Numerical studies of a freely vibrating cylinder in a cross-flow

A numerical method with four different components is used to simulate the f low-induced vibration at the mid-span of a long slender cylinder, simply su pported at both ends, and placed in a uniform cross-flow. The incompressibl e laminar flow, which is assumed to be two-dimensional, is calculated using a finite element method and the cylinder motion is analysed by a two-degre e-of-freedom model (or a spring-damper-mass model). The fluid-cylinder inte raction is resolved by an iterative time marching method and the calculated time series are analysed by the ARMA technique. The cases examined include stationary as well as freely vibrating cylinders in a cross-flow. In the v ibrating cylinder case, resonance and off-resonance situations are consider ed. Comparisons are made with experimental measurements for stationary cyli nders as well as for a freely vibrating cylinder at off-resonance. The redu ced velocity examined varies from 3.6 to 9.2, corresponding to a Reynolds n umber (Re) range of 2000-5000. At least two different mass ratios and two d ifferent reduced damping parameters are investigated. The numerical method is capable of replicating the Strouhal number correctly in the Re range inv estigated. A comparison of the calculated cylinder dynamics with measuremen ts tends to support the results obtained using the present approach. This i s true for both stationary and freely vibrating cylinders over the range of parameters considered. Therefore, the present numerical approach can be us ed to analyse flow-induced vibration problems in the range of parameters in vestigated, in spite of the fact that the wake flow is three-dimensional an d turbulent. (C) 2001 Academic Press.