Vortex structure manipulation and drag reduction of tandem circular cylinders using a pitching splitter plate

In this article, two-dimensional numerical simulations are performed to investigate the effectiveness of a hinged splitter plate for manipulating the unsteady laminar wake regime of tandem circular cylinders (TCCs) at a pitch ratio of G/D = 5 and Reynolds number of Re = UD/υ = 100, where G is the distance between the centers of the cylinders having diameter D, U is the free-stream velocity, and υ is the kinematic viscosity of the fluid. These simulations are conducted using the in-house developed flexible forcing immersed boundary-one-step simplified lattice Boltzmann method (FFIB-OSLBM) solver. The splitter plate is hinged to the upstream cylinder's rear base point (HSPU) that pitches at amplitudes θm (10°–20°) and non-dimensional frequencies Stf (0.1–0.4). The plate length Lf/D is varied between 0 and 1. These pitching parameters substantially influence the wake topologies, vortex-interaction modes, pressure distribution, and flow-induced forces on the cylinders. Moreover, the TCC-HSPU combination exhibits four different wake patterns. In Type-I, regular vortex shedding occurs, with the upstream cylinder vortex (UCV) dominating the plate vortex (PV) in the cylinder gap region. The stronger and bigger PV in Type-II forms parallel vortex streets. In Type-III, the PV becomes strong enough to prevent the shedding of UCV. Finally, in Type-IV, the PV attains its maximum strength, and its interaction with UCV forms a new vortex that dominates the cylinder gap region. Among them, Type-II and Type-III regimes are associated with a lower range of drag force on TCC-HSPU configurations. In the considered parametric space, the TCC-HSPU arrangement achieves a maximum drag reduction of 43% compared to the TCC when Lf/D = 1.00, Stf = 0.20, and θm = 15°.