THE POST-HOPF-BIFURCATION RESPONSE OF A LOOSELY SUPPORTED CYLINDER INAN ARRAY SUBJECTED TO CROSS-FLOW .1. EXPERIMENTAL RESULTS

The dynamic response of a loosely supported cylinder, unstable in its first TSP-inactive mode (i.e., when no support is provided by the Tube Support Plate), is investigated experimentally. The test cylinder, mo delled by a flexibily mounted rigid tube, was part of an array of rigi d cylinders in a rotated triangular array with pitch-to-diameter ratio 1:375 subjected to water cross-flow. Tests were conducted with the fl ow velocity as the main variable parameter. The effect of other parame ters, including cylinder-support gap size, support material properties and the interstitial fluid in the impact zone, was also explored. Dis tinct bifurcations in the cylinder response were observed as the flow velocity was increased above the threshold for the initial Hopf bifurc ation (fluidelastic instability), confirming similar findings from the oretical analyses. Responses with a primarily periodic component, as w ell as chaotic motions were obtained. Intermittency was found to be th e dominant route leading to chaos. The gap size at the support, when c oupled with initial cylinder preload, was found to have a profound eff ect on the resulting cylinder response. Hence, while nearly periodic o r borderline chaotic responses occurred for larger gap sizes, generali zed chaotic motions were prevalent for the smallest gap sizes tested.