Dynamics of an inline tube array in steam-water flow. Part 1: Damping and added mass

Fluidelastic instability remains an important problem in operating steam generators. In a recent MHI study three important aspects of the problem were considered, (i) two-phase fluid damping and added mass under prototypical conditions, (ii) the nature of unsteady fluid forces leading to fluidelastic instability and finally (iii) the fluidelastic instability mechanism itself. This paper is the first in a three part series reporting on the findings of this study. Two-phase fluid damping is directly attributable to the coexistence of multiple fluid phases. It is dominant at low flow velocity and, hence, must be considered in any stability analysis. Experimental tests have been conducted to determine two-phase flow damping under prototypical high temperature and pressure conditions, up to 5.8 MPa at 273 C. The test array was of an inline geometry. Two separate arrays were tested. The tests showed that there is a distinct difference between drag and lift direction damping. Tube added mass showed a quasi-linear vibration with void fraction. Added mass values were found to vary significantly from computed values assuming homogeneous fluid properties. Damping and added mass are needed to deduce the flow dependent damping and stiffness components of the unsteady fluid forces presented in Part 2 ofmore » this series. The measured damping and added mass data are also vital in stability analysis which is the subject of Part 3 of the series.« less