An Improved Anti-Diffusive VOF Method to Predict Two-Fluid Free Surface Flows

2011 ◽  
Author(s):  
Y. G. Chen ◽  
W. G. Price ◽  
P. Temarel
Keyword(s):  
Free Surface ◽  
Diffusion Processes ◽  
Volume Fraction ◽  
Volume Of Fluid ◽  
Free Surface Flows ◽  
Vof Method ◽  
Advection Equation ◽  
Diffusion Term ◽  
Surface Flows ◽  
Two Fluid

This investigation continues the development of an anti-diffusive volume of fluid method [1] by improving accuracy through the addition of an artificial diffusion term, with a negative diffusion coefficient, to the original advection equation describing the evolution of the fluid volume fraction. The advection and diffusion processes are split into a set of two partial differential equations (PDEs). The improved anti-diffusive Volume of Fluid (VOF) method is coupled with a two-fluid flow solver to predict free surface flows and illustrated by examples given in two-dimensional flows. The first numerical example is a solitary wave travelling in a tank. The second example is a plunging wave generated by flow over a submerged obstacle of prescribed shape on a horizontal floor. The computational results are validated against available experimental data.

Volume of fluid methods for immiscible-fluid and free-surface flows

2008 ◽  
Vol 141 (1-3) ◽  
pp. 204-221 ◽  
Author(s):  
Vinay R. Gopala ◽  
Berend G.M. van Wachem
Keyword(s):  
Free Surface ◽  
Volume Of Fluid ◽  
Free Surface Flows ◽  
Immiscible Fluid ◽  
Surface Flows

A volume-of-fluid method for incompressible free surface flows

2009 ◽  
Vol 61 (12) ◽  
pp. 1331-1362 ◽  
Author(s):  
I. R. Park ◽  
K. S. Kim ◽  
J. Kim ◽  
S. H. Van
Keyword(s):  
Free Surface ◽  
Volume Of Fluid ◽  
Free Surface Flows ◽  
Volume Of Fluid Method ◽  
Surface Flows

scholarly journals Numerical simulation of water free-surface flows through a front-tracking lattice Boltzmann approach

2014 ◽  
Vol 17 (1) ◽  
pp. 1-6 ◽  
Author(s):  
Silvia Di Francesco ◽  
Chiara Biscarini ◽  
Piergiorgio Manciola
Keyword(s):  
Free Surface ◽  
Lattice Boltzmann ◽  
Volume Fraction ◽  
Analytical Data ◽  
Front Tracking ◽  
Free Surface Flows ◽  
Liquid Volume ◽  
Engineering Applications ◽  
Surface Flows ◽  
Practical Engineering

Three-dimensional (3D) hydraulic modelling of rapidly varying surface flows is a challenging task for practical engineering applications. One example is represented by the fast-moving fronts originating from dam breaches that proceed downstream through artificial channels. In this work, a fully 3D lattice Boltzmann method (LBM) is tested. The numerical model is a front-tracking variant of the LBM, being the free surface tracked through the liquid volume fraction. Model performances are evaluated simulating the effect of dam-break flows on synthetic settings schematically represented by an artificial domain and comparing results with analytical data and experimental laboratory measurements. Obtained results are promising for the use of LBM for practical engineering applications.

Numerical Simulation of Rayleigh-Taylor Instability With Two-Fluid Model and Interface Sharpening

2008 ◽  
Author(s):  
Luka Sˇtrubelj ◽  
Iztok Tiselj
Keyword(s):  
Free Surface ◽  
Level Set ◽  
Fluid Model ◽  
Free Surface Flows ◽  
Taylor Instability ◽  
Surface Flows ◽  
Interface Diffusion ◽  
Rayleigh Taylor Instability ◽  
Two Fluid Model ◽  
Two Fluid

The free surface flows are successfully modeled with one of the existing free surface models, such as: level set method, volume of fluid method, front tracking method, two-fluid model (two momentum equations) with modified interphase force and some others. The main disadvantage of the two-fluid model used for simulations of free surface flows is numerical diffusion of the interface, which can be significantly reduced as presented in this paper. The interface is sharpened with the conservative level set method, where after the advection step of volume fraction the numerical diffusion of the interface is reduced in such a way that the thickness of the interface is kept constant during the simulation. The reduction of the interface diffusion can also be called interface sharpening. In the present paper the two-fluid model with interface sharpening is validated with Rayleigh-Taylor instability. Under assumptions of isothermal and incompressible flow of two immiscible fluids, we simulated a system with the fluid of higher density located above the fluid of smaller density in two dimensions. Due to the gravity in the system, the fluid with a higher density moves below the fluid with a smaller density. The initial condition is not a flat interface between the fluids, but a cosine wave with small amplitude, which develops into a mushroom-like structure. Mushroom-like structure in simulation of Rayleigh-Taylor instability later develops into small droplets as result of numerical dispersion of interface (interface sharpening) or to narrow trails with interface diffusion (no interface sharpening). The results of the two-fluid model with interface sharpening are compared to two-fluid model without interface sharpening and single-fluid-model with/without interface sharpening. The analytic solution of amplitude growth can be found for small amplitudes and was also compared to simulation.

scholarly journals A Review on Hydrodynamics of Free Surface Flows in Emergent Vegetated Channels

Water ◽  
2020 ◽  
Vol 12 (4) ◽  
pp. 1218 ◽  
Author(s):  
Soumen Maji ◽  
Prashanth Hanmaiahgari ◽  
Ram Balachandar ◽  
Jaan Pu ◽  
Ana Ricardo ◽  
...  
Keyword(s):  
Free Surface ◽  
Horizontal Plane ◽  
Volume Fraction ◽  
Morphological Changes ◽  
Solid Volume Fraction ◽  
Free Surface Flows ◽  
Emergent Vegetation ◽  
Mean Flow ◽  
Surface Flows ◽  
Structure Of Flow

This review paper addresses the structure of the mean flow and key turbulence quantities in free-surface flows with emergent vegetation. Emergent vegetation in open channel flow affects turbulence, flow patterns, flow resistance, sediment transport, and morphological changes. The last 15 years have witnessed significant advances in field, laboratory, and numerical investigations of turbulent flows within reaches of different types of emergent vegetation, such as rigid stems, flexible stems, with foliage or without foliage, and combinations of these. The influence of stem diameter, volume fraction, frontal area of stems, staggered and non-staggered arrangements of stems, and arrangement of stems in patches on mean flow and turbulence has been quantified in different research contexts using different instrumentation and numerical strategies. In this paper, a summary of key findings on emergent vegetation flows is offered, with particular emphasis on: (1) vertical structure of flow field, (2) velocity distribution, 2nd order moments, and distribution of turbulent kinetic energy (TKE) in horizontal plane, (3) horizontal structures which includes wake and shear flows and, (4) drag effect of emergent vegetation on the flow. It can be concluded that the drag coefficient of an emergent vegetation patch is proportional to the solid volume fraction and average drag of an individual vegetation stem is a linear function of the stem Reynolds number. The distribution of TKE in a horizontal plane demonstrates that the production of TKE is mostly associated with vortex shedding from individual stems. Production and dissipation of TKE are not in equilibrium, resulting in strong fluxes of TKE directed outward the near wake of each stem. In addition to Kelvin–Helmholtz and von Kármán vortices, the ejections and sweeps have profound influence on sediment dynamics in the emergent vegetated flows.

Modelling of Free Surface Flow Within the Two-Fluid Euler-Euler Framework

2015 ◽  
Author(s):  
Paul Porombka
Keyword(s):  
Free Surface ◽  
Large Scale ◽  
Flow Regimes ◽  
Free Surface Flows ◽  
Two Phase Flows ◽  
Two Phase ◽  
Surface Flows ◽  
Macro Scale ◽  
Interfacial Drag ◽  
Two Fluid

Two-phase flows are regularly involved in the heat and mass transfer of industrial processes. To ensure the safety and efficiency of such processes, accurate predictions of the flow field and phase distribution by means of Computational Fluid Dynamics (CFD) are required. Direct Numerical Simulations (DNS) of large-scale two-phase flow problems are not feasible due to the computational costs involved. Therefore the Euler-Euler framework is often employed for large-scale simulations which involves macro-scale modelling of the turbulent shear stress and the interphase momentum transfer. As a long term objective, the research activities at Helmholtz-Zentrum Dresden-Rossendorf (HZDR) pursue the development of general models for two-phase flows which are based on first principles and include less empiricism. Part of this effort is focused on the development of an algebraic interfacial area density model (AIAD) which enables the simulation of two-phase flows with general morphologies including bubble, droplet and stratified flow regimes with the two-fluid approach. In this work a short overview of the AIAD model is given and recent developments are presented. The modelling of the interfacial drag in free surface flows is of particular interest and subject to ongoing research. Apart from empirical correlations, which are limited to certain flow regimes, different models for the local calculation of the interfacial drag have been developed. The latter approach is followed in the AIAD model and has recently been subject to modifications which are presented and validated as a part of this study. Furthermore, special attention is paid to the turbulence treatment at the phase boundary of free surface flows. A general damping of the gas-side turbulent fluctuations in the near interface region has been described previously in the literature but has not yet found its way into eddy viscosity turbulence models. In this work, a previously proposed damping source term for the k-ω turbulence model is validated. Model validation is performed by comparing the simulation results to experimental data in case of stratified, countercurrent air-water flow in a closed channel.

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