cultivated culture is not transparent in most cases, it is impossible to visually determine the flow regime. Therefore, a detailed study of the regularities of flow regimes in an aerial vortex reactor is of great fundamental and applied interest. The research was carried out in an 8.5 L universal glass aerial vortex bioreactor, with a washer freely floating on its surface and stabilizing the motion of the working fluid. The regularities of the vortex motion of the culture medium depend on its volume and the rotation intensity of the activator generating vortex motion in the air. The air vortex generated by the impeller (activator) above the liquid surface spins the working fluid and a free-floating washer. The study reveals that despite the complex configuration of the flow stabilizing device (a free-floating washer), the observed vortex structure and its dynamics with increasing flow swirl intensity coincides with the structure of a confined vortex flow in a cylindrical container for both single-fluid and immiscible two-fluid configurations. [Display omitted] [ABSTRACT FROM AUTHOR]

An experimental and numerical study of a multicomponent swirl flow of a liquid in a closed cylinder is carried out for various values of the relative cylinder elongation and the Reynolds number. The experimental technique for flow characteristics measurement is based on the PIV (particle image velocimetry) technique. To study the flow characteristics in detail, we simulated the problem numerically using the Palabos and Basilisk software open-source packages. The current implementation of the Palabos package uses the LBM (lattice Boltzmann method) approach, in which the collision integral is determined by the MRT (multiple-relaxation-time) approximation, and the intercomponent interaction is established according to the Shan–Chen pseudopotential approximation. The Basilisk package uses VOF (volume-of-fluid) approach to approximate the fluid interface. In this paper, for the first time, the data considering the emergence conditions for the zone of axial isolated recirculation in a multicomponent vortex flow were obtained at different viscosity ratios of two fluids. It is shown that with a decrease in the viscosities ratio, the recirculation zone existence curve shifts closer to that corresponding to the case of a one-component flow. In the course of numerical analysis, we found that both numerical implementations of this problem describe flow characteristics with high accuracy. Both methods recreate the recirculation zone on the cylinder axis observed experimentally. However, the velocity shift on the interface is observed only in the LBM approach. [ABSTRACT FROM AUTHOR]

This experimental and numerical study of a two-fluid swirling flow reveals a discontinuity of the radial velocity at the interface. The motion is driven by the rotating lid in a sealed vertical cylindrical container. The upper fluid radially diverges near the lid, goes downward near the sidewall, converges to the axis near the interface, and rises near the axis. This centrifugal circulation drives a bulk counter-circulation of the lower fluid at a slow rotation. As the rotation intensifies, a new circulation cell emerges in the lower fluid. The numerical simulations, performed under the continuity condition for all velocity and stress components, predict that the new cell emerges near the bottom and expands upward. In contrast, the new cell emerges near the interface and expands downward in the experiment. A slip condition is proposed for the radial velocity at the interface. The slip occurs due to the centrifugal force and difference in the fluid densities. The numerical simulations, performed with the slip condition, agree with the experiment. [ABSTRACT FROM AUTHOR]

Introduction: Significant psychophysiological burdens and unhealthy lifestyle constitute the risk factors leading to students' health deterioration. Purpose: The purpose of the research was the analysis of students' health condition and lifestyle in medical university. Material and methods: The objects of the research were 100 third year students of the Faculties of General Medicine and Pediatrics of Grodno State Medical University. For the study of students' orientation on healthy lifestyle, a special scale-type questionnaire was developed and used. Results: According to the respondents' opinions it has been detected that the basic factors influencing the state of health are the lifestyle and the living conditions. The students activity is evaluated as very low as well as their rational nutrition. The majority of them smoke and drink alcohol. Conclusions: The peculiarities of studying at a medical university accompanied by imbalanced nutrition might lead to the deterioration of health in the students which are doctors to be. The results ought to lead to the optimization of prophylaxis programs and entire alteration of the students' lifestyles. [ABSTRACT FROM AUTHOR]

• Experimental study of swirling two-fluid flow in a vertical cylinder. • The rotating lid drives a steady axisymmetric circulation. • A jump of a swirl velocity at the interface is observed. • The Moffatt eddy occurs near the interface-sidewall intersection. • The results can be important for bioreactors. Recent theoretical and numerical studies predict the Moffatt eddies near the interface-wall intersection in a two-fluid flow. The current work provides the first experimental evidence of this phenomenon of fundamental interest. It also reveals a jump of the azimuthal velocity at the interface which can be important for vortex bioreactors. The rotating lid drives a two-fluid flow in a vertical cylindrical container whose other walls are stationary. Near the lid, the centrifugal force pushes the upper fluid to the sidewall thus developing its centrifugal meridional circulation. This motion drives the bulk counter-circulation and the Moffatt eddies in the lower fluid at a slow rotation. Using sunflower oil for the upper fluid, water-glycerin or alcohol-glycerin solutions for the lower fluid, and assemble averaging of PIV images allow for velocity measurement and flow visualization even in a creeping motion. This advanced experimental technique helps detect velocity jumps, occurring at the interface and the Moffatt outermost eddy. [ABSTRACT FROM AUTHOR]

Looking for an optimal flow shape for culture growth in vortex bioreactors, an intriguing and impressive structure has been observed that mimics the strong swirling flows in the atmosphere (tornado) and ocean (waterspout). To better understand the flow nature and topology, this experimental study explores the development of vortex breakdown (VB) in a lab-scale swirling flow of two immiscible fluids filling a vertical cylindrical container. The rotating bottom disk drives the circulation of both fluids while the sidewall is stationary. The container can be either sealed with the still top disk (SC) or open (OC). As the rotation strength (Re) increases, a new circulation cell occurs in each fluid—the dual VB. In case SC, VB first emerges in the lower fluid at Re = 475 and then in the upper fluid at Re = 746. In case OC, VB first emerges in the upper fluid at Re = 524 and then in the lower fluid at Re = 538. The flow remains steady and axisymmetric with the interface and the free surface being just slightly deformed in the studied range of Re. Such two-VB swirling flows can provide efficient mixing in aerial or two-fluid bioreactors. [ABSTRACT FROM AUTHOR]