Reduction of hydrodynamic forces on circular and square cylinders by a rear-attached splitter plate

This study investigates the influence of a rear-attached splitter plate on the flow and hydrodynamic characteristics of circular and square cylinders. Two-dimensional direct numerical simulations are performed over broad parameter spaces of Reynolds number (Re) and non-dimensional plate length (L/D, where L represents plate length and D denotes diameter for a circular cylinder or side length for a square cylinder), including (Re, L/D) = (10–400, 0–6) for a circular cylinder and (Re, L/D) = (10–240, 0–6) for a square cylinder. In general, the mean drag coefficient, root mean square lift coefficient, and Strouhal number decrease with increasing L/D in a nonlinear manner. For the same increment in L/D, the force reduction for L/D ≤ 1 is much stronger than that for L/D ≥ 2. Specifically, as L/D increases from 1 to 2, the streamwise location of vortex formation moves from downstream of the splitter plate to the two sides of the plate (for Re ≳ 200), which results in a local increase in the hydrodynamic force coefficients. This finding explains why an optimal control at L/D ∼ 1 was often observed in various bluff-body flows. A comparison between circular and square cylinder scenarios indicates that the splitter plate is more effective for a circular cylinder in terms of force reduction. This is because the separation location on a circular cylinder can adjust to changes in the flow field, such that the splitter plate is able to change the flow field to a greater extent.