On the Mechanism of Fluidelastic Instability of a Tube Placed in an Array Subjected to Two-Phase Crossflow

Abstract

In this work, the fluidelastic instability of a tube placed in an array subjected to two-phase crossflow has been studied. For the determination of fluidelastic instability, acrylic tubes 2.2 cm or 2.37 cm in diameter and 20 cm in length were arranged in a triangular array with pitch to diameter ratio of 1.4 and 1.3. The test tube was flexibly supported with two cantilever beams. By installing cantilever beams horizontally and vertically, drag and lift direction tube vibration were studied. The total damping ratio is found to increase as the liquid gap velocity or void fraction increases. It has been found that the effective spring constant decreases rapidly with increase of liquid gap velocity or void fraction just prior to the onset of instability. For the range of parameters studied in this work, the onset of fluidelastic instability is associated with a rapid decrease of the effective spring constant because for a given applied force the amplitude of the tube vibration is inversely proportional to the spring constant.