摘要
A Cartesian grid-based, immersed-boundary method combined with a moving domain is used to simulate sphere and oblate spheroid settling under gravity. For the moving domain, grids are generated or deleted based on the location of the object centroid, ensuring a constant size of the computational mesh. Sphere settling under gravity is first simulated, and the predicted drag coefficients at different Reynolds numbers, that is, 4.1 to 2000, agree reasonably with measurements. Finally, an oblate spheroid descending under gravity is further simulated with Reynolds numbers at 44.5 to 1617. For the Reynolds numbers examined, the motions are two-dimensional, and the fluttering motions exist in all the Reynolds numbers investigated except at Re = 44.5, in which steady falling prevails. This is consistent with previous investigations for falling disks, where the threshold for the steady and fluttering motion is at around Re = 80 for the level of moment of inertia investigated. As the spheroid flutters, different vortex branches are generated in the trailing edge direction, in which hairpin-like vortices occur.