Control of Fluid Forces Acting on a Circular Cylinder and Its Effectiveness : Controlled by a Fine Circular Cylinder

Abstract

The objective of this paper is to investigate the suppression of the fluid forces acting on a circular cylinder (called test cylinder) by controlling the flow around it. The control of the flow was established by introducing a fine circular cylinder (called control cylinder) in the neighbourhood of the test cylinder. Measurements were carried out by varying the position of the control cylinder in the ranges of G=0.2∼10mm (G is gap between two cylinders) and α=0°∼180° (α is angle along the circumference of the test cylinder). Then, the steady and unsteady fluid forces, vortex shedding frequency and flow pattern were systematically examined. Furthermore, such matters as the mechanism of control, the controlled wake structure and the relation between the characteristics of the controlled fluid forces and the behaviour of the flow were discussed in detail based on the results of the fluid forces, vortex shedding frequency and flow pattarn. In particular, it was found that the maximum reduction of the time-mean drag was 50%, and the maximum reduction in the fluctuating lift and drag was 85% by using the control cylinder with the diameter of 3mm, which is considerably small compared to the test cylinder with that of 49mm.