Fluidelastic instability tests on an array of tubes preferentially flexible in the flow direction

The present work is motivated by the observation that, in the presence of flat bar supports (AVBs), U-tubes in steam generators and heat exchangers may not be restrained in the in-plane direction. The stability behavior of a rotated triangular array is investigated in detail in the present work. Tests are conducted with a fully flexible array, a single flexible tube, and a finite number of flexible tubes at several locations within the otherwise rigid array. In all cases tube flexibility is purely in the flow direction. The fully flexible array is shown to undergo fluidelastic instability. Despite the unidirectional flexibility constraint, the critical instability velocity is of the same order of magnitude when compared with previous tests on an unconstrained fully flexible array. A single flexible tube, on the other hand, is found to be stable. Results of tests on partially flexible array configurations are also presented.