Flow Induced Vibration in a 2D Mixed Geometry Tube Array

The work reported here is part of a study on fluid-structure interaction in mixed-geometry tube arrays. In our previous study, flow in a mixed geometry tube array was found to exhibit significantly complex dynamical behavior compared to the component arrays of basic symmetry. A series of bifurcations as a result of changing the system parameter, Reynolds number, was found. The results indicated that the periodic coherent structures, normally found in symmetric tube arrays, are no longer stable, and thus the Strouhal number may not be a characteristic parameter or feature for mixed geometry tube arrays, unlike symmetrical arrays. In this work, flow-induced vibration in a mixed-geometry tube array with a transverse spacing ratio of 1.3 and a longitudinal spacing ratio of 1.5 was investigated. In the study, the transverse vibration response of a single flexible tube within the parallel triangle section in the mixed-geometry tube array is considered. Large amplitude lift and transverse displacement responses emerge as the coupled system transitions to fluidelastic instability and possible lock-in. The response evolves through 2:1 lock-in and a subsequent partial desynchronization, during which the vibration level remains persistently high. At higher velocities, flow periodicity and fluidelastic instability coexist; however, the lift spectrum is dominated by a pronounced third-harmonic component associated with wake flow nonlinear dynamics.