Numerical investigation of the flow around two circular cylinders in tandem

The incompressible flow around pairs of circular cylinders in tandem arrangements is investigated in this paper. The spectral element method is employed to carry out two- and three-dimensional simulations of the flow. The centre-to-centre distance (lcclcc) of the investigated configurations varies from 1.5 to 8 diameters (D  ), and results thus obtained are compared to the isolated cylinder case. The simulations are in the Reynolds number (Re) range from 160 to 320, covering the transition in the wake. Our analysis focuses on the small-scale instabilities of vortex shedding, which occurs in the Re range investigated. With the aid of Strouhal data and vorticity contours, we propose mechanisms to explain the interference phenomenon and its interaction with the three-dimensional vortical structures present in the flow field. It is found that, for Re>190Re>190, when three-dimensional structures are present in the flow field, two-dimensional simulations are not sufficient to predict the (Re,lcc)(Re,lcc) pair of drag inversion.