Numerical Simulation of Baffle-Supported Tube Bundle Vibration by the Method of Finite Differences

Abstract

Tube bundles in heat exchangers are often damaged due to flow-induced vibrations. To simulate the fluid-structure interaction between the tubes and the flow field, which seems to be the only reliable way to predict flow-induced vibration of tube bundles, a coupled numerical solver for the governing Navier-Stokes equations of the flow field as well as for the structural response has to be used. Since commercial codes still require a large computational effort to calculate the fluid-structure interaction, one has to develop special program codes for certain technical problems. This paper deals with a numerical method to calculate the structural response of baffle-supported heat exchanger tubes due to outer forces such as flow and contact forces. The equations of motion for a cylindrical tube including torsional movement are developed. They are discretized in space by the means of Finite Differences and in time by Newmark′s method of constant acceleration. Non-linear frictional impact forces due to the baffle supports are introduced as additional line loads and line moments. Flow forces at this stage of development are modeled by simplified assumptions concerning vortex shedding. Numerical examples show the consistency of the calculated solutions. The algorithm is stable and converges for parameters of practical importance. Only little mathematical effort is needed compared to the Finite Element technique or modal analysis. A Navier-Stokes flow solver already developed can now be integrated into the vibration simulation code.