Fluid-elastic Instability Study Of Flow-induced Vibration In Tube Bundles

Flow-induced vibration of tube bundles can result in the consequent fretting-wear damage,which is common the symptomatic problem in process equipment.Normally,several vibration excitation mechanisms are considered in tube bundles,namely:periodic wake shedding,random excitation,fluid-elastic instability and acoustic resonance.Fluid-elastic instability is the cause of the most severe vibration response,which lead to the rapid wear and tear of the tube at the support.At present,there are many experimental researches on the fluid-elastic instability,but the design principles have not been given a unified conclusion due to the complexity of the mechanism.Therefore,the study of fluid-elastic instability needs further development,which provides more theoretical basis for the design of heat exchanger.First of all,an innovative experimental platform for the vibration of tube bundles which is induced by single-phase flow and two-phase flow is designed and built.During the experiment process,the fluid-elastic instability of four kinds of tube bundles(square and normal triangular arrangement,pitch-to-dimeter ratio of 1.28 and 1.33)are studied and the vibration characteristics are also researched in single-phase and two-phase cross-flow.At the same time,CFD and Fluid-solid coupling method are used to simulate the fluid-elastic instability of tube bundles.The information of flow field and structure field are obtained and analyzed.The simulation complements the contents of the experimental study,which is utilizable to investigate the fluid-elastic instability.Results showed that under the same conditions,the square configuration is more stable than the normal triangular configuration whether in a single-phase flow or in a two-phase flow.For the square configuration,the instability constant K recommends to be 4.0 and 3.4 for the normal triangular configuration,when the void fraction is less than 80%and the pitch-to-diameter is not less than 1.28.Meantime,the main vibration direction of the fluid-elastic instability of the tube bundles changes from the drag force direction to the lift direction.In the tube configuration,the difficulty degree of fluid elastic instability occurrence is:the normal square is the hardest,the normal triangular is the second,the rotated square is the third,and the rotated triangular is the easiest.In a certain range,with the increase of the pitch-to-diameter,the critical flow velocity of fluid-elastic instabilities increases.