Isothermal Bubble Motion Through a Rotating Liquid

1972 ◽  
Vol 94 (1) ◽  
pp. 187-192 ◽  
Author(s):  
D. L. Schrage ◽  
H. C. Perkins
Keyword(s):  
Radial Direction ◽  
Terminal Velocity ◽  
Distilled Water ◽  
Analytical Prediction ◽  
Bubble Motion ◽  
Large Pressure ◽  
Rotating Liquid ◽  
Angular Velocities ◽  
Large Pressure Gradient ◽  
Good Agreement

An analytical and experimental study of isothermal bubble motion through a liguid which is itself in motion is presented. Both analytical and experimental results are reported for the velocities and trajectories of oxygen bubbles moving through a liquid annulus which is rotating at angular velocities ranging from 500 to 1500 rpm. Results are presented for both distilled water and glycerin. The analytical prediction of the trajectories and velocities showed good agreement with the experimental data. It was found that the bubbles, which were injected at the exterior of the liquid annulus, spiralled inward rapidly and, due to the large pressure gradient in the radial direction, did not reach a constant or terminal velocity.

scholarly journals The Stationary Concentrated Vortex Model

Climate ◽  
2021 ◽  
Vol 9 (3) ◽  
pp. 39
Author(s):  
Oleg Onishchenko ◽  
Viktor Fedun ◽  
Wendell Horton ◽  
Oleg Pokhotelov ◽  
Natalia Astafieva ◽  
...  
Keyword(s):  
Vortex Structure ◽  
Radial Direction ◽  
Symmetry Axis ◽  
Outer Part ◽  
Vertical Direction ◽  
Axially Symmetric ◽  
New Model ◽  
Vortex Model ◽  
Axis Of Symmetry ◽  
Good Agreement

A new model of an axially-symmetric stationary concentrated vortex for an inviscid incompressible flow is presented as an exact solution of the Euler equations. In this new model, the vortex is exponentially localised, not only in the radial direction, but also in height. This new model of stationary concentrated vortex arises when the radial flow, which concentrates vorticity in a narrow column around the axis of symmetry, is balanced by vortex advection along the symmetry axis. Unlike previous models, vortex velocity, vorticity and pressure are characterised not only by a characteristic vortex radius, but also by a characteristic vortex height. The vortex structure in the radial direction has two distinct regions defined by the internal and external parts: in the inner part the vortex flow is directed upward, and in the outer part it is downward. The vortex structure in the vertical direction can be divided into the bottom and top regions. At the bottom of the vortex the flow is centripetal and at the top it is centrifugal. Furthermore, at the top of the vortex the previously ascending fluid starts to descend. It is shown that this new model of a vortex is in good agreement with the results of field observations of dust vortices in the Earth’s atmosphere.

scholarly journals Kinetic ballooning modes in tokamaks and stellarators

2018 ◽  
Vol 84 (6) ◽  
Author(s):  
K. Aleynikova ◽  
A. Zocco ◽  
P. Xanthopoulos ◽  
P. Helander ◽  
C. Nührenberg
Keyword(s):  
Plasma Pressure ◽  
Analytical Prediction ◽  
Ion Temperature ◽  
Ion Temperature Gradient ◽  
Large Pressure ◽  
Equilibrium Configurations ◽  
Mhd Stability ◽  
Ideal Magnetohydrodynamic ◽  
General Geometry ◽  
The Ideal

Kinetic ballooning modes (KBMs) are investigated by means of linear electromagnetic gyrokinetic (GK) simulations in the stellarator Wendelstein 7-X (W7-X), for high-$\unicode[STIX]{x1D6FD}$ plasmas, where $\unicode[STIX]{x1D6FD}$ is the ratio of thermal to magnetic plasma pressure. The analysis shows suppression of ion-temperature-gradient (ITG) and trapped particle modes (TEM) by finite-$\unicode[STIX]{x1D6FD}$ effects and destabilization of KBMs at high $\unicode[STIX]{x1D6FD}$. The results are compared with a generic tokamak case. We show that, for large pressure gradients, the frequency of KBMs evaluated by the GENE code is in agreement with the analytical prediction of the diamagnetic modification of the ideal magnetohydrodynamic limit in W7-X general geometry. Thresholds for destabilization of the KBM are predicted for different W7-X equilibrium configurations. We discuss the relation of these thresholds to the ideal magnetohydrodynamic (MHD) stability properties of the corresponding equilibria.

Analytical Prediction of the Unsteady Lift on a Rotor Caused by Downstream Struts

1987 ◽  
Author(s):  
A. C. Taylor ◽  
W. F. Ng
Keyword(s):  
Flow Field ◽  
Rotor Blades ◽  
Experimental Measurements ◽  
Analytical Prediction ◽  
Two Dimensional ◽  
Turbomachinery Blades ◽  
Downstream Flow ◽  
Good Agreement ◽  
Flow Obstructions ◽  
Unsteady Lift

A two-dimensional, inviscid, incompressible procedure is presented for predicting the unsteady lift on turbomachinery blades caused by the upstream potential disturbance of downstream flow obstructions. Using the Douglas-Neumann singularity superposition potential flow computer program to model the downstream flow obstructions, classical equations of thin airfoil theory are then employed, to compute the unsteady lift on the upstream rotor blades. The method is applied to a particular geometry which consists of a rotor, a downstream stator, and downstream struts which support the engine casing. Very good agreement between the Douglas-Neumann program and experimental measurements was obtained for the downstream stator-strut flow field. The calculations for the unsteady lift due to the struts were in good agreement with the experiments in showing that the unsteady lift due to the struts decays exponentially with increased axial separation of the rotor and the struts. An application of the method showed that for a given axial spacing between the rotor and the strut, strut-induced unsteady lift is a very weak function of the axial or circumferential position of the stator.

On bubble motion in a rotating liquid under simulated low and zero gravity

1976 ◽  
Vol 45 (5-6) ◽  
pp. 307-315 ◽  
Author(s):  
J. Siekmann ◽  
W. Johann
Keyword(s):  
Zero Gravity ◽  
Bubble Motion ◽  
Rotating Liquid

Measurements of the Terminal Velocity of Bubbles Rising in a Chain

1973 ◽  
Vol 95 (1) ◽  
pp. 17-22 ◽  
Author(s):  
C. H. Marks
Keyword(s):  
Bubble Size ◽  
Tap Water ◽  
Bubble Radius ◽  
Terminal Velocity ◽  
Bubble Velocity ◽  
Distilled Water ◽  
Rise Velocity ◽  
Sugar Water ◽  
A Chain ◽  
Made In

Measurements were made of the effect of frequency of formation on the velocity of air bubbles rising in a chain through distilled water, lap water, and sugar water. In all cases, increasing the frequency increased the rise velocity for a given bubble size. Measurements made in distilled water showed that the increase of velocity with frequency dropped off with bubble size until it was negligible for the smaller bubbles. It was shown that the variation of bubble velocity with frequency and size can be fairly well correlated with the velocity of rise of solitary bubbles by means of a model based on turbulent wake theory. Tap-water measurements showed the same effect of impurities in the water on the bubble rise velocity as had been observed for solitary bubbles; however, the bubble radius at which the effect became apparent decreased with frequency. Measurements made in sugar water showed that the effect of fluid properties on the rise velocity decreased as frequency increased. At the highest frequencies, no difference could be seen between the distilled water and the sugar water rise velocity curves.

Transport of Non-Spherical Particles in Turbulence: Application of the LBM

2006 ◽  
Author(s):  
Andreas Ho¨lzer ◽  
Martin Sommerfeld
Keyword(s):  
Angular Velocity ◽  
Turbulent Flow ◽  
Radial Direction ◽  
Stokes Number ◽  
Spherical Particles ◽  
Axis Ratio ◽  
Angular Velocities ◽  
Boltzmann Method ◽  
Short Time ◽  
Cylindrical Particles

Direct numerical simulations of the motion of volume equivalent single cylindrical particles with axis ratios of 1, 2, 3, and 4 and Stokes numbers of 1, 2, 4, and 40 in a homogeneous isotropic turbulent flow field are presented. The forced turbulent flow is simulated using the Lattice Boltzmann Method (LBM). It is observed that the rms velocity and the rms angular velocity in longitudinal and in radial direction are identical for every particle, even though the rms forces can differ more than 100% and the rms torque more than 1000% in both directions. However, these differences in force and torque result in a different short-time behaviour of the particle in longitudinal and in radial direction. The rms particle velocity is found to decrease with increasing axis ratio and the rms particle angular velocity to have a maximum at an axis ratio of about 2.5. The ratio of the rms velocity of the particle to that of the fluid decreases with increasing Stokes number as well as the ratio between the rms angular velocities, as one could expect.

Evaluation of the Mixing Performance of the Micromixers With Grooved or Obstructed Channels

2008 ◽  
Vol 130 (7) ◽  
Author(s):  
Yeng-Yung Tsui ◽  
Ching-Shiang Yang ◽  
Chung-Ming Hsieh
Keyword(s):  
Vertical Plane ◽  
Pressure Head ◽  
Fluid Mixing ◽  
Mixing Performance ◽  
Large Pressure ◽  
Fluid Concentration ◽  
Speed Up ◽  
Periodic Configuration ◽  
The Cost ◽  
Good Agreement

The mixing flows in microchannels were examined using numerical methods. To speed up fluid mixing, it is essential to generate lateral transport of mass. In this study, the mixing flow is disrupted by either placing grooves or block obstacles on the walls of the channels. Since the grooves or the blocks appear in a periodic configuration, the velocity is solved only in a section of the channel. With the repeating cycle of flow velocity field, the fluid concentration can be calculated throughout the entire length of the channel. Good agreement with experiments in the mixing performance justifies the present methodology. Two different channel configurations are under consideration: grooved channels and obstructed channels. The results reveal that with straight grooves, a well organized vortex flow is formed in the vertical plane along the groove, which leads to a helical flow in the channel. The mixing performance can be enhanced by having grooves on both the top and the bottom walls arranged in a staggered manner, by which the transversal velocity is largely increased. It is seen that the strength of the secondary flow and, thus, the mixing can be improved by suitably choosing geometric parameters of the groove, such as the depth, the width, and the oblique angle. It is also shown that the efficient mixing for the staggered herringbone type groove is due to the fluid stratification caused by the exchange of position of the resulted counter-rotating vortices. As for the obstructed channels, the flows are in essence two dimensional. Very strong transversal velocity can be produced by narrowing down the flow passage in the channel. However, the efficient mixing is obtained at the cost of large pressure head loss.

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