Enhancing hydrodynamic drag and lift reduction around two staggered obstacles via control plates

Abstract

This study analyzes the enhancement of hydrodynamic forces reduction for flow around two identical square cylinders arranged in a staggered manner utilizing the control plates. Effects of attached flat plates on flow structures and fluid forces acting on cylinders are examined by considering plates length (l) = 0.1–10 times cylinder’s size. The gap distance between cylinders (g) is fixed at 2.5 times cylinders' size with a fixed Reynolds number of 200. Four different flow patterns revealed in this study: synchronized flow pattern for l = 0.1 to 0.6, quasi flip-flopping flow pattern for l = 0.7 to 1.9, modulated synchronized flow pattern for l = 2 to 4.1 and quasi-periodic flow pattern for l = 4.2 to 10 while non-synchronized flow pattern is observed for staggered cylinders without plates at g = 2.5. The flow patterns variation is found to be directly linked with variations in Strouhal number (St) of both cylinders. The fluid force parameters decreased significantly with increasing length of plates as compared to two staggered cylinders without plates. In particular, mean drag coefficient (CDmean) reduces maximum up to 91% at l = 0.8, root-mean-square value of drag coefficient (CDrms) reduces up to 82% at l = 0.1, root-mean-square value of lift coefficient (CLrms) reduces up to 94% at l = 0.3, St reduces up to 72% at l = 10, the amplitude of drag coefficient (CDamp) reduces up to 78% at l = 0.8 and amplitude of lift coefficient (CLamp) reduces up to 87% at l = 0.2. The plates are found more effective in controlling the flow around the second cylinder as compared to the first cylinder. This study also reveals that at some plate lengths, instead of reduction, an increase in hydrodynamic force values occurred compared to the uncontrolled case.