Flow-induced vibrations in heat exchanger tubes have led to numerous accidents and economic losses in the past. Fluidelastic instability is the most critical flow-induced vibration mechanism in heat exchangers. Both e...Flow-induced vibrations in heat exchanger tubes have led to numerous accidents and economic losses in the past. Fluidelastic instability is the most critical flow-induced vibration mechanism in heat exchangers. Both experimental and computational studies conducted to determine fluidelastic instability were presented in this paper. In the experiment, a water channel was built, and a closely packed normal square tube array with a pitch-to-diameter ratio of 1.28 was tested, and significant fluidelastic instability was observed. A numerical model adopting large-eddy simulation and moving mesh was established using ANSYS CFX, and results showed good agreement with the experimental findings. The vibration behaviors of fluidelastic instability were discussed, and results showed that the dominant vibration direction of the tubes changed from streamwise to transverse beyond a critical velocity. A 180° phase lag between adjacent tubes was observed in both the experiment and simulations. Normal and rotated square array cases with pitch-to-diameter ratios of 1.28 and 1.5 were also simulated. The results of this study provide better insights into the vibration characteristics of a square tube array and will help improve the fundamental research and safety design of heat exchangers.展开更多
Fluidelastic instability is destructive in tube bundles subjected to cross flow.Flow channel model proposed by Leaver and Weaver is well used for modeling this problem.However,as the tube motion is supposed to be harm...Fluidelastic instability is destructive in tube bundles subjected to cross flow.Flow channel model proposed by Leaver and Weaver is well used for modeling this problem.However,as the tube motion is supposed to be harmonic,it may not simulate the general dynamic behaviors of tubes.To improve this,a model with arbitrary tube motion is proposed by Hassan and Hayder.While,due to involving in the time delay term,the stability problem cannot be solved by the eigenvalue scheme,and time domain responses of the tube have to be obtained to assess the instability threshold.To overcome this weakness,a new approach based on semi-discretizing method(SDM)is proposed in this study to make the instability threshold be predicted by eigenvalues directly.The motion equation of tube is built with considering the arbitrary tube motion and the time delay between fluid flow and tube vibration.A time delay integral term is derived and the SDM is employed to construct a transfer matrix,which transforms the infinite dimensional eigenvalue problem into a finite one.Hence the stability problem become solvable accordingly.With the proposed method,the instability threshold of a typical square tube array model is predicted,and the influences of system parameters on stability are also discussed.With comparing with prior works,it shows significant efficiency improvement in prediction of the instability threshold of tube bundles.展开更多
The influence of the squeeze film between the tube and the support structure on flow-induced vibrations is a critical factor in tube bundles subjected to two-phase cross-flow.This aspect can significantly alter the th...The influence of the squeeze film between the tube and the support structure on flow-induced vibrations is a critical factor in tube bundles subjected to two-phase cross-flow.This aspect can significantly alter the threshold for fluidelastic instability and affect heat transfer efficiency.This paper presents a mathematical model incorporating the squeeze film force between the tube and the support structure.We aim to clarify the mechanisms underlying fluidelastic instability in tube bundle systems exposed to two-phase flow.Using a self-developed computer program,we performed numerical calculations to examine the influence of the squeeze film on the threshold of fluidelastic instability in the tube bundle system.Furthermore,we analyzed how the thickness and length of the squeeze film affect both the underlying mechanisms and the critical velocity of fluidelastic instability.展开更多
A fully Lagrangian algorithm for numerical simulation of fluid-elastic structure interaction(FSI)problems is developed based on the Smoothed Particle Hydrodynamics(SPH)method.The developed method corresponds to incomp...A fully Lagrangian algorithm for numerical simulation of fluid-elastic structure interaction(FSI)problems is developed based on the Smoothed Particle Hydrodynamics(SPH)method.The developed method corresponds to incompressible fluid flows and elastic structures.Divergence-free(projection based)incompressible SPH(ISPH)is used for the fluid phase,while the equations of motion for structural dynamics are solved using Total Lagrangian SPH(TLSPH)method.The temporal pressure noise can occur at the free surface and fluid-solid interfaces due to errors associated with the truncated kernels.A FSI particle shifting scheme is implemented to produce sufficiently homogeneous particle distributions to enable stable,accurate,converged solutions without noise in the pressure field.The coupled algorithm,with the addition of proposed particle shifting scheme,is able to provide the possibility of simultaneous integration of governing equations for all particles,regardless of their material type.This remedy without need for tuning a new parameter,resolves the unphysical discontinuity beneath the interface of fluid-solid media.The coupled ISPH-TLSPH scheme is used to simulate several benchmark test cases of hydro-elastic problems.The method is validated by comparison of the presented results with experiments and numerical simulations from other researchers.展开更多
基金High-performance Computing Center of Tianjin Universitysupported by the Natural Science Foundation of China(No.21606164)
文摘Flow-induced vibrations in heat exchanger tubes have led to numerous accidents and economic losses in the past. Fluidelastic instability is the most critical flow-induced vibration mechanism in heat exchangers. Both experimental and computational studies conducted to determine fluidelastic instability were presented in this paper. In the experiment, a water channel was built, and a closely packed normal square tube array with a pitch-to-diameter ratio of 1.28 was tested, and significant fluidelastic instability was observed. A numerical model adopting large-eddy simulation and moving mesh was established using ANSYS CFX, and results showed good agreement with the experimental findings. The vibration behaviors of fluidelastic instability were discussed, and results showed that the dominant vibration direction of the tubes changed from streamwise to transverse beyond a critical velocity. A 180° phase lag between adjacent tubes was observed in both the experiment and simulations. Normal and rotated square array cases with pitch-to-diameter ratios of 1.28 and 1.5 were also simulated. The results of this study provide better insights into the vibration characteristics of a square tube array and will help improve the fundamental research and safety design of heat exchangers.
基金The support from the National Natural Science Foundation of China(No.11672179)is greatly acknowledged.
文摘Fluidelastic instability is destructive in tube bundles subjected to cross flow.Flow channel model proposed by Leaver and Weaver is well used for modeling this problem.However,as the tube motion is supposed to be harmonic,it may not simulate the general dynamic behaviors of tubes.To improve this,a model with arbitrary tube motion is proposed by Hassan and Hayder.While,due to involving in the time delay term,the stability problem cannot be solved by the eigenvalue scheme,and time domain responses of the tube have to be obtained to assess the instability threshold.To overcome this weakness,a new approach based on semi-discretizing method(SDM)is proposed in this study to make the instability threshold be predicted by eigenvalues directly.The motion equation of tube is built with considering the arbitrary tube motion and the time delay between fluid flow and tube vibration.A time delay integral term is derived and the SDM is employed to construct a transfer matrix,which transforms the infinite dimensional eigenvalue problem into a finite one.Hence the stability problem become solvable accordingly.With the proposed method,the instability threshold of a typical square tube array model is predicted,and the influences of system parameters on stability are also discussed.With comparing with prior works,it shows significant efficiency improvement in prediction of the instability threshold of tube bundles.
基金financially supported by the National Natural Science Foundation of China(Grant No.12072336).
文摘The influence of the squeeze film between the tube and the support structure on flow-induced vibrations is a critical factor in tube bundles subjected to two-phase cross-flow.This aspect can significantly alter the threshold for fluidelastic instability and affect heat transfer efficiency.This paper presents a mathematical model incorporating the squeeze film force between the tube and the support structure.We aim to clarify the mechanisms underlying fluidelastic instability in tube bundle systems exposed to two-phase flow.Using a self-developed computer program,we performed numerical calculations to examine the influence of the squeeze film on the threshold of fluidelastic instability in the tube bundle system.Furthermore,we analyzed how the thickness and length of the squeeze film affect both the underlying mechanisms and the critical velocity of fluidelastic instability.
文摘A fully Lagrangian algorithm for numerical simulation of fluid-elastic structure interaction(FSI)problems is developed based on the Smoothed Particle Hydrodynamics(SPH)method.The developed method corresponds to incompressible fluid flows and elastic structures.Divergence-free(projection based)incompressible SPH(ISPH)is used for the fluid phase,while the equations of motion for structural dynamics are solved using Total Lagrangian SPH(TLSPH)method.The temporal pressure noise can occur at the free surface and fluid-solid interfaces due to errors associated with the truncated kernels.A FSI particle shifting scheme is implemented to produce sufficiently homogeneous particle distributions to enable stable,accurate,converged solutions without noise in the pressure field.The coupled algorithm,with the addition of proposed particle shifting scheme,is able to provide the possibility of simultaneous integration of governing equations for all particles,regardless of their material type.This remedy without need for tuning a new parameter,resolves the unphysical discontinuity beneath the interface of fluid-solid media.The coupled ISPH-TLSPH scheme is used to simulate several benchmark test cases of hydro-elastic problems.The method is validated by comparison of the presented results with experiments and numerical simulations from other researchers.
