Three-Dimensional Fragmentation of Core-Annular Flow Haoxiang Luo, Department of Mechanical Engineering Vanderbilt University, Nashville, TN 37235 Objective: in this project we are going to develop an efficient 3D computational approach to model the break-up and coalescence of interfaces encountered in two-phase flows. In addition, the approach will be able to handle complex/moving solid geometries. The approach will be applied in the core-annular flow to study the interfacial fragmentation. To do this, we combined two types of immersed-boundary (IB) method, one for the fluid-fluid interface using a “diffuse” representation of the surface, and one for the fluid-solid interface using a “sharp” representation. The overall method employs a single-block, fixed, and structured mesh. The diffuse-interface IB method (Peskin, 2002) where interfacial discontinuities are regularized. The sharp-interface IB method (Mittal et al, 2008; Luo et al, 2010) where the combined finite-difference discretization and flow reconstruction are used near the boundary. A code demo showing a droplet going through an irregular channel.