Simulation of flow across two tandem cylinders with different diameter by discrete vortex method

A discrete vortex model has been developed to solve the unsteady vortex dynamics equation under the Lagrangian frame, in which the point vortex was used to represent the location where vorticity concentrated. The transient evolution of vortex shedding process behind two tandem cylinders with different diameters was simulated effectively and the influence of large-scale coherent structure in the flow field on the two cylinders was analyzed. It is found that small vortices will be entrained by the large-scale coherent structure to form larger vortices with higher vorticity. When the front cylinder is big and the rear one is small, there is little change on the drag and lift coefficients of the big cylinder compared with the case of single cylinder. The drag coefficient amplitude of the big cylinder will nearly keep constant. The drag coefficient amplitude of the small one will increase while the average value will be close to zero. The lift coefficient amplitude of the big one will increase and the average value of both cylinders will be close to zero. When the front cylinder is small and the rear one is big, the amplitude of drag coefficient of the big one will increase and the average value will decrease while the amplitude of the small one will decrease and the average value will increase. The lift coefficients of the two cylinders tend to be the same with each other and the average values are close to zero.