On modeling fluidelastic instability in tube arrays subjected to two-phase cross-flow

2019 ◽  
Vol 90 ◽  
pp. 1-18 ◽  
Author(s):  
J.E. Moran ◽  
D.S. Weaver
Keyword(s):  
Cross Flow ◽  
Two Phase ◽  
Tube Arrays ◽  
Fluidelastic Instability

Streamwise Fluidelastic Instability of Tube Arrays in Two-Phase Cross Flow

2014 ◽  
Author(s):  
Stephen Olala ◽  
Njuki W. Mureithi
Keyword(s):  
Nuclear Power ◽  
Single Phase ◽  
Cross Flow ◽  
Force Measurements ◽  
Two Phase Flows ◽  
Two Phase ◽  
Fluid Force ◽  
Void Fractions ◽  
Tube Arrays ◽  
Fluidelastic Instability

In-plane instability of tube arrays has not been a major concern to steam generator designers until recently following observations of streamwise tube failure in a nuclear power plant in U.S.A. However, modeling of fluidelastic instability in two-phase flows still remains a challenge. In the present work, detailed steady fluid force measurements for a kernel of an array of tubes in a rotated triangular tube array of P/D=1.5 subjected to air-water two-phase flows for a series of void fractions and a Reynolds number (based on the pitch velocity), Re = 7.2 × 104 has been conducted. The measured steady fluid force coefficients and their derivatives, with respect to streamwise static displacements of the central tube, are employed in the quasi-steady model [1, 2], originally developed for single phase flows, to analyze in-plane fluidelastic instability of multiple flexible arrays in two-phase flows. The results are consistent with dynamic stability tests [3].

Prediction of Streamwise Fluidelastic Instability of a Tube Array in Two-Phase Flow and Effect of Frequency Detuning

2016 ◽  
Vol 139 (3) ◽  
Author(s):  
Stephen Olala ◽  
Njuki W. Mureithi
Keyword(s):  
Cross Flow ◽  
Instability Threshold ◽  
Plane Boundary ◽  
Contact Friction ◽  
Frequency Detuning ◽  
Two Phase ◽  
Void Fractions ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
The Stability

Experimental measurements of the steady forces on a central cluster of tubes in a rotated triangular array (P/D=1.5) subjected to two-phase air–water cross-flow have been conducted. The tests were done for a series of void fractions and a Reynolds number (based on the pitch velocity), Re=7.2×104. The forces obtained and their derivatives with respect to the static streamwise displacement of the central tube in the cluster were then used to perform a quasi-steady fluidelastic instability analysis. The predicted instability velocities were found to be in good agreement with the dynamic stability tests. Since the effect of the time delay was ignored, the analysis confirmed the predominance of the stiffness-controlled mechanism in causing streamwise fluidelastic instability. The effect of frequency detuning on the streamwise fluidelastic instability threshold was also explored. It was found that frequency detuning has, in general, a stabilizing effect. However, for a large initial variance in a population of frequencies (e.g., σ2=7.84), a smaller sample drawn from the larger population may have lower or higher variance resulting in a large scatter in possible values of the stability constant, K, some even lower than the average (tuned) case. Frequency detuning clearly has important implications for streamwise fluidelastic instability in the steam generator U-bend region where in-plane boundary conditions, due to preload and contact friction variance, are poorly defined. The present analysis has, in particular, demonstrated the potential of the quasi-steady model in predicting streamwise fluidelastic instability threshold in tube arrays subjected to two-phase cross-flows.

Implementation of Machine Learning Algorithms for Prediction of Fluidelastic Instability in Tube Arrays

2021 ◽  
Vol 143 (2) ◽  
Author(s):  
Joaquin E. Moran ◽  
Yasser Selima
Keyword(s):  
Machine Learning ◽  
Logistic Regression ◽  
Learning Algorithm ◽  
Machine Learning Algorithms ◽  
Two Phase ◽  
Factors Affecting ◽  
Logistic Regression Models ◽  
Number Of Factors ◽  
Tube Arrays ◽  
Fluidelastic Instability

Abstract Fluidelastic instability (FEI) in tube arrays has been studied extensively experimentally and theoretically for the last 50 years, due to its potential to cause significant damage in short periods. Incidents similar to those observed at San Onofre Nuclear Generating Station indicate that the problem is not yet fully understood, probably due to the large number of factors affecting the phenomenon. In this study, a new approach for the analysis and interpretation of FEI data using machine learning (ML) algorithms is explored. FEI data for both single and two-phase flows have been collected from the literature and utilized for training a machine learning algorithm in order to either provide estimates of the reduced velocity (single and two-phase) or indicate if the bundle is stable or unstable under certain conditions (two-phase). The analysis included the use of logistic regression as a classification algorithm for two-phase flow problems to determine if specific conditions produce a stable or unstable response. The results of this study provide some insight into the capability and potential of logistic regression models to analyze FEI if appropriate quantities of experimental data are available.

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.

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

Vibration of a Tube Bundle in Two-Phase Freon Cross-Flow

1995 ◽  
Vol 117 (4) ◽  
pp. 321-329 ◽  
Author(s):  
M. J. Pettigrew ◽  
C. E. Taylor ◽  
J. H. Jong ◽  
I. G. Currie
Keyword(s):  
Two Phase Flow ◽  
Tube Bundle ◽  
Density Ratio ◽  
Cross Flow ◽  
Flow Regimes ◽  
Phase Flow ◽  
Two Phase ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
First Results

Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.

Investigations of In-Plane Fluidelastic Instability in a Multi-Span U-Bend Tube Bundle: Tests in Air Flow

2017 ◽  
Author(s):  
Paul Feenstra ◽  
Teguewinde Sawadogo ◽  
Bruce Smith ◽  
Victor Janzen ◽  
Helen Cothron
Keyword(s):  
Steam Generator ◽  
Tube Bundle ◽  
Air Flow ◽  
Cross Flow ◽  
Test Rig ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Fluidelastic Instability ◽  
Air Blower ◽  
R 134A

The tubes in the U-bend region of a recirculating type of nuclear steam generator are subjected to cross-flow of a two-phase mixture of steam and water. There is a concern that these tubes may experience flow-induced vibration, including the damaging effects of fluidelastic instability. This paper presents an update and results from a series of flow-induced vibration experiments performed by Canadian Nuclear Laboratories for the Electric Power Research Institute (EPRI) using the Multi-Span U-Bend test rig. In the present experiments, the main focus was to investigate fluidelastic instability of the U-tubes subjected to a cross-flow of air. The tube bundle is made of 22 U-tubes of 0.5 in (12.7 mm) diameter, arranged in a rotated triangular configuration with a pitch-over-diameter ratio of 1.5. The test rig could be equipped with variable clearance flat bar supports at two different locations to investigate a variety of tube and support configurations. The primary purpose of the overall project is to study the effect of flat bar supports on ‘in plane’ (‘streamwise’) instability in a U-tube bundle with realistic tube-to-support clearances or preloads, and eventually in two-phase flow conditions. Initially, the test rig was designed for tests in air-flow using an industrial air blower. Tests with two-phase Freon refrigerant (R-134a) will follow. This paper describes the test rig, experimental setup, and the challenges presented by simulating an accurate representation of current steam generator designs. Results from the first series of tests in air flow are described.

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