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Sketch of the flow over a rotating disc with fixed cylindrical sidewall, with geometrical parameters indicated. The exact boundary condition at the air-liquid interface in the presence of a polluted interface is being questioned.
Source publication
In an experimental context, the contamination of an air–liquid interface by ambient pollutants can strongly affect the dynamics and the stability of a given flow. In some configurations, the interfacial flow can even be blocked by surface tension effects. A cylindrical free-surface flow driven by a slow rotating disc is considered here as a generic...
Contexts in source publication
Context 1
... indexation is defined as r i , θ j and z k for the radial, azimuthal and axial coordinates, respectively. For each cell C(i, j, k), the scalar quantities (i.e. the pressure P) are evaluated at the cell centre whereas the velocity components (u r , u θ , u z ) are evaluated at the centre of cell faces, see figure 10(a). For the cells adjacent to the axis, only the radial velocity component is evaluated at the axis (see figure 10b). ...
Context 2
... each cell C(i, j, k), the scalar quantities (i.e. the pressure P) are evaluated at the cell centre whereas the velocity components (u r , u θ , u z ) are evaluated at the centre of cell faces, see figure 10(a). For the cells adjacent to the axis, only the radial velocity component is evaluated at the axis (see figure 10b). The relations between the radial coordinate sets are given by ...
Citations
... Figure 6(a) indicates a kind of boundary layer in the upper fluid range 0 < z* < 10 mm where the maximal magnitude of radial velocity drops from 17 mm/s at z* = 10 mm to nearly zero at the interface (the linear extrapolation even overshoots Urm at z* = 0). This result supports the view [22] that the stress-free condition Ur/z = 0 could be replaced by Ur = 0 on the interface. In contrast, our measurements show that no boundary layer develops in the lower fluid near the interface. ...
Recent experimental studies revealed the development of slip at the interface of a steady axisymmetric swirling flow of two immiscible fluids. As swirl increases, the slip changes the flow topology scenario compared with that numerically predicted using the velocity continuity condition. This phenomenon of fundamental and practical interest has not been well understood yet. What condition should replace the velocity continuity has remained unknown. Our study addresses this problem by providing detailed experimental and numerical investigations of the flow in the interface vicinity. The bulk flow is driven by the rotating lid in a vertical cylindrical container—a model of vortex bioreactor. The centrifugal force pushes the upper fluid from the axis to the sidewall near the lid and the fluid goes back to the axis near the interface. This centrifugal circulation drives the anti-centrifugal circulation of the lower fluid at a slow rotation. As the rotation speeds up, a new flow cell emerges below the interface-axis intersection. It expands radially and downward occupying the lower-fluid domain. During these topological transformations, the flow remains steady and axisymmetric with no visible deformation of the interface. Using the advanced PIV experimental and numerical techniques, we explore the distribution of azimuthal and radial velocities in the interface vicinity and reveal that the azimuthal velocity is continuous while the radial velocity has a jump at the interface. The radial velocity tends to zero in the upper fluid. In contrast, the radial velocity does not tend to zero and satisfies the stress-free condition in the lower fluid at the interface. The numerical simulations under these conditions are in qualitative agreement with the experiment.
... The fact that the radial velocity at the interface is zero for large Re supports the view reported on the condition at the air-liquid interface. 23 However, the flows are very different. The authors 23 studied a ...
An experimental study of the cavitation flow around the NACA 0012 hydrofoil (National Advisory Committee for Aeronautics - NACA) with different surface morphology was carried out in this work. The surface morphology was set by modern laser ablation technology. The average values and intensity of vapor-gas cavities were determined. It has been revealed that laser texturing delays the emerging cavitation and somewhat decreases its intensity at higher cavitation numbers. A decrease in the cavitation number leads to an increase in its intensity for a smooth hydrofoil in comparison with a rough one, which is also expressed in an increase in the frequency of cavities. The paper presents a comparison of the flow regime with equal cavitation numbers, which clearly describes the features of the development of a vapor-gas cavity on the suction side of the foil with different surface morphology. The paper provides an explanation of the reasons for the influence of surface morphology on the development of cavities.
... Although the existence of vortices of various types has been known for a long time [3], diverse metamorphoses of vortex formation and vortex transfer of mass and energy require deeper analysis and understanding [4][5][6]. An important and interesting fact that needs additional interpretation is the formation of vortex motion during the interaction between various liquid and gaseous media (e.g., a gas vortex in an aqueous medium [7,8] and slippage in flows containing nanoparticles [9]) or immiscible liquid media differing both in density and viscosity [10]. ...
Citation: Sharifullin, B.R.; Skripkin, S.G.; Naumov, I.V.; Zuo, Z.; Li, B.; Shtern, V.N. Intense Vortex Motion in a Two-Phase Bioreactor. Water 2023, 15, 94. https://doi.org/10.3390/ w15010094 Academic Editors: Maksim Pakhomov and Pavel Lobanov Abstract: The paper reports the results of experimental and numerical studies of vortex motion in an industrial-scale glass bioreactor (volume, 8.5 L; reactor vessel diameter D, 190 mm) filled 50-80%. The model culture medium was a 65% aqueous glycerol solution with the density ρ g = 1150 kg/m 3 and kinematic viscosity ν g = 15 mm 2 /s. The methods of particle image velocimetry and adaptive track visualization allow one to observe and measure the vortex motion of the culture medium. In this work, the vortex flow investigation was performed in a practical bioreactor at the operation regimes. Our research determines not only the optimal flow structure, but also the optimal activator rotation speed, which is especially important in the opaque biological culture. The main result is that, similar to the case of two rotating immiscible liquids, a strongly swirling jet is formed near the axis, and the entire flow acquires the pattern of a miniature gas-liquid tornado. The aerating gas interacts with the liquid only through the free surface, without any mixing. This intensifies the interphase mass transfer due to the high-speed motion of the aerating gas.
... The effect of various impurities on the convective motion of water (as well as other liquids) is the subject of many past and most recent studies (see, for example, [12][13][14][15][16][17][18][19]). This is obviously due to the importance of such systems not only for industry, but also for tasks related to the environment. ...
... Which boundary condition is best for modeling heat and mass transfer near the water surface? There is currently no definitive answer in the literature [18][19][20][21]. At the same time, if the model of water heat and mass transfer corresponding to the experiment [1] is considered, this model is supplemented with the free-slip or no-slip boundary condition, and then the calculation is carried out, then it is possible to understand which of the boundary conditions better quantitatively reproduces the experimental results [1] with respect to thermal structures on the water surface. ...
The hypothesis that the previously discovered treelike thermal structures on the water surface (Phys. Fluids 34, 053112 (2022), cited below as [1]) can be explained by the presence of a surface-active impurity film is being investigated. It is shown that the simplest mathematical model of the film based on the free slip condition on the water surface, allows one to obtain previously observed structures. At the same time, the no-slip boundary condition leads to results that are inconsistent with experiment. In addition to the film, the presence of convective structures due to the horizontal and vertical temperature gradients in the water layer with an aspect ratio of about 5 is important for the appearance of treelike structures on the surface.
One of the applications that machine learning can offer to the world of Engineering and Fluid Mechanics in particular is the calibration of models making it possible to approximate the representation of a particular phenomenon. Indeed, the computational cost generated by some fluid mechanics models pushes scientists to use other models close to the original models but less computationally intensive in order to facilitate their handling. Among the different approaches used: machine learning coupled with some optimization methods and algorithms in order to reduce the computation cost induced. This paper proposes a new framework called OPTI-ENS: a new flexible, optimized and improved method, to calibrate a physical model, called the wake oscillator (WO), which simulates the vibratory behaviors of overhead line conductors. An approximation of a heavy and complex model called the strip theory (ST) model. OPTI-ENS is composed of an ensemble machine learning algorithm (ENS) and an optimization algorithm of the WO model so that the WO model can generate the adequate training data as input to the ENS model. ENS model will therefore take as input the data from the WO model and output the data from the ST model. As a benchmark, a series of Machine learning models have been implemented and tested. The OPTI-ENS algorithm was retained with a best Coefficient of determination (R2 Score) of almost 0.7 and a Root mean square error (RMSE) of 7.57e-09. In addition, this model is approximately 170 times faster (in terms of calculation time) than an ENS model without optimization of the generation of training data by the WO model. This type of approach therefore makes it possible to calibrate the WO model so that simulations of the behavior of overhead line conductors are carried out only with the WO model.
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, the upper fluid makes the anti-centrifugal circulation (AC): it spirals toward the axis near the interface and goes back to the periphery near the lid. The radial velocity is negative and continuous at the interface. As the rotation intensifies, the plenoptic measurement technique helped us to reveal an interesting and practically important phenomenon - changing the condition for the radial velocity at the interface. The velocity 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.
