Self-excited vibration of cross-shaped tube bundle in cross-flow

Abstract

A cross-shaped tube bundle is proposed for the lower plenum structure in next-generation LWRs. The vibration response of the cross-shaped tube bundle in cross-flow has been measured in water tunnel tests. First, a small-scale test was conducted. Tests were conducted with 3×3 flexible tubes as well as a single flexible tube in a rigid tube bundle. The flexible tubes could vibrate in the lift, drag, and torsional directions. The effect of the arrangement of the tube bundle and the natural frequency ratio of translational and torsional vibrations were considered. Second, a large-scale test was conducted for only one case to check the effect of Reynolds number, in which the Reynolds number was 10 times larger than that of the small-scale test. In all the cases, large-amplitude vibration appeared when the flow velocity became larger than a critical value, and self-excited vibration was found to occur. The nondimensional critical gap velocity of the large-scale test agreed well with that of the small-scale test, which suggested that the effect of Reynolds number was not so large. A design guideline to prevent self-excited vibration is proposed for the cross-shaped tube bundle.