Vibration Mechanism of Two Inline Cylinders

Abstract

The paper presents an experimental investigation on flow-induced vibrations of two circular cylinders in tandem arrangement for spacing ratio L/D = 1.2–6.0 and reduced velocity U_r = 3.8–47.8, where L is the cylinder center-to-center spacing and D is the cylinder diameter. Both cylinders are allowed to vibrate in the cross-flow direction only. Extensive measurements are conducted to capture the cylinder vibration responses, surface pressures and flow fields using laser vibrometer, pressure scanner and PIV techniques. Four vibration regimes are identified based on the vibration characteristics and generation mechanism of the galloping vibration generated for the cylinders. Then the insight into the vibration generation in each regime is explored through an examination of the gap shear layer behaviour, vortex shedding process and pressure distribution around the cylinders. The gap vortices around the base surface of the upstream cylinder lead to the large vibration of the upstream cylinder. On the other hand, the gap shear layer interacts with the downstream cylinder which causes the change in the pressure distribution over the front and side surfaces, leading to the large vibration of the downstream cylinder.