Effect of a horizontal hole on flow structures around a wall-mounted low-aspect-ratio cylinder

• Published in: The International journal of heat and fluid flow 2018-06, Vol.71, p.80-94
• Main Authors: Rinoshika, Hiroka, Rinoshika, Akira
• Format: Article
• Language: English
• Subjects: Flow controlling hole; Flow separation region; Low aspect ratio cylinder; Passive flow control; PIV; Vortex; Wake
• ISSN: 0142-727X; 1879-2278
• DOI: 10.1016/j.ijheatfluidflow.2018.03.003

•A passive flow control method using a horizontal controlling hole is proposed.•The rear separation region was reduced by the HCH cylinder.•The vorticity strength is decreased by the jet flow.•Reynolds shear stresses and turbulent kinetic energy were suppressed.•The large-scale vortex was broken down into several small-scale vortices. To control the vortex structures and separation region of a low-aspect-ratio cylinder wake, a passive flow control method that is to drill a horizontal hole from the front side surface to the rear side surface was proposed for a short circular cylinder having an aspect ratio H/D = 1 with height H and diameter D of 70 mm. The PIV measurements were performed at Reynolds number of 8570 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 horizontal hole, three kinds of the hole positions having different height h from wall were tested. It was found that the jet flow from a horizontal hole leads to suppress the vortex formation and to reduce the rear separation region. The vorticity, Reynolds shear stresses and TKE were evidently suppressed by the jet flow of the horizontal hole in the rear recirculation zone, resulting in the reduction of the drag acted on the cylinder. Meanwhile, the instantaneous large-scale vortical structures of the rear recirculation zone were broken down into several small-scale vortices by the jet. As increasing the height of hole, the downwash flow is evidently suppressed and the upwash flow is increased. Spanwise vortex shedding is altered from symmetric to asymmetric arrangement.