Numerical simulations of flow around two circular cylinders in cruciform arrangement and two spheres in tandem arrangement by virtual boundary method

The virtual boundary method was applied to simulate the flow passing around two circular cylinders in cruciform arrangement at Re=150. Spatial structures of the flow wake are different at various spacing ratio. When the spacing ratio is greater than 3, for upstream cylinder, the influence of downstream cylinder is restricted in the region that the wake of downstream cylinder coexists, and out of this region the wake of upstream cylinder maintains a regular Karman vortex street. When the spacing ratio is smaller than or equal to 3, for upstream cylinder, the influence of downstream cylinder is expanded to the whole spanwise of the upstream cylinder wake, and obvious three-dimensional structures can be observed. In the case that spacing ratio smaller than or equal to 3, in the plane in near wake of downstream cylinder, four symmetrical vortices come into being. Other detailed parts of the flow field are addressed in this paper, and some macro-variables such as vortex shedding frequency, lift and drag coefficients are also calculated in this paper.