Zhaosheng Yu
PhD thesis title:
Numerical Simulation of Particulate Flows with Fictious Domain Method
Objective:
The distributed Lagrange multiplier/fictious domain method(DLM) is a promising method for the direct numerical simulation of particulate flows due to its two features: first, the fluid-flow problem is posed inside,as well as outside, the particle boundaries,as a result, a fixed structured grid can be used for the entire simulation, eliminating the need for repeated remeshing and projection; second,the fluid-particle motion is treated implicitly via a combined weak formulation in which the mutual forces cancel and explicit calculation of the hydrodynamic forces and torques on particles is not required. We have devised a simpler and more accurate implementation of the DLM method compared to the previous DLM codes. The paralellization of the three-dimensional DLM code is under way.
Background:
Direct numerical simulation of particulate flows is a way of determining the motion of particles in fluids exactly,without any approximation in the sense that the Navier-Stokes equations governing the motion of the fluids and the equations of rigid-body motion governing the motion of the particles, coupled by the no-slip condition on the particle boundaries and the hydrodynamic interactions, are solved simultaneously. The direct numerical method can take into account all non-linear effects caused by the particles. Those approximate methods based on potential flow, Stokes flow,and point-particle approximations, however,simplify the computation by ignoring some possibly important effects like viscosity and wakes in the case of potential flow, inertial forces which produce lateral migration and across-the-stream orientations in the case of Stokes flow,and the effects of stagnation and separation points in the case of point-particle approximations. The direct numerical method is well-suited to investigation of microstructure in flowing suspensions of particles and some industrial problems like sedimentation columns, fluidized beds,slurry transport and hydraulic fracturing.
Vorticity contours for a circular particle settling in a channel showing periodic vortex shedding and formation of the Karman vortex sheet.
