A Numerical Study of Dynamic Meniscus

2002 ◽  
Author(s):  
C. S. L. Liu ◽  
S. H.-K. Lee
Keyword(s):  
Free Surface ◽  
Numerical Study ◽  
Contact Point ◽  
Air Entrainment ◽  
Dynamic Contact ◽  
Surface Flow ◽  
Coating Material ◽  
Coating Process ◽  
Coating Flow ◽  
Phase Calculation

Air entrainment is one of the bottlenecks during high speed coating process. Numerous studies concerned with the mechanics of air entrainment in coating process have been reported during the last four decades. The difficulty in visualization of three-phase contact point due to small dimension made it a hard task to unveil the mechanism of air entrainment experimentally. In most numerical studies on free surface flow, the effect of air upon dynamic meniscus was usually neglected, which induced the coarse accuracy in air entrainment study. In the present study, the numerical simulation of free surface coating flow as well as airflow upon dynamic meniscus was given. The effect of several parameters, such as coating material viscosity, and coating cup geometry, especially airflow upon free surface on the dynamic meniscus, was studied. The results showed that the dynamic effects of air in the vicinity of dynamic meniscus should not be disregarded. The pressure near the dynamic meniscus, especially at the dynamic contact point in the coating flow simulation, was much smaller than the atmosphere pressure, while in the gas phase calculation, the value was larger than the atmosphere one at the same position. These results indicated another explanation of the mechanics of air entrainment: the low pressure in the vicinity of dynamic contact point in the liquid makes the gas dissolve easily into the coating material, and the gas flow will even break the dynamic meniscus when the pressure difference between the gas and liquid phase is large enough. The effects of several factors on pressure distribution at the dynamic meniscus were also presented.

scholarly journals Experiments and Simulations of Free-Surface Flow behind a Finite Height Rigid Vertical Cylinder

Fluids ◽  
2021 ◽  
Vol 6 (10) ◽  
pp. 367
Author(s):  
Valentin Ageorges ◽  
Jorge Peixinho ◽  
Gaële Perret ◽  
Ghislain Lartigue ◽  
Vincent Moureau
Keyword(s):  
Free Surface ◽  
Numerical Study ◽  
Three Dimensional ◽  
Vertical Cylinder ◽  
Free Surface Flow ◽  
Air Entrainment ◽  
Surface Flow ◽  
Finite Height ◽  
Wave Patterns ◽  
Different Diameters

We present the results of a combined experimental and numerical study of the free-surface flow behind a finite height rigid vertical cylinder. The experiments measure the drag and the wake angle on cylinders of different diameters for a range of velocities corresponding to 30,000 <Re< 200,000 and 0.2<Fr<2 where the Reynolds and Froude numbers are based on the diameter. The three-dimensional large eddy simulations use a conservative level-set method for the air-water interface, thus predicting the pressure, the vorticity, the free-surface elevation and the onset of air entrainment. The deep flow looks like single phase turbulent flow past a cylinder, but close to the free-surface, the interaction between the wall, the free-surface and the flow is taking place, leading to a reduced cylinder drag and the appearance of V-shaped surface wave patterns. For large velocities, vortex shedding is suppressed in a layer region behind the cylinder below the free surface. The wave patterns mostly follow the capillary-gravity theory, which predicts the crest lines cusps. Interestingly, it also indicates the regions of strong elevation fluctuations and the location of air entrainment observed in the experiments. Overall, these new simulation results, drag, wake angle and onset of air entrainment, compare quantitatively with experiments.

A Numerical Investigation of the Free Surface Flow During Optical Fiber Coating Process

2001 ◽  
Author(s):  
C. S. L. Liu ◽  
S. H.-K. Lee
Keyword(s):  
Contact Angle ◽  
Free Surface ◽  
Optical Fiber ◽  
Dynamic Contact Angle ◽  
Air Entrainment ◽  
Dynamic Contact ◽  
Coating Process ◽  
Coating Quality ◽  
Fiber Coating ◽  
Drawing Speed

Abstract Optical fiber has increasingly played a crucial role in the information transmission area nowadays. The elevated demand makes it necessary to manufacture high quality light-guide fibers that have proper mechanical properties to endure the stresses induced during installations and operations. Optical fiber coating process provides a protection layer to shield the fiber from surface abrasion and also to increase the fiber’s tensile strength. However, there are problems encountered during this process which reduce the coating quality. One of the major problems is air entrainment, which may lead to eccentrical or incomplete coating. Apparently, it is of great interest to study this problem to improve the coating quality. Many experimental studies have been performed on the dynamic contact angle, air entrainment velocity and their correlation with various parameters, such as the viscosity and the surface tension of coating materials, fiber drawing speed, etc. Nevertheless, how the coating flow affects the upper meniscus (directly related with dynamic contact angle and air entrainment) has not been intensively studied. Understanding of the effects is essential to improve the coating quality. To fulfill this requirement, the present work focused on investigating the relation of upper meniscus and fiber drawing speed. This is just the first part of the serial study on the optical fiber coating process. Firstly, a numerical code was developed with finite volume formulation. The results showed that the code had the capacity to deal with this free surface fluid flow problem. The simulated free surface shape was validated with experimental data available. The trend of the upper meniscus shape and dynamic contact angle developments at high drawing velocity was simulated. The results showed, as expected, that the dynamic contact angle would approach 180° with the increase of the fiber-drawing speed.

Nonlinear free-surface flow due to an impulsively started submerged point sink

1998 ◽  
Vol 364 ◽  
pp. 325-347 ◽  
Author(s):  
MING XUE ◽  
DICK K. P. YUE
Keyword(s):  
Free Surface ◽  
Steady State ◽  
Numerical Study ◽  
Free Surface Flow ◽  
Small Time ◽  
Surface Flow ◽  
Boundary Integral ◽  
Critical Regime ◽  
Gravitational Acceleration ◽  
Nonlinear Free Surface

The unsteady fully nonlinear free-surface flow due to an impulsively started submerged point sink is studied in the context of incompressible potential flow. For a fixed (initial) submergence h of the point sink in otherwise unbounded fluid, the problem is governed by a single non-dimensional physical parameter, the Froude number, [Fscr ]≡Q/4π(gh5)1/2, where Q is the (constant) volume flux rate and g the gravitational acceleration. We assume axisymmetry and perform a numerical study using a mixed-Eulerian–Lagrangian boundary-integral-equation scheme. We conduct systematic simulations varying the parameter [Fscr ] to obtain a complete quantification of the solution of the problem. Depending on [Fscr ], there are three distinct flow regimes: (i) [Fscr ]<[Fscr ]1≈0.1924 – a ‘sub-critical’ regime marked by a damped wave-like behaviour of the free surface which reaches an asymptotic steady state; (ii) [Fscr ]1<[Fscr ]<[Fscr ]2≈0.1930 – the ‘trans-critical’ regime characterized by a reversal of the downward motion of the free surface above the sink, eventually developing into a sharp upward jet; (iii) [Fscr ]>[Fscr ]2 – a ‘super-critical’ regime marked by the cusp-like collapse of the free surface towards the sink. Mechanisms behind such flow behaviour are discussed and hydrodynamic quantities such as pressure, power and force are obtained in each case. This investigation resolves the question of validity of a steady-state assumption for this problem and also shows that a small-time expansion may be inadequate for predicting the eventual behaviour of the flow.

scholarly journals Free surface profile and inception point as characteristics of aerated flow over stepped spillway: Numerical study

2019 ◽  
Vol 42 (1) ◽  
pp. 42-48
Author(s):  
Chakib Bentalha ◽  
Mohammed Habi
Keyword(s):  
Free Surface ◽  
Kinetic Energy ◽  
Water Depth ◽  
Numerical Study ◽  
Surface Profile ◽  
Air Entrainment ◽  
Stepped Spillway ◽  
Ansys Fluent ◽  
Vof Model ◽  
Inception Point

Abstract Stepped spillway is hydraulic structure designed to dissipate the excess in kinetic energy at the downstream of dams and can reduce the size of stilling basin at the toe of the spillway or chute. The flow on a stepped spillway is characterised by the large aeration that can prevent or reduce the cavitation damage. The air entrainment starts where the boundary layer attains the free surface of flow; this point is called “point of inception”. Within this work the inception point is determined by using software Ansys Fluent where the volume of fluid (VOF) model is used as a tool to track the free surface thereby the turbulence closure is derived in the k − ε turbulence standard model. This research aims to find new formulas for describe the variation of water depth at step edge and the positions of the inception point, at the same time the contour map of velocity, turbulent kinetic energy and strain rate are presented. The found numerical results agree well with experimental results like the values of computed and measured water depth at the inception point and the numerical and experimental inception point locations. Also, the dimensionless water depth profile obtained by numerical method agrees well with that of measurement. This study confirmed that the Ansys Fluent is a robust software for simulating air entrainment and exploring more characteristics of flow over stepped spillways.

Dynamic Contact Angle of Modified Biopolymer Droplet on Urea Surface: Temperature Effects

2013 ◽  
Vol 594-595 ◽  
pp. 566-570 ◽  
Author(s):  
Yon Norasyikin Samsudin ◽  
Ku Zilati Ku Shaari ◽  
Zakaria Man ◽  
Suriati Sufian
Keyword(s):  
Contact Angle ◽  
High Speed ◽  
Dynamic Contact Angle ◽  
Ccd Camera ◽  
Dynamic Contact ◽  
Droplet Impact ◽  
Coating Material ◽  
Coating Process ◽  
Fluidised Bed ◽  
Impact Behaviour

The droplet impact behaviour provides the particle coating characterization during the coating process of controlled release fertiliser. To have a good coating uniformity around the urea granules, it is necessary to enhance the wettabitily properties between the coating material and urea surface. The biopolymer material is preferred as the coating material because this polymer may degrade and will not cause any environmental impact to the environment. Various compositions of starch/urea /borate/lignin were prepared and evaluated for the wettability properties. The wettability characteristic measured is the dynamic contact angle. The high speed Charged-Couple Device (CCD) camera was used to capture the images of this droplet impact behaviour. Temperature plays an important factor during wetting stage because the coating material must be completely dried in continuous coating process in fluidised bed. From this analysis, it indicates that a composition of starch/urea/ borate (50/15/2.5) with 10% lignin has the best wettability characteristic and thus suitable to be used as a coating material. The ideal temperature for the coating process is 60°C.

scholarly journals Free-Surface Flow Over River Bottom Sill: Experimental and Numerical Study

2015 ◽  
Vol 2 (S1) ◽  
pp. 133-139 ◽  
Author(s):  
Evangelia D. Farsirotou ◽  
Spiridon I. Kotsopoulos
Keyword(s):  
Free Surface ◽  
Numerical Study ◽  
Free Surface Flow ◽  
Surface Flow ◽  
River Bottom

scholarly journals Numerical Simulation of Free Surface Flow on Spillways and Channel Chutes with Wall and Step Abutments by Coupling Turbulence and Air Entrainment Models

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3036
Author(s):  
Le Thi Thu Hien ◽  
Duong Hoai Duc
Keyword(s):  
Free Surface ◽  
Free Surface Flow ◽  
Air Entrainment ◽  
Surface Flow ◽  
Navier Stokes ◽  
Eddy Simulation ◽  
Optimal Distance ◽  
Large Eddy ◽  
Flow Through ◽  
Turbulent Models

Spillways and channel chutes are widely used in hydraulic works. Two kinds of abutment—walls and steps—are usually constructed to dissipate energy; however, they may also cause cavitation at the abutment position. In this study, we used Flow 3D with the Reynolds-averaged Navier–Stokes (RANS) and large eddy simulation (LES) turbulent models which included air entrainment to simulate the free surface flow through the spillway, channel chute and stilling basin of the Ngan Truoi construction to optimize the configuration of walls and dams. We measured the water level, velocity and pressure to estimate the influence of grid size and the turbulent model type used. Our results highlight the need to include air entrainment in the model simulating rapid flow over a hydraulic construction. With adjustments for energy loss, this study shows that walls provide the best results and the optimal distance between two walls is 2.8 m.

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