Direct numerical simulation of flow-induced vibrations of a wavy cable at a low Reynolds number

Abstract

Previous studies have revealed that fluid induced forces and wake structure of a cylinder can be significantly modified by varying the cross-section size along its axis. However, the fluid dynamic characteristics behavior of a flexible cable with a sinusoidal wavy surface remains unclear. The current study endeavors to present a systematic investigation of flow-induced vibrations (FIV) of an infinitely long wavy cable with different wave amplitude (A=0.1D to 0.3D) and a constant spanwise wavelength λ=4π, by using a highly resolved direct numerical simulation employing a high-order spectral/hp element method at a Reynolds number of 100, corresponding to laminar flow state. A tensioned beam model with a tension value can trigger a single wave is selected to govern the dynamics of the wavy cables. In addition, the structural dynamics are initialized from a standing wave. The present study focuses on the effects of the wave amplitude on the cable wake and the structural dynamic response, including the transverse displacement, wake pattern, vortex formation length, energy transfer, vortex shedding frequency and flow separation angle. Two completely different vibration modes are identified from the numerical cases studied, and hence the wavy cable are divided into control failure (A<0.2D) and optimal wavy cable (0.2D⩽A⩽0.3D) classes, respectively. It is also revealed that the counter-rotating vortices observed in the optimal wavy cables play an important role in stabilizing the shear layer and elongating the vortex formation length. Furthermore, the three-dimensional wake patterns of the wavy cable are mainly caused by the variations of flow separation angle along its spanwise direction. For the optimal wavy cables, the separation point is almost fixed along its spanwise direction while is variable for the control failure cases.