Study on the Vibrational Characteristics of a Tube Array Caused by Two-Phase Flow. Part II: Fluidelastic Vibration

Abstract

Fluidelastic vibration of tube arrays caused by two-phase flow has been studied before. The critical flow velocity is usually estimated with a simple Connors-type criterion which is based on an average flow velocity, an average fluid mass density and damping in two-phase flow. However, there is no explanation of why this simple criterion is applicable or how fluidelastic instability occurs in two-phase flow. This paper presents experimental results on the fluidelastic vibration caused by air-water flow and by steam-water two-phase flow in condition of up to 7·0 MPa pressure and temperature reaching 284°C. A new criterion, based on an assumption of energy balance per cycle of oscillation, is introduced using the "true" flow velocity. However, comparison with the experimental data indicates that, in the slug or froth flow regimes, the speed of the intermittently rising slugs, introduced in Part I of this study, should be used; hence, a new modified criterion for the slug and froth flow regimes is derived. In addition, the new criterion is compared with the usual Connors-type criterion which greatly depends on the estimation of the damping in two-phase flow. The agreement between the two criteria is found to be within the uncertainty introduced by the variance in the unknown parameters in the Connors criterion.