Fluid forces acting on a circuler cylinder immersed in a sinusoidally oscillating flow at a low keulegan-carpenter number

It is the purpose of this paper to make clear the cause for the considerable dispersion of inertia and drag coefficients of a circuler cylinder in a sinusoidally oscillating flow at low values of Keulegan-Carpenter's number. Drag and lift forces are measured by cantilever beam system with four PN semi-conductor gages simultaneously. The flow around a circuler cylinder are visualised by electrolysis. The following properties became evident after examining the experimental results. In the case of the process from production to shedding of eddy is symmetric with respect to a line of mainflow passes through a cylinder axis, the drag and resultant force coefficients shows a value about 2 times as mach of asymmetric formation of eddy at same K-C number. Asymmetric formation of eddy plays an important role to change the direction and magnitude of approaching velocity. As a result of these, it induce strong lift and decrease of drag and resultant forces.