Fluid-Structure Interaction Simulations of Flexible Cylinders in Confined Axial Flow

Abstract

Flexible cylinders surrounded by a fluid flow that is dominantly aligned with the axis of the cylinders can be found in several applications. Examples with a flow confined to a narrow region around the cylinder(s) can be found in tube bundles of heat exchangers and reactor cores and also in air-jet weaving machines. This research analyses the flow-induced vibration of these two different cases with flexible cylinders in confined axial flow using numerical fluid-structure interaction (FSI) simulations. The FSI simulations of both cases use a partitioned framework, meaning that a computational fluid dynamics (CFD) solver is coupled with a finite element analysis (FEA) structural solver. The dynamic and kinematic equilibrium conditions at the contact surface between the fluid and the structure are satisfied by performing coupling iterations between both solvers in each time step. Convergence of these iterations is accelerated using quasi-Newton coupling techniques. For the case of the tube bundle, the modal characteristics have been identified for a tube bundle when they are submerged in an axial fluid flow. Furthermore, different types of flow-induced vibration have been studied. The flow speed has been increased in an FSI simulation of a single cylinder surrounded by an annular fluid domain, resulting first in static buckling and then in flutter at higher flow speeds. For the case of the air-jet weaving machines, the cylinder represents a smooth yarn which is accelerated by an air jet in the main nozzle of the machine, consisting of a long tube with small diameter. FSI simulations of a yarn clamped at the upstream end have been performed using the arbitrary Lagrangian-Eulerian formulation with deforming grids in the fluid domain. This work demonstrates the feasibility of analyzing and predicting flow-induced vibration of cylinders in confined axial flow by performing FSI simulations. The results of simulations are compared with those of experiments for tubes in axial flow and for a yarn in a nozzle of an air-jet weaving machine.