Fluid-particle simulations reaching 100 particles

We have developed a new high performance computing tool for 3D simulation of fluid-particle interactions with the number of particles reaching 100. The mathematical modeling is based on the time-dependent Navier-Stokes equations governing the flow around the particles and Newton's law of motion governing the 3D dynamics of the particles. This tool is based on a stabilized space-time finite element formulation for moving boundaries and interfaces and implementation of this formulation on parallel platforms. The other methods developed for this purpose include: fast automatic mesh generation with structured layers of elements around particles, a mesh update method based on automatic mesh moving with remeshing only as needed, an efficient method for projecting the solution after each remesh, surface mesh refinement to increase accuracy when two solid surfaces get close, and multi-platform computing with high-speed interplatform communication. In these simulations, while the mesh partitioning, flow computations, and mesh movements are performed on a 512-node CM-5, the mesh generation and projection is accomplished on a 20-processor SGI Onyx system. The two platforms communicate via a HiPPI channel. To test and demonstrate this new capability, we applied it to the simulation of 101 spheres falling in a liquid-filled tube. The spheres, in addition to interacting with the fluid, interact and sometimes collide with each other and with the tube wall. We simulated two cases with 101 spheres: with the size of the spheres random in one case and uniform in the second. In both cases, the simulation is started with the spheres distributed randomly in the tube. Several spheres exhibit drafting, touching and tumbling in both cases. The approximate, average Reynolds number is 40 for both cases.