Fluidelastic Instability of an Array of Tubes Preferentially Flexible in the Flow Direction Subjected to Two-Phase Cross Flow

2005 ◽  
Vol 128 (1) ◽  
pp. 148-159 ◽  
Author(s):  
R. Violette ◽  
M. J. Pettigrew ◽  
N. W. Mureithi
Keyword(s):  
Flow Direction ◽  
Cross Flow ◽  
Two Phase ◽  
Direction Parallel ◽  
Array Configuration ◽  
Fluidelastic Instability ◽  
Out Of Plane ◽  
Plane Direction ◽  
Almost All ◽  
Flexible Tubes

Almost all the available data about fluidelastic instability of heat exchanger tube bundles concerns tubes that are axisymmetrically flexible. In those cases, the instability is found to be mostly in the direction transverse to the flow. Thus, the direction parallel to the flow has raised less concern in terms of bundle stability. However, the flat bar supports used in steam generator for preventing U-tube vibration may not be as effective in the in-plane direction than in the out-of-plane direction. The possibility that fluidelastic instability can develop in the flow direction must then be assessed. In the present work, tests were done to study the fluidelastic instability of a cluster of seven tubes much more flexible in the flow direction than in the lift direction. The array configuration is rotated triangular with a pitch to diameter ratio of 1.5. The array was subjected to two-phase (air-water) cross flow. Fluidelastic instability was observed when the flexible tubes were located at the center of the test section and also when the seven flexible tubes were placed over two adjacent columns. No instability was found for a single flexible tube in a rigid array, nor for the case where the seven flexible tubes were placed in a single column. Tests were also done with tubes that are axisymmetrically flexible for comparison purposes. It was found that fluidelastic instability occurs at higher velocities when the tubes are flexible only in the flow direction. These results and additional wind tunnel results are compared to existing data on fluidelastic instability. Two-phase flow damping results are also presented in this paper.

Two-Phase Flow Induced Vibration of an Array of Tubes Preferentially Flexible in the Flow Direction

2005 ◽  
Author(s):  
R. Violette ◽  
N. W. Mureithi ◽  
M. J. Pettigrew
Keyword(s):  
Natural Frequencies ◽  
Flow Direction ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Phase Flow ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Array Configuration ◽  
Fluidelastic Instability ◽  
Existing Data

Tests were done to study the fluidelastic instability of a cluster of seven cylinders much more flexible in the flow direction than in the lift direction. The array configuration is rotated triangular with a pitch to diameter ratio of 1.5. The array was subjected to two-phase (air-water) cross flow. Cylinder natural frequencies of 14 and 28 Hz were tested. Fluidelastic instabilities were observed at 65, 80, 90 and 95% void fraction albeit at a somewhat higher flow velocity than that expected for axisymetrically flexible arrays. These results and additional wind tunnel results are compared to existing data on fluidelastic instability.

Fluidelastic Instability and Work-Rate Measurements of Steam-Generator U-Tubes in Air–Water Cross-Flow

2005 ◽  
Vol 127 (1) ◽  
pp. 84-91 ◽  
Author(s):  
V. P. Janzen ◽  
E. G. Hagberg ◽  
M. J. Pettigrew ◽  
C. E. Taylor
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Two Phase ◽  
Void Fractions ◽  
Wide Range ◽  
Fluidelastic Instability ◽  
Out Of Plane ◽  
Plane Direction ◽  
First Time ◽  
Support Work

The dynamic response of U-tubes to two-phase cross-flow has been studied in tests involving a simplified U-tube bundle with a set of flat-bar supports at the apex, subjected to air–water cross-flow over the mid-span region. Tube vibration and the interaction between tubes and supports were measured over a wide range of void fractions and flow rates, for three different tube-to-support clearances. The vibration properties and tube-to-support work-rates could be characterized in terms of the relative influence of fluidelastic instability and random-turbulence excitation. For the first time, in a U-bend tube bundle with liquid or two-phase flow, fluidelastic instability was observed both in the out-of-plane and in the in-plane direction. This raises the possibility of higher-than-expected tube-to-support work-rates for U-tubes restrained by flat bars, particularly if fluidelastic instability, random turbulence and loose supports combine adversely.

An unsteady model for fluidelastic instability in an array of flexible tubes in two-phase cross-flow

2015 ◽  
Vol 285 ◽  
pp. 58-64 ◽  
Author(s):  
Nai-bin Jiang ◽  
Bin Chen ◽  
Feng-gang Zang ◽  
Yi-xiong Zhang
Keyword(s):  
Cross Flow ◽  
Two Phase ◽  
Fluidelastic Instability ◽  
Flexible Tubes

A Quasi-Steady In-Plane Fluidelastic Instability Analysis of a Rotated Triangular Tube Array in Two-Phase Cross Flow

2018 ◽  
Author(s):  
Stephen Olala ◽  
Njuki Mureithi
Keyword(s):  
Time Delay ◽  
Degrees Of Freedom ◽  
Dynamic Test ◽  
Cross Flow ◽  
Two Phase ◽  
Unsteady Forces ◽  
Fluidelastic Instability ◽  
Fluid Coupling ◽  
Flexible Tubes ◽  
Experimental Effort

In-plane fluidelastic instability is a dynamic phenomenon requiring fluid coupling of at least two degrees-of-freedom, in this case, at least two flexible tubes. Due to the nature of the mechanism causing streamwise fluidelastic instability, a purely experimental or an unsteady determination would require intensive experimental effort. As a compromise between experimental effort and prediction accuracy, the quasi-steady model is used in the current study. In the present work, previously measured quasi-steady and unsteady forces are used to estimate the time delay first between the displacement of an oscillating tube and the forces generated on itself then the time delay between the displacement of a central oscillating tube and the forces induced on the adjacent tubes. The estimated time delays are then used together with drag coefficients and derivatives to predict the in-plane fluidelastic instability in a rotated triangular tube array of P/D = 1.5 subjected to two-phase flow. The results closely replicate dynamic test results and confirm the predominance of the stiffness controlled mechanism and the potential of the quasi-steady model in accurately predicting streamwise fluidelastic instability in arrays subjected to two-phase flows.

The Effect of Angle of Attack on the Fluidelastic Instability of Tube Bundle Subjected to Two-Phase Cross-Flow

2009 ◽  
Author(s):  
T. F. Joly ◽  
N. W. Mureithi ◽  
M. J. Pettigrew
Keyword(s):  
Tube Bundle ◽  
Angle Of Attack ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Test Results ◽  
Two Phase ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
Flexible Tubes ◽  
Existing Data

Tests were done to study the effect of angle of attack on the fluidelastic instability of a fully flexible tube bundle subjected to two-phase (Air-Water) cross-flow. A test array having nineteen flexible tubes in a rotated triangular configuration with a pitch-to-diameter ratio of 1.5 was tested. Four different angles of attack ranging for 0 degree (inline flexibility) through 30 and 60 degrees to 90 degrees (transverse flexibility) were studied. For each angle of attack several homogeneous void fractions have been tested (70%, 80%, 90%, and 95%). Stability test results show that the angle of attack strongly affect the tube bundle dynamic behavior. The different mechanisms underlying the fluidelastic instability are highlighted and the results compared to existing data on fluidelastic instability.

scholarly journals On Damping and Fluidelastic Instability in a Tube Bundle Subjected to Two-Phase Cross-Flow

2007 ◽  
Author(s):  
Joaquin E. Moran ◽  
David S. Weaver
Keyword(s):  
Flow Regime ◽  
Void Fraction ◽  
Tube Bundle ◽  
Damping Ratio ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Phase Changes ◽  
Working Fluid ◽  
Two Phase ◽  
Fluidelastic Instability

An experimental study was conducted to investigate damping and fluidelastic instability in tube arrays subjected to two-phase cross-flow. The purpose of this research was to improve our understanding of these phenomena and how they are affected by void fraction and flow regime. The working fluid used was Freon 11, which better models steam-water than air-water mixtures in terms of vapour-liquid mass ratio as well as permitting phase changes due to pressure fluctuations. The damping measurements were obtained by “plucking” the monitored tube from outside the test section using electromagnets. An exponential function was fitted to the tube decay trace, producing consistent damping measurements and minimizing the effect of frequency shifting due to fluid added mass fluctuations. The void fraction was measured using a gamma densitometer, introducing an improvement over the Homogeneous Equilibrium Model (HEM) in terms of density and velocity predictions. It was found that the Capillary number, when combined with the two-phase damping ratio (interfacial damping), shows a well defined behaviour depending on the flow regime. This observation can be used to develop a better methodology to normalize damping results. The fluidelastic results agree with previously presented data when analyzed using the HEM and the half-power bandwidth method. The interfacial velocity is suggested for fluidelastic studies due to its capability for collapsing the fluidelastic data. The interfacial damping was introduced as a tool to include the effects of flow regime into the stability maps.

Investigation of In-Flow Fluidelastic Instability of Square Tube Arrays Subjected to Air Cross Flow

2015 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Shinichiro Hagiwara ◽  
Joji Yamada ◽  
Kenji Usuki
Keyword(s):  
Nuclear Power ◽  
Flow Instability ◽  
Flow Direction ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Nuclear Industry ◽  
Flexible Cylinder ◽  
Triangular Arrays ◽  
Tube Arrays ◽  
Fluidelastic Instability

In-flow instability of tube arrays is a recent major issue in heat exchanger design since the event at a nuclear power plant in California [1]. In our previous tests [2], the effect of the pitch-to-diameter ratio on fluidelastic instability in triangular arrays is reported. This is one of the present major issues in the nuclear industry. However, tube arrays in some heat exchangers are arranged as a square array configuration. Then, it is important to study the in-flow instability on the case of square arrays. The in-flow fluidelastic instability of square arrays is investigated in this report. It was easy to observe the in-flow instability of triangular arrays, but not for square arrays. The pitch-to-diameter ratio, P/D, is changed from 1.2 to 1.5. In-flow fluidelastic instability was not observed in the in-flow direction. Contrarily, the transverse instability is observed in all cases including the case of a single flexible cylinder. The test results are finally reported including the comparison with the triangular arrays.

Measurement of Flow-Induced Forces: A Single Flexible Tube in a Rigid Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow

2015 ◽  
Author(s):  
Enrico Deri ◽  
Joël Nibas ◽  
Olivier Ries ◽  
André Adobes
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Tube Bundle ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Maintenance Policy ◽  
Excitation Spectra ◽  
Two Phase ◽  
Force Coefficients ◽  
Out Of Plane

Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators of nuclear power plants. In order to predict damages due to such vibrations, EDF has developed the numerical tool GeViBus, which allows one to asses risk and thereafter to optimize the SG maintenance policy. The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be assessed by experiment. The database of dimensionless coefficients is updated in order to cover all existing tube bundle configurations. Within this framework, a new test rig was presented in a previous conference with the aim of assessing parallel triangular tube arrangement submitted to a two-phase cross-flow. This paper presents the result of the first phase of the associated experiments in terms of force coefficients and two-phase flow excitation spectra for both in-plane and out-of-plane vibration.

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