Samuel W. J. Welch

Two-phase electrohydrodynamic simulations using a volume-of-fluid approach

A numerical methodology to simulate two-phase electrohydrodynamic flows under the volume-of-fluid paradigm is proposed. The electric force in such systems acts only at the interface and is zero elsewhere in the two fluids. Continuum surface force representations are derived for the electric field force in a system of dielectric-dielectric and conducting-conducting fluids. On the basis of analytical calculations for simple flow problems we propose a weighted harmonic mean interpolation scheme to smoothen the electric properties in the diffused transition region (interface). It is shown that a wrong choice of interpolation scheme (weighted arithmetic mean) may lead to a transition region thickness dependent electric field in the bulk. We simulate a set of problems with exact or approximate analytical solutions to validate the numerical model proposed. A coupled level set and volume-of-fluid (CLSVOF) algorithm has been used for simulations presented here.

Direct simulation of vapor bubble growth

Abstract This paper presents a numerical method directed towards the local simulation of axisymmetric vapor bubble growth. We use an interface tracking method in conjunction with a finite volume method on a moving unstructured mesh. We allow metastable bulk states and assume the interface exists in thermal and chemical equilibrium. The bulk fluids are viscous, conducting, and compressible. The control volume continuity, momentum and energy equations are modified in the presence of a phase interface to include surface tension and discontinuous pressure and velocity. A solid wall model is included to allow for conjugate heat transfer modes.

Application of Time-Based Fractional Calculus Methods to Viscoelastic Creep and Stress Relaxation of Materials

The quasi-static viscoelastic response of polymeric materialsis investigated utilizing constitutive models based on fractionalcalculus. Time-based fractional calculus analysis techniques areemphasized. Analytic solutions to quasi-static boundary value problemsin which the viscoelastic behavior is characterized by thefour-parameter fractional calculus-based solid model are given. Varioussets of data from the literature are fit with existing and newfractional calculus-based constitutive equations.

Planar Simulation of Bubble Growth in Film Boiling in Near-Critical Water Using a Variant of the VOF Method

A planar simulation of film boiling and bubble formation in water at 373°C, 219 bar on an isothermal horizontal surface was performed by using a volume of fluid (VOF) based interface tracking method. The complete Navier-Stokes equations and thermal energy equations were solved in conjunction with a interface mass transfer model. The numerical method takes into account the effect of temperature on the transportive thermal properties (thermal conductivity and specific heat) of vapor, effects of surface tension, the interface mass transfer and the corresponding latent heat. The computations provided a good insight into film boiling yielding quantitative information on unsteady periodic bubble release patterns and on the spatially and temporally varying film thickness. The computations also predicted the transport coefficients on the horizontal surface, which were greatly influenced by the variations in fluid properties, compared to calculations with constant properties.

Fast Volume Preservation for a Mass-Spring System

This article presents a new method to model fast volume preservation of a mass-spring system to achieve a realistic and efficient deformable object animation, without using internal volumetric meshing. With this method the simulated behavior is comparable to a finite-element-method-based model at a fraction of the computational cost

Direct simulation of film boiling including electrohydrodynamic forces

This paper presents simulations of film boiling including electrohydrodynamic forces. The coupled level-set and volume-of-fluid interface tracking method is augmented with a mass transfer model, a model for surface tension, and electrohydrodynamic force terms. The bulk fluids are perfect dielectrics—viscous, heat conducting, and incompressible. We explore film boiling on a horizontal surface and we consider the effect of an applied electric potential. The electrodynamic equation for the evolving electric field is solved in both phases during saturated horizontal film boiling, and the effects are described.

Effective Constrained Dynamic Simulation Using Implicit Constraint Enforcement

Stable and effective enforcement of hard constraints is one of the crucial components in controlling physics-based dynamic simulation systems. The conventional explicit Baumgarte constraint stabilization confines the time step to be within a stability limit and requires users to pick problem-dependent coefficients to achieve fast convergence or to prevent oscillations. The recently proposed post-stabilization method has shown a successful constraint drift reduction but it does not guarantee the physically correct behavior of motion and requires additional computational cost to decrease the constraint errors. This paper presents our new implicit constraint enforcement technique that is stable over large time steps and does not require problem dependent stabilization parameters. This new implicit constraint enforcement method uses the future time step to estimate the correct magnitude of the constraint forces, resulting in better stability over bigger time steps. More importantly, the proposed method generates physically conforming constraint forces while minimizing the constraint drifts, resulting in physically correct motion. Its asymptotic computational complexity is same as the explicit Baumgarte method. It can be easily integrated into various constrained dynamic systems including rigid body or deformable structure applications. This paper describes a formulation of implicit constraint enforcement and an accumulated constraint error and dynamic behavior analysis for comparison with existing methods.

CLSVOF method to study consecutive drop impact on liquid pool

Purpose – The purpose of this paper is to present a numerical approach for investigating different phenomena during multiple liquid drop impact on air‐water interface.Design/methodology/approach – The authors have used the coupled level‐set and volume‐of‐fluid (CLSVOF) method to explore the different phenomena during multi‐drop impact on liquid‐liquid interface. Complete numerical simulation is performed for two‐dimensional incompressible flow, which is described in axisymmetric coordinates.Findings – During drop pair impact at very low impact velocities, the process of partial coalescence is observed where the process of pinch off is different than single drop impact. At higher impact velocities, phenomena such as bubble entrapment are observed.Originality/value – In this paper, a new approach has been developed to simulate consecutive drop impact on a liquid pool.

Multimode analysis of bubble growth in saturated film boiling

The bubble formation sites in film boiling are the nodes of the instability occurring at the liquid-vapor interface. We perform a linear stability analysis with a time dependent base state, accounting for the growth of the film due to evaporation, in order to identify the most dominant wavelength. Choosing a domain size of five times the wavelength predicted by Berenson [ASME J. Heat Transfer83, 351 (1961)] and an initial liquid-vapor interface profile having a spectrum of wave numbers, we perform numerical simulations to address the effects of decay and growth of the wave numbers on bubble spacing. Numerical simulations have been performed using a coupled level set and volume of fluid algorithm.

Influence of electric field on saturated film boiling

Electrohydrodynamic (EHD) forces enhance heat and mass transfer in fluid flows. In two-phase flows under the influence of an electric field, an EHD force acts on the interface resulting in an enhanced interfacial motion. We perform a numerical study of the effect of the application of an electric field on bubble density and heat transfer characteristics during saturated film boiling. Application of electric field results in shorter bubble separation distances, faster growth of the instability, and higher bubble release frequency. Increasing the electric-field intensity shows an increase in the space averaged Nusselt number, thus indicating the role of electric field in the enhancement of heat transfer. We perform full nonlinear simulations of saturated film boiling coupled with electrohydrodynamics using a coupled level set and volume of fluid algorithm. Simulations have been performed for water and refrigerant R123a at near critical pressures.