Splitter plate-based flow control study for two square cylinders in tandem arrangement

Abstract

A numerical study is performed to investigate the effectiveness of a splitter plate (SP) for the unsteady wake-regime control of two-dimensional tandem square cylinders (TSC) arranged with large (G/D = 6), intermediate (G/D = 4) and small (G/D = 2) gap-widths. Here, G is the center-to-center distance between the cylinders, and D is their side-length. The numerical simulations are conducted using an in-house developed FFIBLBM (flexible-forcing-immersed-boundary-lattice-Boltzmann-method) solver at Reynolds number (Re) of 100. The TSC arrangement with SP attached to either upstream or downstream cylinders is named TSC-SPU and TSC-SPD, respectively. It is found that the shear-layer characteristics, wake-regime, and flow-induced forces on TSC are highly susceptible to the G/D ratio and SP length. We observed four distinct flow patterns: VS-VS (vortex shedding-vortex shedding), QS-VS (quasi-steady-vortex shedding), S-VS (steady-vortex shedding), and S–S (steady-steady) in the wakes of TSC. Among them, the S–S flow pattern is the controlled wake-regime, with steady and stabilized vortices behind both cylinders, yielding considerably lesser drag on the TSC. Precisely, at large gap-width (G/D = 6), the TSC-SPU configuration only attains the S–S flow type for which the upstream and downstream cylinder experience 11.86% and 97.73% lesser drag, respectively, than the TSC without an attached SP. However, at intermediate gap-width (G/D = 4), both TSC-SPU and TSC-SPD generate the S–S flow type. Still, the TSC-SPU is advantageous in drag reduction, where the drag of the upstream and downstream cylinders is reduced by 1.61% and 7.26%, respectively. On the other hand, the S–S flow type is established for low gap-width (G/D = 2) with TSC-SPD setup for which the drag reduction for upstream and downstream cylinders are 1.85% and 12.76%, respectively.