Suppression of vortex-induced vibrations by fairings: A numerical study

摘要

Fairings are nearly neutrally buoyant devices, fitted along the axis of long circular risers to suppress vortex-induced vibrations (VIV) and possibly reduce the drag force. Here we study numerically how VIV can be practically eliminated by using free-to-rotate fairings. Since the rotational inertia is low for the fairings, direct numerical simulations based on standard fluid-structure interaction algorithms may fail because of the so-called added mass effect. To resolve this problem we introduce fictitious methods and successfully stabilize the simulations. We then investigate the effect of rotational friction C-f on the stabilization effect of the fairings. In particular through two-dimensional (2D) simulations we find that when the Reynolds number is low (Re=100), C-f=0 is the most effective choice in suppressing VIV. Moreover, at this low Reynolds number there exists a critical value of C-f around which large oscillations and non-symmetric trajectories are observed. On the other hand, at higher Reynolds number (Re=500) a different behavior emerges, i.e. VIV are suppressed continuously as C-f increases. At Re=1000, we perform 3D simulations to investigate the effects of three-dimensionality of the flow on the vibration and rotation responses. In this work we quantify numerically for the first time various salient features of free-to-rotate devices for VIV suppression and relate them to modified flow structures in the near wake. (C) 2015 Elsevier Ltd. All rights reserved.