The Effects of Tube Array Geometry on Fluidelastic Instability in Heat Exchanger Tube Arrays in Cross Flow

2017 ◽  
Author(s):  
Marwan Hassan ◽  
David S. Weaver
Keyword(s):  
Experimental Data ◽  
Research Effort ◽  
Cross Flow ◽  
Triangular Arrays ◽  
Small Pitch ◽  
Fluidelastic Instability ◽  
Significant Research ◽  
Current Design ◽  
Pitch Ratio ◽  
Array Geometry

The shut-down of the San Onofre Nuclear Generating Station (SONGS) has been attributed to damaging streamwise Fluidelastic Instability (FEI) of the steam generator tubes, a phenomenon which has traditionally been assumed not to occur. This has generated a significant research effort to better understand this phenomenon and to develop appropriate design criteria for its prevention. Most current design codes are based on Connors criterion for FEI which neglects both streamwise FEI and the effects of tube array pattern and pitch ratio. It is becoming clear that array geometry and pitch ratio are important determining factors in FEI, especially in the streamwise direction. This paper presents an extension of the theory of Lever and Weaver to consider arrays of flexible fluid-coupled tubes which are free to become unstable in both the transverse and streamwise directions. This simplified modelling approach has the advantages of being very tractable for numerical parametric studies and having no need for experimental data input. Previous research by the authors has shown that the predictions of this model agree very well with the available experiments for parallel triangular arrays for both transverse and streamwise FEI. In this paper, the results of such studies are presented for the both transverse and streamwise FEI for square inline and normal triangular arrays and compared with the authors’ previous results for parallel triangular arrays. It is shown that FEI is strongly influenced by array geometry, especially for small pitch ratio arrays operating at low values of the mass damping parameter. The results show good agreement with the available experimental data.

Estimation of the Time Delay Associated With Damping Controlled Fluidelastic Instability in a Normal Triangular Tube Array

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Time Delay ◽  
Cross Flow ◽  
Fluid Forces ◽  
Fluidelastic Instability ◽  
Order Of Magnitude ◽  
Sample Frequency ◽  
Pitch Ratio ◽  
Parameterized Model ◽  
Semi Empirical ◽  
Insight Into

Fluidelastic instability (FEI) produces large amplitude self-excited vibrations close to the natural frequency of the structure. For fluidelastic instability caused by the damping controlled mechanism, there is a time delay between tube motion and the resulting fluid forces but magnitude and physical cause of this is unclear. This study measures the time delay between tube motion and the resulting fluid forces in a normal triangular tube array with a pitch ratio of 1.32 subject to air cross-flow. The instrumented cylinder was forced to oscillate in the lift direction at three excitation frequencies for a range of flow velocities. Unsteady surface pressures were monitored with a sample frequency of 2 kHz at the mid plane of the instrumented cylinder. The instantaneous fluid forces were obtained by integrating the surface pressure data. A time delay between the tube motion and resulting fluid forces was obtained. The nondimensionalized time delay was of the same order of magnitude assumed in the semi-empirical quasi-steady model (i.e., τ2 = 0.29 d/U). Although, further work is required to provide a parameterized model of the time delay which can be embedded in a model of damping controlled fluidelastic forces, the data already provides some insight into the physical mechanism responsible.

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.

A Semipotential Flow Theory for the Dynamics of Cylinder Arrays in Cross Flow

1985 ◽  
Vol 107 (4) ◽  
pp. 500-506 ◽  
Author(s):  
M. P. Paidoussis ◽  
S. J. Price ◽  
D. Mavriplis
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Fluid Dynamic ◽  
Dynamic Stiffness ◽  
Cross Flow ◽  
Flow Region ◽  
High Mass ◽  
Duct Flow ◽  
Cylinder Arrays ◽  
Fluidelastic Instability

This paper presents a semianalytical model, involving the superposition of the empirically determined cross flow about a cylinder in an array and the analytically determined vibration-induced flow field in still fluid, for the purpose of analyzing the stability of cylinder arrays in cross flow and predicting the threshold of fluidelastic instability. The flow field is divided into two regions: a viscous bubble of separated flow, and an inviscid, sinuous duct-flow region elsewhere. The only empirical input required by the model in its simplest form is the pressure distribution about a cylinder in the array. The results obtained are in reasonably good accord with experimental data, only for low values of the mass-damping parameter (e.g., for liquid flows), where fluidelastic instability is predominantly caused by negative fluid-dynamic damping terms. For high mass-damping parameters (e.g., for gaseous flows), where fluidelastic instability is evidently controlled by fluid-dynamic stiffness terms, the model greatly overestimates the threshold of fluidelastic instability. However, once measured fluid-dynamic stiffness terms are included in the model, agreement with experimental data is much improved, yielding the threshold flow velocities for fluidelastic instability to within a factor of 2 or better.

An Investigation on the Use of Connors’ Equation to Predict Fluidelastic Instability in Cylinder Arrays

2001 ◽  
Vol 123 (4) ◽  
pp. 448-453 ◽  
Author(s):  
Stuart J. Price
Keyword(s):  
Experimental Data ◽  
Cross Flow ◽  
Theoretical Models ◽  
Implicit Assumption ◽  
Cylinder Arrays ◽  
Fluidelastic Instability

The use of Connors’ equation, or variations thereof, to predict the velocity at which fluidelastic instability occurs in cylinder arrays subject to cross-flow has become ubiquitous. The implicit assumption being that this equation accurately models the physics of fluidelastic instability, and all that is required is to find the “correct” value of Connors’ constant. The evidence for and against this assumption is examined in this paper. Other theoretical models of fluidelastic instability are reviewed and compared with Connors’ analysis. In addition, evidence from experimental data is considered. It is concluded that there are many deficiencies associated with Connors’ equation, and that if better “design guides” are to be obtained, more emphasis must be put on examining the physics of fluidelastic instability.

Study on the Stream-Wise Fluidelastic Instability of Rotated Square Arrays of Circular Cylinders Subjected on Cross-Flow

2017 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Tomoki Tsujita
Keyword(s):  
Nuclear Power ◽  
Cross Flow ◽  
Critical Factor ◽  
Circular Cylinders ◽  
Test Facility ◽  
Test Results ◽  
Steam Generators ◽  
Triangular Arrays ◽  
Specific Direction ◽  
Fluidelastic Instability

Stream-wise fluidelastic instability has recently been in the spotlight due to a practical event in steam generators at a nuclear power plant [1]. The instability has been reported to occur easily in rotated triangular arrays, but at all hardly in normal triangular arrays [2][3]. In square arrays, no instability has been reported in the authors’ test facility [4]. This paper presents the test results on rotated square arrays of the pitch-diameter ratios from 1.2 to 1.5. The tests have been conducted with a wind tunnel, where cylinders have been constrained to move in only one specific direction, either stream-wise or transverse to the flow. The results indicate that fluidelastic vibrations occur only in the stream-wise direction. The critical factor corresponds to the previous data reported in some guidelines [5], but here the factor is related mainly to stream-wise instability.

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.

Fluidelastic Vibration Analysis of Normal Square Finned Tube Arrays in Water Cross Flow

2019 ◽  
Vol 141 (3) ◽  
Author(s):  
Sandeep R. Desai ◽  
Aslam A. Maniyar
Keyword(s):  
Vortex Shedding ◽  
Fluid Velocity ◽  
Cross Flow ◽  
Finned Tube ◽  
Instability Threshold ◽  
Experimental Program ◽  
Triangular Arrays ◽  
Array Pattern ◽  
Tube Arrays ◽  
Pitch Ratio

An experimental program was carried out by subjecting normal square finned tube arrays to gradually increasing water cross flows. In all, total six tube arrays were tested—three having pitch ratio 2.1 and remaining three of pitch ratio 2.6. Under each category, three arrays tested were: plain array, coarse finned array, and fine finned array. The objective of the research was to determine the fluid velocity at which each of the six arrays becomes fluidelastically unstable. The experiments were started with tests on plain arrays to establish them as a datum case by comparing their test results with published results on plain arrays having lower pitch ratios. This was then followed by testing of finned arrays to study the effect of fins on the instability threshold. The tubes were subjected to a gradually increasing flow rate of water from 10 m3/h to the point where instability was reached. The results of the present work are compared with author's earlier published results for parallel triangular arrays in water. The research outcomes help to study the effect of pitch ratio, tube array pattern, and fin density on the instability threshold. The results show that instability is delayed due to the addition of the fins. It is also concluded that normal square arrays should be preferred over parallel triangular arrays to avoid fluidelastic vibrations. The vortex shedding behavior studied for all the arrays shows that small peaks before fluidelastic instability are due to vortex shedding.

Towards a Validation Database for Simulation of Fluidelastic Instability in Normal Triangular Heat Exchanger Tube Arrays

2008 ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Surface Pressure ◽  
Cross Flow ◽  
Initial Step ◽  
Pressure Measurements ◽  
Dynamic Head ◽  
Flow Surface ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Large Asymmetry ◽  
Pitch Ratio

Models for fluidelastic instability are usually validated by comparing critical velocity predictions with experimental data. However, the scatter in this data make detailed validation problematic. As an initial step towards providing a validation database for fluidelastic instability, surface pressure measurements are presented for a cylinder in the third row of three normal triangular tube arrays (P/d = 1.32; 1.58; 1.97) with air cross flow. Surface pressure measurements were also made when the cylinder was statically displaced. Forces were calculated from the pressure measurements enabling an understanding of the force generation mechanism. The results show that the fluid force coefficients do not scale with the dynamic head but exhibit a dependency on Reynolds number and pitch ratio. However, no simple parametrisation was found for the lift force. Jet switching was found in P/d = 1.58 even when the tube was displaced. This phenomenon resulted in the large asymmetry observed in the pressure distribution around a static cylinder.

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.

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