Flow-Induced Vibrations of a Circular Cylinder Interacting with Another of Different Diameter

Abstract

The work investigates flow-induced response of a circular cylinder interacting with another smaller diameter cylinder placed upstream. The upstream cylinder diameter d was varied from 0.24 to 1.00 times the diameter D of the downstream cylinder, which was cantilever-supported. Experimental observation was made at a spacing ratio, L/d, of 1–2, where L is the center of the upstream cylinder to the forward stagnation point of the downstream. A violent vibration of the cylinder occurred at d/D = 0.24–0.8 for L/d = 1 or d/D = 0.24–0.6 for L/d = 2, but not at d/D = 1. The violent vibration occurs at a reduced velocity U _r  = 13–22.5, depending on d/D and L/d, and increases rapidly, along with the fluctuating lift, for a higher U _r . At a small d/D, the upstream cylinder wake narrows, hence the high-speed slice of the shear layer could flow alternately along the two different sides of this cylinder, thus exciting the downstream cylinder.