Numerical simulation of vortex-induced vibration of four circular cylinders in a square configuration

Two-degree-of-freedom Vortex-Induced Vibration (VIV) of four rigidly coupled circular cylinders in a square configuration is investigated numerically. Two-dimensional Reynolds-Averaged Navier-Stokes equations and SST k-omega turbulence equations are solved using a finite element method. Simulations are carried out for flow approaching angles of alpha = 0 degrees, 15 degrees, 30 degrees and 45 degrees and the reduced velocities ranging from 1 to 20 with an interval of 1. The Reynolds number ranges from 1000 to 20 000. The numerical results show that the approaching angle has significant effects on the response of the four-cylinder system. The lock-in region for alpha = 15 degrees is the widest (between 3 <= V-r <= 12) among the other cases investigated, while the lock-in region for alpha = 45 degrees is the narrowest (between 2 <= V-r <= 4). For alpha = 0 degrees, the vibration is generally irregular in the lock-in region. Regular and periodic vibrations are observed in the lock-in zone for approaching angles except alpha = 0 degrees, although the hydrodynamic forces, especially those on the two downstream cylinders, are very irregular. (c) 2012 Elsevier Ltd. All rights reserved.