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Experimental investigation of in-flow fluidelastic instability for square tube bundles subjected to single-phase and two-phase transverse flows
Xavier Delaune, Philippe Piteau, Laurent Borsoi, Jose Antunes

Last modified: 2018-04-19


In-flow fluidelastic instability of tube bundles has been the subject of a strong renewed interest, since the unanticipated failure of the replacement steam generators of the San Onofre nuclear power station in 2012. A literature review on the topic discloses contrasting views, which may be condensed as follows: (1) For square bundles, in-flow fluidelastic instability was never observed under single-phase flows, while for two-phase flows experimental data is virtually nonexistent. (2) For triangular bundles, in-flow fluidelastic instability has been observed under single-phase flows, the stability boundary being dependent on the number of flexible tubes, while for two-phase flows in-flow instability does not seem to depend consistently on the bundle flexibility configuration. For a single flexible tube within a rigid bundle, no in-flow instability has been observed, whatever the nature of the flow. On the other hand, for both single-phase and two-phase flows, the in-flow instability boundary is always delayed with respect to the cross-flow instability boundary.

By far, French nuclear power stations are mostly equipped with steam generators designed using square bundles. This paper presents the results of an extensive experimental investigation on the in-flow stability features of square bundles, performed at CEA-Saclay. A 5x3 square bundle with P/D=1.5 and D=30mm was subjected to single-phase and two-phase air-water (with void fractions 80%, 90% and 98%) transverse flows, for four different flexibility configurations. In all cases, the flexible tubes were mounted using anisotropic supports, only allowing for in-flow vibratory motions. To our best knowledge, this is the first time that in-flow test results are obtained on square bundles subjected to two-phase flows.

The following conclusions stem from the experimental results obtained: (a) For both single and two-phase flows, and for all tested flexibility configurations, no instability was observed in the tests performed; (b) These results support those obtained by Nakamura et al. (2015) and Cardolaccia & Baj (2015), for similar tested configurations; and (c) They highlight the essential contrasting behavior of triangular and square bundles, when addressing in-flow fluidelastic instability.


in-flow fluidelastic instability, square tube bundle, two-phase flow

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