Flow-Induced Vibration of Two Square Cylinders With Rounded Corners in a Tandem Arrangement

Abstract

Based on the design of the heat transfer tube bundles with square cross section of the steam generators in high temperature reactor-pebble bed modules (HTR-PM), a free-vibration experiment is conducted to examine flow-induced vibration (FIV) characteristic of two identical rounded square cylinders with r/D = 0.12 in tandem arrangements at spacing ratio L/D = 1.5∼5.5. One of the cylinders is two-dimensional, spring mounted, and allowed to vibrate in the cross-flow direction while the other is held stationary. Considering two cases that elastic cylinder located upstream or downstream, two mass-damping ratios m*ζ are chosen to investigate the effect of spacing between two cylinder. The vibration responses and the flow structure around two cylinders are studied, using laser displacement sensor and Particle image velocimetry. It is observed that only vortex-induced vibration (VIV) occurs when the elastic cylinder is located downstream. When elastic cylinder is located upstream, the full interaction between VIV and galloping of cylinder with lower m*ζ is invariable no matter what the spacing is. The spacing has noticeable effects on the vibration behavior of cylinder with higher m*ζ and changes the interaction between VIV and galloping. The flow structure of two cylinders indicates that the upstream shear layer reattaches on the surface of the downstream cylinder as L/D < 3.5, where the St drops with increasing L/D. There is gap vortices between two cylinders at L/D > 3.5 where the St rises and is close to the value of single cylinder with a larger spacing.