Strouhal Number for Vortex-Induced Vibration Excitation of Long Slender Structures

Abstract

A variety of contemporary test data for elastically mounted cylinders, with the freedom to oscillate under one degree-of-freedom (1DOF, i.e., cross-flow) and 2DOF (i.e., cross-flow and in-line) were evaluated and compared against the conventional Strouhal number relationship. It is well established for vortex-induced vibration (VIV) that the eddy-shedding frequency will synchronize with the near-resonant motions of a dynamically oscillating cylinder, such that the resultant bandwidth of lock-in exhibits a wider range of effective Strouhal numbers than that reflected in the narrow-banded relationship about a mean of 0.2. However, whilst cylinders oscillating under 1DOF exhibit a mean Strouhal number of 0.2 consistent with fixed/stationary cylinders, cylinders with 2DOF exhibit a much lower mean Strouhal number of around 0.14–0.15.