The Numerical Simulation On Two Way Fluid Structure Coupling Mechanism Of Flow Induced Vibration For Liquid Filled Heat Transfer Tube

Flow-induced vibration and water hammer is often the key factor leading to the flow induced failure of heat exchanger, and flow-induced vibration and water hammer depends on the two-way fluid-structure interaction. However, the flow field mutation near the wall of tubes may induce the vibration of heat transfer tubes, the wall boundary vibration deformation accompanied by flow-induced vibration also make the near-wall velocity field accelerate, and mutual coupling of these two movements make the two-way fluid-structure interaction dynamical behavior of heat transfer tubes be extremely complex. Revealing the two-way fluid-structure coupling mechanism of flow induced vibration is the premise of establishing the shell and tube heat exchanger flow-induced vibration failure theory. So far, the numerical simulation of two-way fluid-structure interaction in flow-induced vibration remains an engineering and technical challenge, which related research is rarely reported, and the two-way fluid-structure coupling mechanism has not yet been fully understood. In response to this engineering background, the two-way fluid-structure coupling theoretical model of the Inner and outer filling liquid heat transfer tube was established in this paper, the two-way fluid-structure coupling mechanism in flow-induced vibration of heat transfer tube was studied, and the key regulatory parameters of two-way fluid-structure interaction was cleared, which laid the theoretical foundation of the shell and tube heat exchanger flow-induced vibration failure theory. This research has the following innovative results.(1) In response to the two-way fluid-structure coupling process in flow-induced vibration of heat transfer tube, on the basis of Arbitrary Lagrangian Eulerian method and reasonable assumptions, the full three-dimensional theoretical model describing the two-way fluid-structure coupling process in flow-induced vibration of heat transfer tube was established.(2) The comparative study between dry modal analysis of empty tube and the wet modal analysis of fluid-structure interaction shows that natural frequencies and mode shapes of two modal analysis methods were significantly different, the natural frequency of the wet modal analysis is generally lower than the natural frequency of dry modal analysis, a difference of two natural frequency is up to 37-54%, and the traditional dry modal analysis of empty tube which is widely used at home and abroad can not truly reflect the dynamic characteristics and vibration mode of heat transfer tube with filling liquid inside and outside.(3) The mechanism scientific hypothesis was first proposed in which the natural frequency of heat transfer tube with filling liquid inside and outside is controlled by the fluid gravity effect and the fluid-structure interaction, and is reduced with increasing of the fluid gravity effect and the fluid-structure interaction. The correctness of the scientific hypothesis was verified by means of the simulation research on the influencing rules of the fluid gravity effect and the fluid-structure interaction on the natural frequency of the wet modal analysis(4) The relationship between the dynamic response of heat transfer tube flow-induced vibration and the key influencing parameters is established by means of the numerical simulation research, the results show that the dynamic response is increased with increasing of pulsating flow amplitude and frequency, And the dynamic response of heat transfer tube under two-way fluid-structure interaction is significantly greater than the dynamic response of heat transfer tube under one-way fluid-structure interaction.(5)The dynamic response mechanism assumptions was first proposed in which the dynamic response of flow-induced vibration is controlled by the two-way fluid-structure interaction induced water hammer pressure on well, and its water hammer pressure depends on inlet velocity mutations and wall boundary vibration deformation movement, which is increased with increasing of inlet velocity mutations and wall boundary vibration deformation movement.(6) The two-way fluid-structure coupling mechanism of heat transfer tube with filling liquid inside and outside was revealed, the results show that with the increase of the pulsating flow frequency and amplitude, the greater the inlet velocity mutation, which make flow-induced vibration of heat transfer tube enhancement, and the wall boundary vibration deformation movement accompanied by flow-induced vibration also make near-wall velocity field of heat transfer tube sudden increase, which further make the wall water hammer pressure of heat transfer tubes increase. Because the pulsating fluid flow induced the wall boundary vibration deformation movement, and the wall boundary vibration deformation movement will induce near- flow field sudden acceleration,it is that the coupling effect between pulsating fluid flow and wall boundary vibration deformation movement makes the wall water hammer of two-way fluid-structure coupling heat transfer tube strengthen with increasing of pulsating fluid flow frequency and amplitude.(7) The theoretical premise of accurately predicting of the flow-induced vibration dynamic response is establishing of theory describing two-way fluid-structure coupling process and its numerical simulation method, so as to reflect truly the reverse effect of the wall boundary vibration deformation movement on the near-wall velocity field. The dynamic response of one-way fluid-structure coupling method widely used at home and abroad is 2 to 4.87 times smaller than the dynamic response of two-way fluid-structure coupling method,which is not safe.