Euler-Lagrange scheme for modeling particle-laden flows in medical image-based geometries

We describe the implementation of a coupled computational fluid dynamics - discrete element method (CFD-DEM) approach for modeling particle-laden biological flows in patient-specific geometries. There have been significant advances in the Euler-Lagrange modeling paradigm in recent years, but this has been largely restricted to studying engineering problems on structured grids. Here, we extend the CRIMSON cardiovascular flow framework to model Lagrangian particles that interact with each other and are coupled with the fluid. The incompressible Navier-Stokes equations are solved using a stabilized finite-element method on an unstructured grid. Rigid particle collisions are modeled using a damped soft-sphere approach. We employ an efficient hash-table based cell-list to accelerate particle collision detection in complex domains. Particle-fluid coupling is performed using a two-stage procedure that decouples the particle sizes from the mesh element size. The resulting process is a consistent, conservative and convergent method that naturally handles complex geometries. These improvements contrast with prior approaches on unstructured grids. The method developed here is used to study benign paroxysmal positional vertigo which is caused by particles settling in the semi-circular canals of the inner ear.