Simulations of particle dispersion around multiple circular cylinders via an immersed boundary method

Abstract

A modified immersed boundary method is extended to study fine particle dispersion in particle-laden wake flows around multiple stationary circular cylinders, with a Reynolds number of 250. The fixed Cartesian grid is applied and the no-slip condition near the surface of circular cylinders is satisfied through a direct forcing technique. The governing equations for fluid flow are directly solved using high-order finite difference schemes and the dispersed fine particles are tracked in the Lagrangian framework based on point-source assumption. The numerical algorithms are first validated by simulating flows around a single circular cylinder. For flows around two side-by-side circular cylinders, three typical flow regimes are observed for different gap ratios. For flow around three staggered circular cylinders, the coherent structures first appear in symmetrical mode with large recirculation zones, but then change to asymmetrical mode and finally develop into a complex single vortex street. The particle dispersion is found to be closely related to the number of the circular cylinder and the gap ratio, in addition to the particle Stokes number. For various numbers of circular cylinder and gap ratios, the flow displays different coherent structures, resulting in different particle distributions. But for a fixed number of circular cylinder and gap ratio, the particle Stokes number becomes the controlling parameter.