Flow-Induced In-line Oscillation of a Cantilevered Tapered Circular Cylinder

Abstract

The flow-induced in-line oscillation of a tapered circular cylinder which was supported by a plate spring was experimentally studied through free-oscillation tests in a water tunnel. The response displacement amplitude at a cylinder tip was measured at roduced velocity Vr from 1.0 to 4.0. The taper ratio was varied from 0% to 20% to investigate its effect on the response displacement. The tip diameter of each cylinder was 20 mm and the root diameter was varied. It was found that cylinders with taper ratios of 2.5% to 10% had two excitation regions, while cylinders with taper ratios less than 1% had one excitation region. The taper ratio, therefore, affects the amplitude of the second excitation region. The reference diameter of the tapered cylinder was defined by the diameter at 1/3 length from tip in consideration of the results of oscillation characteristics of tested cylinders. The cylinder with any taper ratio did not oscillated at Vr <1.0. The amplitude of the cylinder with any taper ratio was suppressed at less mass-damping parameter Cn than 2.5, which is the suppression criteria for in-line oscillation of 2-dimensional cylinder. The guideline JEME S 012 of the Japan Society of Mechanical Engineers is valid for tapered circular cylinders, since it is established in consideration of 2-dimensional cylinder.