Fluid-Elastic Instability Tests on Parallel Triangular Tube Bundles with Different Mass Ratio Values under Increasing and Decreasing Flow Velocities

Xu Zhang,Luhong Zhang,Bin Jiang,Xiaoming Xiao

doi:10.1155/2016/1680218

Abstract

To study the effects of increasing and decreasing flow velocities on the fluid-elastic instability of tube bundles, the responses of an elastically mounted tube in a rigid parallel triangular tube bundle with a pitch-to-diameter ratio of 1.67 were tested in a water tunnel subjected to crossflow. Aluminum and stainless steel tubes were tested, respectively. In the in-line and transverse directions, the amplitudes, power spectrum density functions, response frequencies, added mass coefficients, and other results were obtained and compared. Results show that the nonlinear hysteresis phenomenon occurred in both tube bundle vibrations. When the flow velocity is decreasing, the tubes which have been in the state of fluid-elastic instability can keep on this state for a certain flow velocity range. During this process, the response frequencies of the tubes will decrease. Furthermore, the response frequencies of the aluminum tube can decrease much more than those of the stainless steel tube. The fluid-elastic instability constants fitted for these experiments were obtained from experimental data. A deeper insight into the fluid-elastic instability of tube bundles was also obtained by synthesizing the results. This study is beneficial for designing and operating equipment with tube bundles inside, as well as for further research on the fluid-elastic instability of tube bundles.

Highlights

Flow-induced vibration remains a concern in designing tube-like structures, such as shell-and-tube heat exchangers, nuclear steam generators, and tubular reactors
When the flow exceeds a certain critical velocity, fluidelastic instability occurs with the rapid increase in the amplitude of the tube bundle
To characterize the magnitude of tube vibrations, the rootmean-square tube amplitude expressed as a percentage of the tube diameter was plotted against reduced pitch flow velocity U∗ obtained from the following equations: UP

Summary

Introduction

Flow-induced vibration remains a concern in designing tube-like structures, such as shell-and-tube heat exchangers, nuclear steam generators, and tubular reactors. Flowinduced vibration of tube bundles mainly contains fluidelastic instability, vortex shedding, turbulent buffeting, and acoustic resonance [1,2,3,4]. Among these characteristics, fluidelastic instability, which is a self-excited vibration, represents the most possible danger because of its potential for extremely large vibration amplitudes. When the flow exceeds a certain critical velocity, fluidelastic instability occurs with the rapid increase in the amplitude of the tube bundle. The tube bundle may be damaged by large-amplitude vibrations in a short time. The mechanism of fluid-elastic instability should be studied for predicting and avoiding dangerous flow conditions in tube-like structures

Methods

Results

Conclusion