Keynote Talk 10
Wednesday, January 6, 2010 / 09:30 – 10:15 hrs
Fine Scale Modeling and Simulation of Multiphase and Phase Separating Flows
Sanjoy Banerjee
Distinguished Professor of Chemical Engineering,
Director, The CUNY Energy Institute,
The City College New York,
CUNY, NY 10031, USA.
banerjee@che.ccny.cuny.edu
ABSTRACT
Multiphase flows play a central role in problems related to operation and safety of nuclear plants. Common, but significant, features of such problems are complex geometries and topography, transport processes across phase boundaries, and internal interfaces that merge, break, and deform. Requirements to predict fluid motion under such conditions provide significant challenges for computational fluid dynamics, particularly for direct simulation of flows involving internal interfaces. In this paper, we will focus on two models that capture the motion of internal interfaces implicitly and can resolve complex flows down to computational grid sizes. The first method is based on the diffuse interface phase-field approach, which may also be applied in its general form to a wide variety of phase separating and supercritical systems. For processes occurring over very small length scales, e.g. nucleation and growth, such computations though resulting in finite thickness interfaces do capture the necessary physical phenomena. For larger length-scale multiphase structures, the interface becomes a contact discontinuity, and the method smoothly transitions into a level-set-like formulation. However, in this second form the sharp interface is computationally difficult to handle. A second method for such problems based on a variation of the ghost-fluid method, in which sharp interfaces can be captured, will be presented. Applications will be shown at the two extremes of scales, including early stages of nucleation, growth and coarsening of multiphase structures, as well as macroscopic flows in which length-scales and velocities are large.