Gihun Son

EFFICIENT IMPLEMENTATION OF A COUPLED LEVEL-SET AND VOLUME-OF-FLUID METHOD FOR THREE-DIMENSIONAL INCOMPRESSIBLE TWO-PHASE FLOWS

A level-set method is combined with the volume-of-fluid method for computing incompressible two-phase flows in three dimensions, where the interface configurations are much more diverse and complicated. For efficient implementation of the coupled method, we propose geometric formulations necessary for interface reconstruction, advection of the volume fraction, and reinitialization of the level-set function. The calculation procedures are based on an explicit relation between the interface configuration and the volume fraction. This allows us to reduce the number of iterations required for reconstructing the interface. The coupled method is applied for computations of bubbles rising in a liquid and droplets adhering to a vertical wall.

A COUPLED LEVEL SET AND VOLUME-OF-FLUID METHOD FOR THE BUOYANCY-DRIVEN MOTION OF FLUID PARTICLES

A level set method is combined with the volume-of-fluid method so that the coupled method not only can calculate an interfacial curvature accurately but also can achieve mass conservation well. The coupled level set and volume-of-fluid (CLSVOF) method is applied to the buoyancy-driven motion of fluid particles. For its easy and efficient implementation, we develop a complete and efficient interface reconstruction algorithm which is based on the explicit relationship between the interface configuration and the fluid volume function. Also, a cubic-interpolated propagation (CIP) scheme is combined with the CLSVOF method to calculate the advection terms of the momentum equation accurately. The improved CLSVOF method is applied for numerical simulation of bubbles and drops rising or falling in a quiescent fluid. The numerical results are found to preserve mass conservation and to be in good agreement with the data reported in the literature.

A Level Set Method for Analysis of Film Boiling on an Immersed Solid Surface

A numerical method is presented for simulating film boiling on an immersed (or irregularly shaped) solid surface. The level set formulation for tracking the phase interfaces is modified to include the effect of phase change at the liquid–vapor interface and to treat the no-slip condition at the fluid–solid interface. The boundary or matching conditions at the phase interfaces are accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. The numerical method is tested through computations of bubble rise in a stationary liquid, single-phase fluid flow past a circular cylinder, and film boiling on a horizontal cylinder.

A Numerical Method for Bubble Motion with Phase Change

A numerical method for computing the motion of bubbles undergoing liquid?vapor phase change is presented. The method is based on a level set technique for capturing the phase interface, which is modified to include the effect of phase change at the interface as well as to achieve mass conservation during the whole calculation procedure. The modified level set method is applied for numerical simulation of bubble rise and growth in a stationary liquid. The numerical results are found to compare well with the data reported in the literature and the analytical solutions.

A LEVEL SET METHOD FOR INCOMPRESSIBLE TWO-FLUID FLOWS WITH IMMERSED SOLID BOUNDARIES

ABSTRACT A numerical method is presented for computing incompressible gas–liquid (or two-fluid) flows with immersed solid boundaries on fixed Cartesian meshes. A level set technique for tracking the gas–liquid interface is modified to treat the contact angle condition at the gas–liquid–solid interline as well as the no-slip condition at the fluid–solid interface. The no-slip condition is imposed by introducing another level set for fluid–solid phases and an effective viscosity formulation. In the immersed solid region where the level set function for gas–liquid phases is not well defined, its zero level set is calculated so that the contact angle condition should be satisfied where the three phases meet. The numerical method is validated through computations of interfacial motion subject to Taylor instability, single-fluid flow past a circular cylinder, and bubbles adhering to a cylindrical solid.

Bubble Dynamics and Heat Transfer During Nucleate Boiling in a Microchannel

The bubble dynamics and heat transfer associated with nucleate boiling in a microchannel is studied numerically by solving the equations governing conservation of mass, momentum, and energy in the liquid and vapor phases. The liquid-vapor interface is tracked by a level set method which is modified to include the effects of phase change and contact angle. Also, the method is coupled with a simple and efficient model for predicting the evaporative heat flux from the liquid microlayer. The effects of channel size, contact angle, and wall superheat on the bubble growth and heat transfer in a microchannel are investigated.

A Level-Set Method for Simulation of a Thermal Inkjet Process

A numerical approach is presented for computing a thermal inkjet process, in which bubble growth and collapse acts as a driving mechanism for ink droplet ejection. The liquid–vapor and liquid–air interfaces are tracked by a level-set method which is modified to include the effect of phase change at the liquid–vapor interface and is extended to treat the contact angle condition at an immersed solid surface. The compressibility effect of a bubble is also included in the analysis to account for the high vapor pressure caused by instantaneous bubble nucleation. The whole process of the thermal inkjet, including jet breaking, satellite droplet formation, and ink refill, as well as bubble growth and collapse, is simulated without employing a simplified bubble growth model.

A Level-Set Method for Analysis of Particle Motion in an Evaporating Microdroplet

A sharp-interface level-set (LS) method is presented for computing particle motion in an evaporating microdroplet. The LS formulation for incompressible two-phase flow is extended to include the effects of evaporation, mass transfer, heat transfer, and dynamic contact angles. A numerical technique for the conservation of particle concentration is incorporated into the LS method, and calculation procedures are also developed and tested for reducing the numerical errors caused in the computation of interface curvature and liquid–gas velocity jump. The improved LS method is applied to the simulation of particle distribution in microdroplet evaporation on a solid surface.

Bubble Dynamics, Flow, and Heat Transfer during Flow Boiling in Parallel Microchannels

Significant efforts have recently been made to investigate flow boiling in microchannels, which is considered an effective cooling method for high-power microelectronic devices. However, a fundamental understanding of the bubble motion and flow reversal observed during flow boiling in parallel microchannels is lacking in the literature. In this study, complete numerical simulations are performed to further clarify the boiling process by using the level-set method for tracking the liquid–vapor interface which is modified to treat an immersed solid surface. The effects of contact angle, wall superheat, and the number of channels on the bubble growth, reverse flow, and heat transfer are analyzed.

A Sharp-Interface Level-Set Method for Simulation of a Piezoelectric Inkjet Process

A numerical method is presented for computing the droplet motion in a piezoelectric inkjet process. The level-set method for tracking the liquid–gas interface is extended to treat the immersed (or irregular-shaped) solid surface of an ink nozzle. The no-slip condition at the fluid–solid interface as well as the matching conditions at the liquid–gas interface are accurately imposed by incorporating the ghost fluid approach based on a sharp-interface representation. The dynamic contact-angle condition at the immersed solid surface is implemented by employing a fast marching approach. The numerical method is applied to analyze the effects of nozzle shape, dynamic contact angle, and pressure pulse on the inkjet process.