Stability effects in a normal triangular cylinder array

Abstract

Fluid-elastic vibrations in tube bundles are often responsible for major damage and very high shutdown costs. The onset is manifested by a rapid increase in the tube vibration amplitude at a particular critical flow velocity and is strongly dependent upon various physical parameters. In this paper, experimental results showing a second stability boundary for a flexibly mounted cylinder in an otherwise fixed cylinder array are presented. It is shown that minor variations of the array geometry affect its vibration mode. The stability boundaries, for various configurations of flexibly mounted and fixed cylinders in the array, have been measured. The resulting stability boundaries are plotted as functions of the mass-damping parameter and amplitude-diameter ratio in stability diagrams. The results are critically compared with known results from the literature. A closed-circuit wind tunnel with a 1·5 m diameter, 2·1 m long test section is used for the tests. The eighteen 80 mm × 800 mm aluminium cylinders in the multi-row normal triangular array have a pitch-to-diameter ratio of 1·25 and are, when not fixed, linear iso-viscoelastically mounted. Additionally, the linear damping of nine cylinders (4, 3 and 2 cylinders in the first, second and third cylinder row, respectively) can be continuously varied over the wide mass-damping parameter range of 10 2