Investigation of Fluid-Elastic Instability in Tube Arrays at Low Mass Damping Parameters in Cross-Flow

2019 ◽  
Vol 142 (1) ◽  
Author(s):  
Kai Guo ◽  
Wei Xu ◽  
Zhanbin Jia ◽  
Wei Tan
Keyword(s):  
Critical Velocity ◽  
Transverse Direction ◽  
Cfd Simulation ◽  
Triangular Array ◽  
Elastic Instability ◽  
Streamwise Direction ◽  
Fluid Force ◽  
Force Coefficients ◽  
Tube Arrays ◽  
Low Mass

Abstract Fluid-elastic instability (FEI) is the most dangerous vibration mechanism in tube arrays. As the research shows in the recent years, the mechanism of FEI turns to be clear, but threshold prediction in low mass damping parameter (MDP) tube arrays is still not accurate because of the complexity of the instability mechanism. In this work, computational fluid dynamics (CFD) simulation is first validated by comparison with the water tunnel experiments in four kinds of tube arrangements and then extended to two-phase flow to get more data in low MDP range. Using fluid force coefficients calculated by CFD simulation, unsteady modeling of the tube model is established and the critical velocities match well with experiment and CFD simulation results. The effect of tube arrangement and Reynolds number on the fluid force coefficients and the predicted critical velocity is studied according to the unsteady flow theory. The results show that instability critical velocity of the normal triangular array can be underestimated at MDP lower than 1. When the frequency ratio (streamwise direction to transverse direction) decreases to below 0.8 in the rotated triangular array, the streamwise instability occurs earlier than transverse instability. The methods and conclusions in this paper can be used in FEI analysis in both streamwise direction and transverse direction.

Fluid Elastic Whirling of Tube Rows and Tube Arrays

1977 ◽  
Vol 99 (3) ◽  
pp. 457-460 ◽  
Author(s):  
R. D. Blevins
Keyword(s):  
Experimental Data ◽  
Control Volume ◽  
Fluid Force ◽  
Force Coefficients ◽  
Tube Arrays

Models are developed for the fluid force coefficients that determine the onset of whirling of tube rows and tube arrays. A control volume momentum analysis is employed. The results are in agreement with the available experimental data.

Motion-Dependent Fluid Force Coefficients for Tube Arrays in Crossflow

2001 ◽  
Vol 123 (4) ◽  
pp. 429-436 ◽  
Author(s):  
S. S. Chen ◽  
G. S. Srikantiah
Keyword(s):  
Excitation Amplitude ◽  
Steam Generators ◽  
Fluid Force ◽  
Force Coefficients ◽  
Fluid Forces ◽  
Stiffness Coefficients ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Fluid Damping ◽  
Series Of Experiments

Fluidelastic instability of tube arrays in crossflow is interesting academically and important in steam generators and heat exchangers. The key elements necessary to accurately predict fluidelastic instability of tube arrays in crossflow are motion-dependent fluid force coefficients. This paper presents several series of experiments that measure motion-dependent fluid forces for various tube arrays. Fluid damping and stiffness coefficients based on the unsteady flow theory were obtained as a function of reduced flow velocity, excitation amplitude, and Reynolds number, and the characteristics of motion-dependent fluid force coefficients were applied to provide some additional insights into fluidelastic instability.

Nonlinear Analysis of Rotordynamic Fluid Forces in the Annular Plain Seal by Using Extended Bulk-Flow Analysis: Influence of Static Eccentricity and Whirling Amplitude

2018 ◽  
Vol 141 (2) ◽  
Author(s):  
Koya Yamada ◽  
Atsushi Ikemoto ◽  
Tsuyoshi Inoue ◽  
Masaharu Uchiumi
Keyword(s):  
Perturbation Analysis ◽  
Flow Analysis ◽  
Flow Theory ◽  
Bulk Flow ◽  
Design Stage ◽  
Fluid Force ◽  
Force Coefficients ◽  
Fluid Forces ◽  
Static Eccentricity ◽  
Harmonic Components

Rotor-dynamic fluid force (RD fluid force) of turbomachinery is one of the causes of the shaft vibration problem. Bulk flow theory is the method for analyzing this RD fluid force, and it has been widely used in the design stage of machine. The conventional bulk flow theory has been carried out under the assumption of concentric circular shaft's orbit with a small amplitude. However, actual rotating machinery's operating condition often does not hold this assumption, for example, existence of static load on the machinery causes static eccentricity. In particular, when such a static eccentricity is significant, the nonlinearity of RD fluid force may increase and become non-negligible. Therefore, conventional bulk flow theory is not applicable for the analysis of the RD fluid force in such a situation. In this paper, the RD fluid force of the annular plain seal in the case of circular whirling orbit with static eccentricity is investigated. The case with both the significant static eccentricity and the moderate whirling amplitude is considered, and the perturbation analysis of the bulk-flow theory is extended to investigate the RD fluid force in such cases. In this analysis, the assumption of the perturbation solution is extended to both static terms and whirling terms up to the third order. Then, the additional terms are caused by the coupling of these terms through nonlinearity, and these three kinds of terms are considered in the extended perturbation analysis of the bulk flow theory. As a result, a set of nonlinear analytical equations of the extended perturbation analysis of the bulk flow theory, for the case with both the significant static eccentricity and the moderate whirling amplitude, is deduced. The RD fluid force for such cases is analyzed, and the occurrence of constant component, backward synchronous component, and super-harmonic components in the RD fluid force is observed in addition to the forward synchronous component. The representation of RD fluid force coefficients (RD coefficients) are modified for the case with significant static eccentricity, and the variation of RD fluid force coefficients for the magnitude of static eccentricity is analyzed. These analytical results of RD fluid force and its RD coefficients are compared with the numerical results using finite difference analysis and experimental results. As a result, the validity of the extended perturbation analysis of the bulk-flow theory for the case with both the significant static eccentricity and the moderate whirling amplitude is confirmed.

An Analysis of In-Flow Fluidelastic Instability Based on a Physical Insight

2014 ◽  
Author(s):  
Tomomichi Nakamura
Keyword(s):  
Flow Velocity ◽  
Flow Instability ◽  
Pressure Sensors ◽  
Measured Data ◽  
Critical Flow ◽  
Nonlinear Phenomenon ◽  
Critical Flow Velocity ◽  
Fluid Force ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic vibration of tube arrays caused by cross-flow has recently been highlighted by a practical event. There have been many studies on fluidelastic instability, but almost all works have been devoted to the tube-vibration in the transverse direction to the flow. For this reason, there are few data on the fluidelastic forces for the in-flow movement of the tubes, although the measured data on the stability boundary has gradually increased. The most popular method to estimate the fluidelastic force is to measure the force acting on tubes due to the flow, combined with the movement of the tubes. However, this method does not give the physical explanation of the root-cause of fluidelastic instability. In the work reported here, the in-flow instability is assumed to be a nonlinear phenomenon with a retarded or delayed action between adjacent tubes. The fluid force acting on tubes are estimated, based on the measured data in another paper for the fixed cylinders with distributed pressure sensors on the surface of the cylinders. The fluid force acting on the downstream-cylinder is assumed in this paper to have a delayed time basically based on the distance between the separation point of the upstream-cylinder to the re-attachment point, where the fluid flows with a certain flow velocity. Two models are considered: a two-cylinder and three–cylinder models, based on the same dimensions as our experimental data to check the critical flow velocity. Both models show the same order of the critical flow velocity and a similar trend for the effect of the pitch-to-diameter ratio of the tube arrays, which indicates this analysis has a potential to explain the in-flow instability if an adequate fluid force is used.

The Effect of Flat Bar Supports on Streamwise Fluidelastic Instability in Heat Exchanger Tube Arrays

2015 ◽  
Vol 137 (6) ◽  
Author(s):  
Marwan Hassan ◽  
David S. Weaver
Keyword(s):  
Sliding Friction ◽  
Chemical Plants ◽  
Streamwise Direction ◽  
Flow Induced Vibration ◽  
Direction Parallel ◽  
Short Period ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
Ambient Turbulence

Flow-induced vibration is an important criterion for the design of heat exchangers in nuclear, fossil, and chemical plants. Of the several known vibration excitation mechanisms, fluidelastic instability (FEI) is the most serious because it can cause tube failures in a relatively short period of time. Traditionally, FEI has been observed to occur in the direction transverse to the flow and antivibration bars have been used to stiffen the tubes against this motion. More recently, interest has increased in the possibility of FEI occurring in the streamwise direction, parallel to the flow. This is the subject of the present paper. Numerical simulations have been carried out to study the effects of tube-to-support clearance, tube sliding friction, tube-to-support preload, and ambient turbulence levels on the FEI threshold in the streamwise direction. As one would expect, increasing friction and tube preload against the support both tend to stabilize the tube against streamwise FEI. Importantly, the results also show that decreasing tube-support clearances destabilizes streamwise FEI while having little effect on transverse FEI. Increasing ambient turbulence levels also has the effect of destabilizing streamwise FEI.

Applicability of the Wavy-Wall Model of Fluidelastic Instability to a Normal Triangular Tube Array

2008 ◽  
Author(s):  
Julie Harel ◽  
Craig Meskell
Keyword(s):  
Experimental Data ◽  
Triangular Array ◽  
Phase Lag ◽  
Pressure Perturbation ◽  
Wavy Wall ◽  
Decay Function ◽  
Wall Model ◽  
Line Array ◽  
Tube Arrays ◽  
Fluidelastic Instability

The Yetisir and Weaver formulation of the Lever and Weaver “wavy-wall” model for fluidelastic instability in tube arrays has been implemented for both normal triangular and in-line square arrays. The sensitivity of this model to the input parameters (i.e. attachment and separation points, decay function and phase lag function) has been examined. It was found that variations in the decay function were most significant and that the model behaved similarly for both array types. The predicted surface pressure perturbation due to tube displacement has then been compared with experimental data. For the in-line array the model behaviour compared well, while for the normal triangular array, the predictions were not representative of the experimental data. It is concluded that while the Yetisir and Weaver model can be applied successfully to in-line square arrays, it is not appropriate for densely packed normal triangular arrays.

Flow Velocity Dependence of Damping in Tube Arrays Subjected to Liquid Cross-Flow

1981 ◽  
Vol 103 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. S. Chen ◽  
J. A. Jendrzejczyk
Keyword(s):  
Mathematical Modeling ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Elastic Instability ◽  
Velocity Dependence ◽  
Tube Arrays ◽  
Fluid Damping ◽  
Lift And Drag

Experiments are conducted to determine the damping for a tube in tube arrays subjected to liquid cross-flow; damping factors in the lift and drag directions are measured for in-line and staggered arrays. It is found that: 1) fluid damping is not a constant, but a function of flow velocity; 2) damping factors in the lift and drag directions are different; 3) fluid damping depends on the tube location in an array; 4) flow velocity-dependent damping is coupled with vortex shedding process and fluid-elastic instability; and 5) flow velocity-dependent damping may be negative. This study demonstrates that flow velocity-dependent damping is important. These characteristics should be properly taken into account in the mathematical modeling of tube arrays subjected to cross-flow.

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