scholarly journals The shape and motion of gas bubbles in a liquid flowing through a thin annulus

2018 ◽  
Vol 855 ◽  
pp. 1017-1039 ◽  
Author(s):  
Q. Lei ◽  
Z. Xie ◽  
D. Pavlidis ◽  
P. Salinas ◽  
J. Veltin ◽  
...  
Keyword(s):  
Experimental Data ◽  
Flow Direction ◽  
Three Dimensional ◽  
Gas Bubbles ◽  
Bubble Velocity ◽  
Bubble Motion ◽  
Three Dimensional Flow ◽  
Close Match ◽  
Bubble Length ◽  
Component Parallel

We study the shape and motion of gas bubbles in a liquid flowing through a horizontal or slightly inclined thin annulus. Experimental data show that in the horizontal annulus, bubbles develop a unique ‘tadpole-like’ shape with a semi-circular cap and a highly stretched tail. As the annulus is inclined, the bubble tail tends to vanish, resulting in a significant decrease of bubble length. To model the bubble evolution, the thin annulus is conceptualised as a ‘Hele-Shaw’ cell in a curvilinear space. The three-dimensional flow within the cell is represented by a gap-averaged, two-dimensional model, which achieved a close match to the experimental data. The numerical model is further used to investigate the effects of gap thickness and pipe diameter on the bubble behaviour. The mechanism for the semi-circular cap formation is interpreted based on an analogous irrotational flow field around a circular cylinder, based on which a theoretical solution to the bubble velocity is derived. The bubble motion and cap geometry is mainly controlled by the gravitational component perpendicular to the flow direction. The bubble elongation in the horizontal annulus is caused by the buoyancy that moves the bubble to the top of the annulus. However, as the annulus is inclined, the gravitational component parallel to the flow direction becomes important, causing bubble separation at the tail and reduction in bubble length.

Three-dimensional instabilities in oscillatory flow past elliptic cylinders

2016 ◽  
Vol 798 ◽  
pp. 371-397 ◽  
Author(s):  
José P. Gallardo ◽  
Helge I. Andersson ◽  
Bjørnar Pettersen
Keyword(s):  
Circular Cylinder ◽  
Flow Direction ◽  
Three Dimensional ◽  
Circular Cylinders ◽  
Flow Structures ◽  
Three Dimensional Flow ◽  
Elliptical Cross ◽  
Dimensional Flow ◽  
Aspect Ratios ◽  
Flow Past

We investigate the early development of instabilities in the oscillatory viscous flow past cylinders with elliptic cross-sections using three-dimensional direct numerical simulations. This is a classical hydrodynamic problem for circular cylinders, but other configurations have received only marginal attention. Computed results for some different aspect ratios ${\it\Lambda}$ from 1 : 1 to 1 : 3, all with the major axis of the ellipse aligned in the main flow direction, show good qualitative agreement with Hall’s stability theory (J. Fluid Mech., vol. 146, 1984, pp. 347–367), which predicts a cusp-shaped curve for the onset of the primary instability. The three-dimensional flow structures for aspect ratios larger than 2 : 3 resemble those of a circular cylinder, whereas the elliptical cross-section with the lowest aspect ratio of 1 : 3 exhibits oblate rather than tubular three-dimensional flow structures as well as a pair of counter-rotating spanwise vortices which emerges near the tips of the ellipse. Contrary to a circular cylinder, instabilities for an elliptic cylinder with sufficiently high eccentricity emerge from four rather than two different locations in accordance with the Hall theory.

Rotational Flow Calculations in Three Dimensional Blade Passages

1982 ◽  
Author(s):  
C. Lacor ◽  
Ch. Hirsch
Keyword(s):  
Experimental Data ◽  
Solution Method ◽  
Three Dimensional ◽  
Rotational Flow ◽  
Calculation Methods ◽  
Three Dimensional Flow ◽  
Additional Function ◽  
Potential Part ◽  
Rotational Part ◽  
Element Technique

A method to calculate the three-dimensional, inviscid, rotational flow in blade passages is described. The three-dimensional flow is separated into a potential part and a rotational part. For a certain class of inlet flows, this rotational part can be described by a single additional function. The solution method can be seen as an extension of the procedure for solving the three-dimensional potential flow. The Finite Element technique is used and the method is illustrated by calculations of the flow in a rectangular elbow with 90 degrees of turning. Comparisons are made with experimental data and other calculation methods.

scholarly journals Monitoring of Indoor Airflows with a New Two-Dimensional Airflow Sensor

2019 ◽  
Vol 111 ◽  
pp. 05005
Author(s):  
Yuanchen Wang ◽  
Christian Lodroner ◽  
Michael Müller ◽  
Konstantinos Stergiaropoulos
Keyword(s):  
Control Strategies ◽  
Flow Direction ◽  
Three Dimensional ◽  
Hvac Systems ◽  
Two Dimensional ◽  
Three Dimensional Flow ◽  
Thermal Discomfort ◽  
Indoor Airflow ◽  
Dimensional Section ◽  
Airflow Sensor

Although airflow is invisible, it has a big influence on the indoor environment. An incorrectly planned HVAC systems can lead to draught and thermal discomfort in occupied zones. Since the commissioning tests required after the installation of HVAC systems are generally performed without occupancy, the tests results do not always accurately represent the airflow that occurs during ordinary usage. The airflow needs to be continuously monitored and controlled by an intelligent HVAC system. The aim of this study is to develop a new two-dimensional airflow sensor for the monitoring of indoor airflow, which can also indicate the flow direction. Several of these sensors can be placed in a planar sensor array, by which a two-dimensional section of the flow field is created. By recording data from several of these arrays simultaneously, an image of the three-dimensional flow could be acquired. The prototype of the sensor, which is made by Hahn-Schickard Society for Applied Research is currently being validated at the Institute for Building Energetics, Thermotechnology and Energy Storage. When the development is completed, it will greatly contribute to the control strategies of HVAC systems.

Behavior of Air Bubbles in an Axial-Flow Pump Impeller

1983 ◽  
Vol 105 (3) ◽  
pp. 277-283 ◽  
Author(s):  
M. Murakami ◽  
K. Minemura
Keyword(s):  
Bubble Diameter ◽  
Three Dimensional ◽  
Axial Flow ◽  
Air Bubbles ◽  
Bubble Motion ◽  
Three Dimensional Flow ◽  
Surrounding Water ◽  
Pump Impeller ◽  
Axial Flow Pump ◽  
Flow Pump

Motion of air bubbles in a high-specific-speed axial-flow pump impeller was analyzed on the basis of measured streak lines of air bubbles in the impeller. The results were compared with those obtained by a numerical solution of the bubble motion equations for three dimensional flow. Governing factors of the bubble motion are the drag force due to the surrounding water and the force due to the pressure gradient. Trajectories of the bubbles deviate somewhat from the streamlines of water, and the amount of the deviation is dependent on the bubble diameter and also on specific-speeds of the pumps and flow rate of water.

Numerical Simulation of Three-Dimensional Cavitation Around a Hydrofoil

2011 ◽  
Vol 133 (8) ◽  
Author(s):  
Jing Yang ◽  
Lingjiu Zhou ◽  
Zhengwei Wang
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Flow Field ◽  
Pressure Gradient ◽  
Three Dimensional ◽  
Side Wall ◽  
Viscosity Coefficient ◽  
Cavitation Model ◽  
Three Dimensional Flow ◽  
Shedding Frequency

Cavitation around a hydrofoil has significant three-dimensional features. The full cavitation model and a RNG k−ɛ turbulence model with a modified turbulence viscosity coefficient and which related to the vapor and liquid densities in the cavitating region were used to simulate cavitation around a hydrofoil, with emphasizing on cavity’s three-dimensional features. Computations were made on the three-dimensional flow field around a NACA66 hydrofoil at a 6 deg angle of attack. The results show that the shedding frequency on the 3D hydrofoil agrees well with the experimental data. The computed results also capture the main feature of the 3D cavitation, which had a crescent shaped cavity because of the span wise velocity. This span wise velocity is due to the span wise pressure gradient caused by the lateral vortex near the side wall of the tunnel.

scholarly journals Three-dimensional flow influences on radar layer stratigraphy

2007 ◽  
Vol 46 ◽  
pp. 22-28 ◽  
Author(s):  
G.J.-M.C. Leysinger Vieli ◽  
R.C.A. Hindmarsh ◽  
M.J. Siegert
Keyword(s):  
Accumulation Rate ◽  
Flow Direction ◽  
Three Dimensional ◽  
Flow Mode ◽  
Lateral Velocity ◽  
Three Dimensional Flow ◽  
Near Surface ◽  
Dimensional Flow ◽  
Flow Convergence ◽  
Basal Melting

AbstractVariations in the depth of radar-detectable englacial layers (isochrones) are commonly used to assess past variability in accumulation rates, but little is known about the effect of internal and basal flow variations on isochrone deflections (e.g. bumps, troughs). In this paper, we show how the isochrones are affected by such variation using a three-dimensional flow model to investigate changes in the flow mode and in increased basal melting. We also investigate how transverse flows with lateral velocity gradients affect the development of isochrones. We use the model to visualize how such variations will be seen in radar lines which cross the flow direction. We show that in the presence of lateral gradients in the flow field we can produce bumps and troughs when viewed along transects perpendicular to the flow. The model results show that the influences of flow convergence, melting and changes in flow mode, when coupled together, affect isochrones over the whole depth of the ice sheet. Finally, changes in the near-surface layers cannot be solely attributed to spatial variation in the accumulation rate; there can also be a strong signal from changes in the flow mode.

scholarly journals Numerical Simulation of the DLR-F4 Wing/Body Configuration With Wall Functions

2002 ◽  
Author(s):  
Eric Goncalves ◽  
Robert Houdeville
Keyword(s):  
Experimental Data ◽  
Numerical Simulation ◽  
Transport Equation ◽  
Flow Separation ◽  
Transonic Flow ◽  
Multigrid Method ◽  
Three Dimensional ◽  
Turbulence Models ◽  
Three Dimensional Flow ◽  
Wall Functions

This paper deals with the three-dimensional RANS computations of the transonic flow around the DLR-F4 wing-body configuration with a wall law approach. A study of the behaviour of different transport-equation turbulence models is given with comparisons to experimental data. The structure of the three-dimensional flow separation predicted by the computations is described and its topological coherence is checked. Moreover, to drastically reduce the CPU cost, a computation with a multigrid method coupled to wall functions has been tested.

Suppression of hump characteristic for a pump-turbine using leading-edge protuberance

2019 ◽  
Vol 234 (2) ◽  
pp. 187-194 ◽  
Author(s):  
Guo Zhiwei ◽  
Wang Chihang ◽  
Qian Zhongdong ◽  
Luo Xianwu ◽  
Xia Weipeng
Keyword(s):  
Experimental Data ◽  
Three Dimensional ◽  
Leading Edge ◽  
Wave Guide ◽  
Good Qualitative Agreement ◽  
Three Dimensional Flow ◽  
Pump Turbine ◽  
Guide Vanes ◽  
Pumping Mode ◽  
Dynamics Method

The application of wave guide vanes with bio-inspired leading-edge protuberances to the hump characteristic of a pump-turbine is examined in this study. Numerical simulation with a shear-stress transport turbulence model is used to calculate the three-dimensional flow in a pump-turbine in pumping mode. Three tubercle amplitudes of 0.02c, 0.04c, and 0.08c (c is chord length), and three spanwise wavenumbers (2/s, 4/s and 8/s, s is the length of span) for guide vanes are especially considered. The results obtained show that the simulated performances of original guide vanes are found to be in good qualitative agreement with experimental data, supporting the validation of the computational fluid dynamics method. For different wave guide vanes with leading-edge protuberances, it is shown that the hump characteristic of the pump-turbine in pumping mode is effectively improved. This is due to improved flow fields below the tongue in view of entropy production and vector field. The energy loss can be clearly compared through the entropy distribution for different locations of the guide vanes, and it is improved for the wave guide vanes with bio-inspired leading-edge protuberances. For current pump-turbine, the optimal amplitude and wavenumber are found to be around 0.04c and 4/s.

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