Volume Of Fluid Simulations Research Articles

An analysis of parasitic current generation in Volume of Fluid simulations

Parasitic currents are unphysical fluid motions generated when using implementations of the Continuum Surface Force technique to model surface tension forces in Eulerian-based multi-phase Computational Fluid Dynamics calculations. In this paper, we derive and validate a correlation for the magnitude of these currents as a function of the physical and numerical parameters used in a given simulation. We find that these currents may be limited by both the inertial and viscous terms in the Navier–Stokes equations, and that they do not decrease in magnitude with increased mesh refinement or decreased computational time step. The current magnitudes that would be generated when simulating a number of common physical systems are examined, and it is found that in some circumstances their magnitude is significant.

An analysis of parasitic current generation in volume of fluid simulations

Parasitic currents are unphysical currents generated when using implementations of the Continuum Surface Force technique to model surface tension forces in multi-phase Computational Fluid Dynamics problems. We derive and validate a correlation for the magnitudes of these currents as a function of the physical and numerical parameters used in a given simulation. We find that these currents may be limited by both the inertial and viscous terms in the Navier--Stokes equations, and as observed by previous researchers, that they do not decrease in magnitude with increased mesh refinement nor decreased computational time step.

Dynamics of drop impact on solid surface: Experiments and VOF simulations

AbstractThe process of spreading/recoiling of a liquid drop after collision with a flat solid surface was experimentally and computationally studied to identify the key issues in spreading of a liquid drop on a solid surface. The long‐term objective of this study is to gain an insight in the phenomenon of wetting of solid particles in the trickle‐bed reactors. Interaction of a falling liquid drop with a solid surface (impact, spreading, recoiling, and bouncing) was studied using a high‐speed digital camera. Experimental data on dynamics of a drop impact on flat surfaces (glass and Teflon) are reported over a range of Reynolds numbers (550–2500) and Weber numbers (2–20). A computational fluid dynamics (CFD) model, based on the volume of fluid (VOF) approach, was used to simulate drop dynamics on the flat surfaces. The experimental results were compared with the CFD simulations. Simulations showed reasonably good agreement with the experimental data. A VOF‐based computational model was able to capture key features of the interaction of a liquid drop with solid surfaces. The CFD simulations provide information about finer details of drop interaction with the solid surface. Information about gas–liquid and liquid–solid drag obtained from VOF simulations would be useful for CFD modeling of trickle‐bed reactors. © 2004 American Institute of Chemical Engineers AIChE J, 51: 59–78, 2005

Scaling up Bubble Column Reactors with the Aid of CFD

Bubble column reactors, used widely in industry, often have large column diameters (up to 6 m) and are operated at high superficial gas velocities (in the range of 0.1 to 0.4 ms −1 ) in the churn-turbulent flow regime. Experimental work on bubble column hydrodynamics is usually carried out on a scale smaller than 0.3 m, at superficial gas velocities lower than 0.25 ms −1 . The extrapolation of data obtained in such laboratory scale units to the commercial scale reactors requires a systematic approach based on the understanding of the scaling principles of bubble dynamics and of the behaviour of two-phase dispersions in large scale columns. We discuss a multi-tiered approach to bubble column reactor scale up, relying on a combination of experiments, backed by Computational Fluid Dynamics (CFD) simulations for physical understanding. This approach consists of the following steps: (a) description of single bubble morphology and rise dynamics (in this case both experiments and Volume-of-Fluid (VOF) simulations are used); (b) modelling of bubble-bubble interactions, with experiments and VOF simulations as aids; (c) description of behaviour of bubble swarms and the development of the proper interfacial momentum exchange relations between the bubbles and the liquid; and (d) CFD simulations in the Eulerian framework for extrapolation of laboratory scale information to large-scale commercial reactors.

Rise characteristics of gas bubbles in a 2D rectangular column: VOF simulations vs experiments

About five centuries ago, Leonardo da Vinci described the sinuous motion of gas bubbles rising in water. We have attempted to simulate the rise trajectories of bubbles of 4, 5, 7, 8, 9, 12 and 20 mm in diameter rising in a 2D rectangular column filled with water. The simulations were carried out using the volume-of-fluid (VOF) technique developed by Hirt and Nichols ( J. Computational Physics., 39, 201–225 (1981)). To solve the Navier-Stokes equations of motion we used a commercial solver, CFX 4.1c of AEA Technology, UK. We developed our own bubble-tracking algorithm to capture “sinuous” bubble motions. The 4 and 5 mm bubbles show large lateral motions observed by Da Vinci. The 7,8 and 9 mm bubble behave like jellyfish. The 12 mm bubble flaps its wings like a bird. The extent of lateral motion of the bubbles decreases with increasing bubble size. Bubbles larger than 20 mm in size assume a spherical cap form and simulations of the rise characteristics match experiments exactly. VOF simulations are powerful tools for a priori determination of the morphology and rise characteristics of bubbles rising in a liquid. Bubble-bubble interactions are also properly modelled by the VOF technique.