Passive control on flow structure around a wall-mounted low aspect ratio circular cylinder by using an inclined hole

Abstract

To control and reduce the rear separation region and the vortex of the free-end surface, a passive flow control method that is to use an inclined flow controlling hole (FCH) passing through the free-end surface to the side of the rear surface was proposed for a low aspect ratio (=1) circular cylinder. The high-speed PIV (Particle Image Velocimetry) measurements were performed at Reynolds number of 8,570 in a circulation water tunnel in order to compare the flow characteristics between the controlling and no-controlling wakes. Furthermore, to study the position effect of the FCH, there kinds of the FCH models were tested. It was found that the fluid flows from the large rear recirculation zone upwards to the small recirculation zone on the free end surface through the FCH. The size of rear recirculation zone was reduced by the FCH cylinders with h = 50 mm, and the FCH cylinders with h = 20 and 35 mm effectively diminished the separation region of the free end surface. Meanwhile, vorticity, Reynolds shear stresses and turbulent kinetic energy were also decreased by the FCH cylinders with h = 50 mm comparing with the standard cylinder and other FCH models. Spectral analyses suggest that the dominate frequency of vortex shedding from the cylinder surface increases.

Keywords

• flow controlling hole
• passive control
• piv
• low aspect ratio cylinder
• vortex
• wake
• wavelet transform