Improving the Scaling of Two-Phase Damping by Local Observations in a Tube Bundle

Abstract

Experimental data are reported to investigate the dissipation mechanisms that govern two-phase damping and fluid-elastic instability of a single flexible tube in a rigid array. The working fluid is an air-water mixture and the void fraction and interfacial velocity are measured using a bi-optical probe (BOP) positioned upstream of the flexible tube. The present work aims at revisiting the problem of fluid-elastic instability by developping various scaling models of two-phase fluid damping before the onset of instability. For most of the experiments, the measured damping factor was seen to increase with increasing bubble chord length, with decreasing superficial liquid velocity, and with decreasing amplitude of vibration. The Connor’s approach has been generalized to the two-phase flows provided that the reduced velocity is calculated with gas velocity and with mixture density deduced from the local void fraction measured inside the bundle. The collapse of the fluid-elastic data is more satisfactory than when using the Homogeneous Equilibrium Model (HEM). Void fraction, gas velocity, relative velocity, liquid superficial velocity, bubble chord length, vibratory frequency are shown to be relevant parameters to reduce the two-phase damping data. The use of these parameters in non-dimensional numbers such as Capillary number, Reynolds number, pressure ratio, mass ratio leads to helpful observations as well as several promising approaches to the reduction of two-phase damping.