Resumo:
A purely Lagrangian Discrete Vortex Method (DVM) with a roughness model is employed to numerically simulate the two-dimensional, incompressible, unsteady flow around two tandem circular cylinders of equal diameter immersed in an incident flow. The downstream cylinder is located in the wake interference region of the upstream one for streamwise center-to-center distance between two cylinders of L=5D (D is the cylinder diameter). The streamwise spacing ratio L/D=5 is greater than the critical spacing L/D=4, the latter characterizes the known bistable flow for two immovable cylinders, where two values of drag coefficient are identified for two different flow patterns; namely, reattachment-flow and jump-flow regimes for the downstream cylinder. In this work, the downstream cylinder is forced to vibrate transversely in the wake of another fixed tandem cylinder aiming to investigate a regime of Wake-Induced Vibration (WIV) at Re=6.5 x 104. The literature has reported that WIV is a phenomenon resulting from the interaction between the incoming wake and the downstream flexible structure, in which the downstream cylinder vibrates significantly over a wide range of reduced velocities and, additionally, the cross-flow fluid force is not in phase with the body’s motion. The non-dimensionalized vibration amplitude is fixed at A/D=0.15 and the reduced velocity is adopted as VR=5. The phenomenon of WIV appears combined with a resonant regime, in which the downstream cylinder vibrates at the resonant velocity similar to the Vortex-Induced Vibration (VIV) of a single cylinder. For the streamwise spacing ratio of L/D=5, the individual resonant regime is captured for both smooth surfaces. The main contribution of the present research is to show that the variation of downstream cylinder roughness desynchronizes the VIV and WIV regimes, and also promotes transition between them.
