Multiple Stability Boundaries of Tubes in a Normal Triangular Cylinder Array

Abstract

This paper reports on experiments using a normal triangular cylinder array with a pitch-to-diameter ratio of 1.25 in air-cross-flow. The array consists of 18 tubes, in which 9 freely suspended tubes are linear iso-viscoelastically mounted. This unique tube mounting enables the linear damping of 9 cylinders (4, 3 and 2 cylinders in the first, second, and third cylinder row, respectively) to be continuously varied over a wide mass-damping parameter range of 10 < μδ/(ρd2 ) < 80. The experimentally observed phenomenon are correlated with nonlinear vibration theory terminology in order to improve the characterization of the excitation mechanisms. Experimental results are presented showing three stability boundaries for one flexibly mounted tube in an otherwise fixed array, as was predicted by Lever and Weaver’s “wavy wall channel model.” Flow visualization, for that arrangement, shows that their model describes the actual fluid flow past the tube reasonably well. Furthermore, multiple stability boundaries for small groups of flexibly mounted cylinders in an otherwise fixed cylinder array have, for the first time, been measured.