Pitch and Pattern Effects on Streamwise Fluidelastic Instability in Tube Arrays

2019 ◽  
Author(s):  
Marwan Hassan ◽  
David Weaver
Keyword(s):  
Los Angeles ◽  
Channel Model ◽  
High Mass ◽  
Flow Induced Vibration ◽  
Geometric Patterns ◽  
Small Pitch ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Pitch Ratio ◽  
The Stability

Abstract Fluidelastic instability (FEI) is well known to be a critical flow-induced vibration concern for the integrity of the tubes in nuclear steam generators. Traditionally, this has been assumed to occur in the direction transverse to the direction of flow but the tube failures at San Onofre Nuclear Generating Station (SONGS) in Los Angeles proved that this assumption is not generally valid. A simple tube-in-channel theoretical model was previously developed to predict streamwise as well as transverse FEI in a parallel triangular tube array. This predicted that this array geometry was particularly sensitive to streamwise FEI for high mass-damping parameters and small pitch ratios, the conditions in which the SONGS failures occurred. The advantage of this simple modelling approach is that no new empirical data are required for parametric studies of the effects of tube pattern and pitch ratio on FEI. The tube-in-channel model has been extended to in-line square, normal triangular and rotated square tube arrays and the stability of these geometric patterns are analyzed for the effects of varying pitch ratio and the mass-damping parameter. The results are compared with the available experimental data and conclusions are drawn regarding the relative vulnerability of these different tube array geometries to streamwise FEI.

Pitch and Pattern Effects On Streamwise Fluidelastic Instability in Tube Arrays

2021 ◽  
Author(s):  
Marwan A. Hassan ◽  
David S. Weaver
Keyword(s):  
Los Angeles ◽  
Channel Model ◽  
High Mass ◽  
Flow Induced Vibration ◽  
Geometric Patterns ◽  
Small Pitch ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Pitch Ratio ◽  
The Stability

Abstract Fluidelastic instability (FEI) is well known to be a critical flow-induced vibration concern for the integrity of the tubes in nuclear steam generators. Traditionally, this has been assumed to occur in the direction transverse to the direction of flow but the tube failures at San Onofre Nuclear Generating Station (SONGS) in Los Angeles proved that this assumption is not generally valid. A simple tube-in-channel theoretical model was previously developed to predict streamwise as well as transverse FEI in a parallel triangular tube array. This predicted that this array geometry was particularly sensitive to streamwise FEI for high mass-damping parameters and small pitch ratios, the conditions in which the SONGS failures occurred. The advantage of this simple modelling approach is that no new empirical data are required for parametric studies of the effects of tube pattern and pitch ratio on FEI. The tube-in-channel model has been extended to in-line square, normal triangular and rotated square tube arrays and the stability of these geometric patterns are analyzed for the effects of varying pitch ratio and the mass-damping parameter. The results are compared with the available experimental data and conclusions are drawn regarding the relative vulnerability of these different tube array geometries to streamwise FEI.

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.

Two-Phase Flow-Induced Vibration of Parallel Triangular Tube Arrays With Asymmetric Support Stiffness

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Paul Feenstra ◽  
David S. Weaver ◽  
Tomomichi Nakamura
Keyword(s):  
Two Phase Flow ◽  
Cross Flow ◽  
Phase Flow ◽  
Heat Exchanger Tube ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Tube Arrays ◽  
Tube Bundles ◽  
Pitch Ratio ◽  
Exchanger Tube

Laboratory experiments were conducted to determine the flow-induced vibration response and fluidelastic instability threshold of model heat exchanger tube bundles subjected to a cross-flow of refrigerant 11. Tube bundles were specially built with tubes cantilever-mounted on rectangular brass support bars so that the stiffness in the streamwise direction was about double that in the transverse direction. This was designed to simulate the tube dynamics in the U-bend region of a recirculating-type nuclear steam generator. Three model tube bundles were studied, one with a pitch ratio of 1.49 and two with a smaller pitch ratio of 1.33. The primary intent of the research was to improve our understanding of the flow-induced vibrations of heat exchanger tube arrays subjected to two-phase cross-flow. Of particular concern was to compare the effect of the asymmetric stiffness on the fluidelastic stability threshold with that of axisymmetric stiffness arrays tested most prominently in literature. The experimental results are analyzed and compared with existing data from literature using various definitions of two-phase fluid parameters. The fluidelastic stability thresholds of the present study agree well with results from previous studies for single-phase flow. In two-phase flow, the comparison of the stability data depends on the definition of two-phase flow velocity.

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

2014 ◽  
Author(s):  
Marwan Hassan ◽  
David S. Weaver
Keyword(s):  
Sliding Friction ◽  
Streamwise Direction ◽  
Flow Induced Vibration ◽  
Direction Parallel ◽  
Short Period ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
The Subject ◽  
Ambient Turbulence

Flow-induced vibration is an important criterion for the design of heat exchangers in nuclear, fossil and chemical plant. 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 anti-vibration bars (AVB) 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.

Analysis of Fluid-Induced Excitation Forces in Triangular Tube Arrays Based on the LES Method

2013 ◽  
Author(s):  
Qing-lei Jiang ◽  
Ji-yun Zhou ◽  
Xian-yuan Wang
Keyword(s):  
Numerical Models ◽  
Random Excitation ◽  
Periodic Excitation ◽  
Frequency Range ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
Small Pitch ◽  
Tube Arrays ◽  
Lift Forces ◽  
Transition Procedure

The turbulence-induced excitation and periodic wake shedding are two important flow-induced vibration mechanisms of tube arrays in steam generators and were normally considered to be random excitation and periodic excitation respectively. Recent findings show that the turbulence-induced excitation is actually the quasi-periodic excitation, which is similar to periodic excitation. Since the turbulence-induced excitation generally occurs in the small pitch-diameter ratio (P/D ratio) tube arrays and the periodic excitation occurs only at large pitch-diameter ratios, the turbulence-induced excitation mechanism seems essentially another form of the periodic excitation at small P/D ratios. To verify this hypothesize and figure out the transition procedure from periodic excitation to quasi-periodic excitation, Numerical simulations were conducted on triangle tube arrays with P/D ratios of 1.47 to 4.0 based on the LES method. Numerical results were compared with experiments results to verify the reliability of numerical models. The lift forces and the force spectra at indifferent P/D ratios were obtained to study the evolution mechanism between turbulence-induced excitation and periodic excitation. The results show that the turbulence-induced excitation and quasi-periodic excitation in tube arrays are essentially other forms of the periodic excitation. The lift forces changed from periodic excitation to quasi-periodic excitation when the P/D ratio was between 2.5 and 3.0, and the lift force nearly complete random excitation when P/D ratios below 1.5. The frequency range of the random excitation is 0 to 50Hz. The peak frequencies of the quasi-periodic excitation were greater than that of periodic excitation and decreased with the increase of P/D ratios.

Partial Admission Effects on the Stability of a Heat Exchanger Tube Array

1988 ◽  
Vol 110 (2) ◽  
pp. 194-198 ◽  
Author(s):  
L. F. Waring ◽  
D. S. Weaver
Keyword(s):  
Heat Exchanger ◽  
Elastic Stability ◽  
Uniform Flow ◽  
Heat Exchanger Tube ◽  
Tube Arrays ◽  
Partial Admission ◽  
Theoretical Predictions ◽  
Pitch Ratio ◽  
The Stability ◽  
Exchanger Tube

An experimental study is reported of the effects of partial admission on the fluid elastic stability of a heat exchanger tube array. The array geometry was a parallel triangular configuration with a pitch ratio of 1.47. Tests were conducted in a wind tunnel with uniform flow over from 33 to 100 percent of single span tubes. In these experiments, the flow location was also varied from center-span to the end supports. Additionally, tests were conducted with uniform flow over one span of two and three-span tube arrays. These results are compared with theoretical predictions.

Fluidelastic Instability of a Single Flexible Tube in a Rigid Tube Array

2010 ◽  
Author(s):  
Ahmed Khalifa ◽  
David Weaver ◽  
Samir Ziada
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Precise Control ◽  
Flexible Tube ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Excitation Mechanisms ◽  
The Stability ◽  
Square Array ◽  
Special Case

Tube and shell heat exchangers are commonly used in both fossil and nuclear power plants. The unexpected failure for such components is expensive and potentially dangerous. Of the various excitation mechanisms which can cause excessive tube vibration, fluidelastic instability is the most dangerous and therefore has received the most attention. The present study reviews the experimental work published in the open literature which involves the use of a single flexible tube in a rigid array to study fluidelastic instability. The data are categorized based on the array geometry into four main groups, parallel triangular, normal triangular, rotated square, and square array patterns. It is concluded from this review that the simplification of using a single flexible tube in a rigid array to study fluidelastic instability should be done with great care, and precise control of some parameters is essential to obtain reliable and repeatable results. Fluidelastic instability of a single flexible tube in a rigid array may occur in some cases, and may be used to improve our understanding of the phenomenon. However, it must be noted that this behavior is a special case and not generally useful for determining the stability of tube arrays.

The Cross-Flow Response of a Tube Array in Water—A Comparison With the Same Array in Air

1982 ◽  
Vol 104 (3) ◽  
pp. 139-146 ◽  
Author(s):  
D. S. Weaver ◽  
D. Koroyannakis
Keyword(s):  
Cross Flow ◽  
Added Mass ◽  
Response Curves ◽  
Flow Response ◽  
Tube Arrays ◽  
Mass Coefficient ◽  
Pitch Ratio ◽  
Added Mass Coefficient ◽  
The Stability ◽  
Wind Tunnel Study

A water tunnel study was conducted on a parallel triangular array of tubes with a pitch ratio of 1.375. The array was geometrically identical to that used previously in a wind tunnel study so that the tube response to cross flow could be compared. It was seen that the response curves for tube arrays in water are much less regular than those in air, creating ambiguity in defining the stability threshold. The irregularities are seen to be associated with shifts in relative tube mode and frequency. Arrays in water apparently first become unstable in one of the lowest frequencies of the band of frequencies associated with a given structural mode. The added mass coefficient computed from the observed frequency at instability is a little larger than the largest added mass coefficient obtained from existing theory for tube arrays in quiescent fluid.

scholarly journals The Effect of Fins on Fluidelastic Instability in In-Line and Rotated Square Tube Arrays

2010 ◽  
Vol 132 (5) ◽  
Author(s):  
Robert H. Lumsden ◽  
David S. Weaver
Keyword(s):  
Finned Tube ◽  
Experimental Program ◽  
Effective Diameter ◽  
Process Industries ◽  
Finned Tubes ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
The Stability ◽  
Tube Pitch ◽  
Bare Tube

An experimental program was conducted to examine fluidelastic instability in in-line and rotated square finned tube arrays. Three arrays of each geometry type were studied: two with serrated, helically wound finned tubes of different fin densities and the third is a bare tube, which had the same base diameter as the finned tubes. The finned tubes under consideration were commercial finned tubes of a type typically used in the fossil and process industries. The addition of fins to tubes in heat exchangers enhances heat transfer due to the increased surface area and the turbulence produced by the flow moving over the fins. The resulting flow pattern/distribution due to the fins is, therefore, more complex than in bare tube arrays. Previous research has shown that an effective diameter of a finned tube is useful in the prediction of vortex shedding. This concept is used to compare the finned tube results with the existing bare tube array guidelines for fluidelastic instability. All of the tube arrays in the present study have the same tube pitch and have been scaled to have the same mass ratio. The results for rotated square arrays suggest that the use of an effective diameter is beneficial in the scaling of fluidelastic instability and the finned tube results are found to fit within the scatter of the existing data for fluidelastic instability. For in-line square arrays, the results indicate that fins significantly increase the stability threshold. An earlier version of this paper appeared at the ASME 2007 PVP Division Conference, PVP2007-26597.

Effect of Tube-to-Tube Ties on Fluidelastic Instability of Tube Arrays Exposed to Crossflow

1998 ◽  
Vol 120 (2) ◽  
pp. 179-185 ◽  
Author(s):  
F. L. Eisinger ◽  
M. M. Rao
Keyword(s):  
Numerical Simulation ◽  
Unsteady Flow ◽  
Flow Theory ◽  
Single Tube ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Critical Velocities ◽  
The Stability ◽  
Stability Limits

Tube-to-tube ties and their arrangement within the tube array are shown to affect the onset of fluidelastic instability. The influence of tie arrangement for a single tube row and for an in-line tube array is obtained by numerical simulation using S. S. Chen’s unsteady flow theory. Maps of dimensionless critical velocities for groups of tubes consisting of two, three, four, and five tubes tied to each other are developed for several design configurations. It is shown that the stability limits can be raised by appropriate choice of tube group and tie location.

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