Research on flow around two tandem rectangular cylinders

Uniform flow around two identical rectangular cylinders arranged in tandem has been investigated via the lattice Boltzmann method. With a fixed Reynolds number of 100, the effects of side ratio (gamma = 1/2, 1/4, 1/8 and 1/16) and spacing ratio (S* = 0.25-12) on the fluid dynamics are investigated. Results indicate that both side ratio and spacing ratio have significant influences on the flow structure, vortex shedding frequency and hydrodynamic force. Several distinct vortex wake modes including the single bluff-body (SBB), shear-layer reattachment (SLR) and secondary vortex formation (SVF) modes are observed. The variations of Strouhal number, drag and lift coefficients versus spacing ratio are similar between all the current side ratios. In the branches of small and large spacing ratios, the fluid dynamics are obviously different and there is a critical spacing ratio, beyond which the relevant mechanical parameters jump suddenly as a result of the flow mode transition. A phenomenon of two -stage drag frequency separation between two cylinders occurs in the region of low side ratio and large spacing ratio, and its formation mechanism has also been analysed on the basis of flow characteristics and frequency spectra of force coefficients.