A Study On The Flow-induced Vibration Of Tube Bundles

The flow-induced vibration of tube budles is an important case of flow-induced vibrations,which can be found widely in the structures with tube bundles,such as heat exchangers,condensers,steam generators,ocean drilling platform,and bridge bases.There are four main groups of mechanisms for flow-induced vibration: turbulent buffecting,acoustics resonance,fluid-elastic instability,and vortex shedding induced vibration.Among them,fluid-elastic instability and vortex shedding induced vibration are the most important.In this thesis,fluid-elastic instability and vortex shedding induced vibration were studied by the methods of experiments and numerical simulations.The research objects contained different patterns of tube bundles,single tube,and two tubes in tandem arrangement.Through the experiments,the effects which patterns,mass ratios,natural frequencies,and other parameters of tube bundles have on amplitudes,power spectral density functions,response frequencies,added mass coefficients,and other characteristics of tube bundles were obtained.According to the comprehensive analyses of the experimental results,some conclusions were obtained: the location of the monitored tube has an effect on the certain critical flow velocity value for the fluid-elastic instability;the larger the mass ratio of the tube bundle is,the higher the critical flow velocity for the fluid-elastic instability is;the critical flow velocity of the parallel triangular tube bundle for the fluid-elastic instability is larger than the critical flow velocity of the normal square tube bundle for the fluid-elastic instability;in the case of decreasing flow velocity,the larger the mass ratio,the broader velocity range where the tube bundle which has been in the state of fluid-elastic instability can keep on the state of fluid-elastic instability is,the parallel triangular tube bundle can keep on the state of the fluid-elastic instability in a broader flow velocity range than the normal square tube bundle dose,hysteresis phenomenon of amplitudes occurred in both the experiments about fluid-elastic instability and the experiments about vortex shedding induced vibration;no matter during the fluid-elastic instability experiments or during the vortex shedding induced vibration experiments,the amplitudes obtained from the lift direction were all larger than those obtained from the drag direction significantly.By the numerical simulations of the vortex-induced vibration of a single tube and the votex-induced vibration of the two tubes in tandem arrangement,the integrative characteristics of tube bundles were realized much more.In the structure of the two unequal-sized tubes in tandem arrangement,a large-radius tube was fixed upstream,and a small-radius tube was flexible downstream.The numerical simulation results show that the small-radius tube which is flexible downstream can keep on the state of large amplitude vibration in a broader flow velocity range than the single tube does;in the two unequal-sized tubes in tandem arrangement,the lift signal of the large-radius tube fixed upstream is a clear single frequency signal,however,the lift signal of the small-radius tube flexible downstream contains more than one frequency signal.This thesis can enrich the study of flow-induced vibration,and can provide theory basis for the designment and operation of tube-like equipments.