Study on flow past two spheres in tandem arrangement using a local mesh refinement virtual boundary method

Abstract

SUMMARYA local mesh reÿnement virtual boundary method based on a uniform grid is designed to study the transition between the ow patterns of two spheres in tandem arrangement for Re = 250. For a small gap (L=D = 1:5), the ow ÿeld is axisymmetric. As the spacing ratio increases to 2.0, the pressure gradient induces the circumferential uid motion and a plane-symmetric ow is constructed through a regular bifurcation. For L=D ¿ 2:5, the vortices are periodically shed from the right sphere, but the planar symmetry remains. The case for L=D = 3:0 is picked up to give a detail investigation for the unsteady ow. The shedding frequency of vortical structure from the upper side of the right sphere is found to be double of the frequency of the lower side. With the ow spectra of various gaps given, the underlying competitive mechanism between the two shedding frequencies is studied and a critical spacing gap is revealed.

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