The experimental investigation on wake dynamics of flow around a circular cylinder with the splitter plate

The wake dynamics of flow around a circular cylinder with the splitter plate are investigated using particle image velocimetry (PIV). The Reynolds number based on the cylinder diameter $D$ is $Re=3.9\times {10}^3$, and the ratio of the splitter plate length $L$ on the cylinder diameter varies from $L/D=0$ to $L/D=2.5$. The wake characteristics and vortex dynamics are strongly dependent on $L/D$. There are main and secondary recirculation regions behind the cylinder, and the range of the recirculation region presents an obvious increase as $L/D$ increases from 0 to 1 due to the elongations of the cylinder shear layers. Moreover, the maximum velocity defect and the wake width are increased with increasing $L/D$, and the short splitter plate has important influences on the wake characteristics for $L/D\le 1$. Based on the vortex dynamics, the splitter plate length can be divided into three regions. (i) For $0\le L/D<1$, the shear layers elongate downstream further to form Karman vortex sheets as $L/D$ increases, and the wake vortices induce formation of the secondary vortex on the trailing edge of the plate. (ii) For $1\le L/D<2$, the secondary vortex moves upstream along the plate and gradually lifts up, and the wake vortices are easily broken into some small-scale vortices due to the disturbance of the plate. (iii) For $L/D\ge 2$, the wake vortices are reattached on the plate, and the secondary vortex is mainly distributed behind the cylinder. The Strouhal number $St$ decreases nearly by 26.34 % from $St=0.205$ at $L/D=0$ to $St=0.151$ at $L/D=1$, and $St$ presents an increase as $L/D$ increases from 1 to 2. The magnitudes of Reynolds stresses and turbulent kinetic energy are decreased with increasing $L/D$, and the splitter plate significantly inhibits the production of Reynolds vertical normal stresses, which makes a significant contribution to inhibit wake fluctuations of the cylinder.