Modal Analysis of a Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow

2017 ◽  
Author(s):  
Enrico Deri
Keyword(s):  
Modal Analysis ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Nuclear Industry ◽  
Mode Shapes ◽  
Physical Analysis ◽  
Maintenance Policy ◽  
Two Phase ◽  
Safety Margins ◽  
Lift And Drag

Flow-induced vibrations of tubes in two-phase heat exchangers are a concern for the nuclear industry. EDF has developed a numerical tool, which allows one to evaluate safety margins and thereafter to optimize the exchanger maintenance policy. The software is based on a semi analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be evaluated by experiment. A test rig was presented in previous PVP conferences with the aim of assessing parallel triangular tube arrangement submitted to a two-phase vertical cross-flow: a kernel of nine flexible tubes is set in the middle of a rigid bundle. These tubes vibrate as solid bodies (in translation) both in the lift and drag directions. This paper presents some extended physical analysis applied to some selected points of the aforementioned experiment series: the response modes are identified by means of operational modal analysis (i.e. under unmeasured flow excitation) and presented in terms of frequency, damping and mode shapes. Among all the modes theoretically possible in the bundle, it was found that some of them have a higher response depending on the flow velocity and the void fraction. Mode shapes allow to argue if lock-in is present and to clarify the role of lift and drag forces close to the fluidelastic instability.

Operational Modal Analysis of a Triangular-Pitch Tube Bundle Subjected to Two-Phase Cross-Flow

2018 ◽  
Vol 140 (3) ◽  
Author(s):  
Enrico Deri
Keyword(s):  
Modal Analysis ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Nuclear Industry ◽  
Operational Modal Analysis ◽  
Mode Shapes ◽  
Physical Analysis ◽  
Two Phase ◽  
Safety Margins ◽  
Lift And Drag

Flow-induced vibrations of tubes in two-phase heat exchangers are a concern for the nuclear industry. Electricité de France (EDF) has developed a numerical tool, which allows one to evaluate safety margins and thereafter to optimize the exchanger maintenance policy. The software is based on a semi-analytical model of fluid-dynamic forces and dimensionless fluid force coefficients which need to be evaluated by experiment. A test rig was operated with the aim of assessing parallel triangular tube arrangement submitted to a two-phase vertical cross-flow: a kernel of nine flexible tubes is set in the middle of a rigid bundle. These tubes vibrate as solid bodies (in translation) both in the lift and drag directions in order to represent the so-called in-plane and out-of-plane vibrations. This paper outlines the experimental results and some detailed physical analysis of some selected points of the experiment series: the response modes are identified by means of operational modal analysis (OMA) (i.e., under unmeasured flow excitation) and presented in terms of frequency, damping, and mode shapes. Among all the modes theoretically possible in the bundle, it was found that some of them have a higher response depending on the flow velocity and the void fraction. Mode shapes allow to argue if lock-in is present and to clarify the role of lift and drag forces close to the fluid-elastic instability (FEI).

Measurement of Flow-Induced Forces: Multiple Flexible Tubes in a Triangular-Pitch Bundle Subjected to Two-Phase Cross-Flow

2016 ◽  
Author(s):  
Enrico Deri ◽  
Olivier Ries ◽  
André Adobes
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Tube Bundle ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Maintenance Policy ◽  
Excitation Spectra ◽  
Two Phase ◽  
Safety Margins ◽  
Flexible Tubes

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 evaluate safety margins 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 progressively updated in order to cover most of 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 fluid-induced forces measured on a set of flexible tubes placed in a triangular pitch bundle both in the lift and drag directions. Two-phase flow excitation spectra are presented as well.

A New Test-Bench for Studying Vibrations of Tubes in Parallel Triangular Bundles Under Two-Phase Cross-Flow

2014 ◽  
Author(s):  
Enrico Deri ◽  
Joël Nibas ◽  
André Adobes
Keyword(s):  
Nuclear Power ◽  
Power Plants ◽  
Tube Bundle ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Maintenance Policy ◽  
Test Rig ◽  
Two Phase ◽  
Safety Margins ◽  
Test Loop

Flow-induced vibrations of Steam Generator (SG) 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 evaluate safety margins 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 steadily updated in order to cover all tube bundle configurations found in EDF power plants. Within this framework, we present a new test rig dedicated to the parallel triangular tube arrangement submitted to a two-phase cross-flow. A new test loop is constructed as well, allowing fluid-elastic instability to be induced on the test rig for various qualities. The details of the experimental arrangement are presented together with the preliminary validation tests.

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.

Vibration Excitation Forces in a Normal Triangular Tube Bundle Subjected to Two-Phase Cross Flow

2011 ◽  
Author(s):  
E. S. Perrot ◽  
N. W. Mureithi ◽  
M. J. Pettigrew ◽  
G. Ricciardi
Keyword(s):  
Tube Bundle ◽  
Cross Flow ◽  
Random Excitation ◽  
Two Phase ◽  
Constant Frequency ◽  
Fluid Forces ◽  
Drag Forces ◽  
Wide Range ◽  
Drag And Lift ◽  
Lift And Drag

This paper presents test results of vibration forces in a normal triangular tube bundle subjected to air-water cross-flow. The dynamic lift and drag forces were measured with strain gage instrumented cylinders. The array has a pitch-to-diameter ratio of 1.5, and the tube diameter is 38 mm. A wide range of void fraction and fluid velocities were tested. The experiments revealed significant forces in both the drag and lift directions. Constant frequency and quasi-periodic fluid forces were found in addition to random excitation. These forces were analyzed and characterized to understand their origins. The forces were found to be dependent on the position of the cylinder within the bundle. The results are compared with those obtained with flexible cylinders in the same tube bundle and to those for a rotated triangular tube bundle. These comparisons reveal the influence of quasi-periodic forces on tube motions.

Study on the Fluidelastic Vibration of Tube Arrays Using Modal Analysis Technique

1984 ◽  
Vol 106 (1) ◽  
pp. 17-24 ◽  
Author(s):  
K. Ohta ◽  
K. Kagawa ◽  
H. Tanaka ◽  
S. Takahara
Keyword(s):  
Modal Analysis ◽  
Heat Exchangers ◽  
Vibration Mode ◽  
Fluid Dynamic ◽  
Cross Flow ◽  
Dynamic Force ◽  
Reversed Flow ◽  
Critical Flow Velocity ◽  
Analysis Technique ◽  
Tube Arrays

This paper presents a method to calculate the critical flow velocity of fluidelastic vibration of tube arrays in heat exchangers. The method is based upon the modal analysis technique, which combines the fluid dynamic force caused by cross flow and the vibration characteristics of the complicated tube array to obtain its response. The analytical method enables us not only to take into account the vibration mode of tube array and nonuniformity of velocity and density distribution of cross flow, but also to estimate the effect of antivibration devices, such as spacer, connecting band, and so on. Numerical examples of constrained single-tube array, multi-tube array in reversed flow, and group of panels with spacers are described.

Primitive Model for the Random Excitation of a Tube Under Two-Phase Cross Flow

2016 ◽  
Author(s):  
Laurent Borsoi ◽  
Philippe Piteau ◽  
Xavier Delaune ◽  
Jose Antunes
Keyword(s):  
Two Phase Flow ◽  
Tube Bundle ◽  
Cross Flow ◽  
Interface Velocity ◽  
Momentum Conservation ◽  
Random Excitation ◽  
Nuclear Industry ◽  
Phase Flow ◽  
Two Phase ◽  
Primitive Model

Flow-induced vibration of heat-exchangers tubes is particularly studied in the nuclear industry for safety and cost reasons. It implies to have, among others, relevant characterizations of the random buffeting forces the cross-flow applies to the tube bundle. Work is still needed in this domain, particularly for two-phase flow, to improve the available data as the ones for PWR steam generator, currently very envelope. In parallel to get new experimental data, using “real” or substitutional mixtures (e.g. air-water instead of steam-water for PWR), it is essential to understand the basic excitation mechanisms which induce the vibrations under two-phase flow, as e.g. the influence of flow regimes. In this general framework, what can be learnt from deliberately simple models may be a contributive help. As a first attempt on this issue, the paper deals with the elementary case of a single rigid tube under air-water cross flow. This case is part of experiments carried out at CEA-Saclay with bundles where both tube support reactions and flow characteristics are measured, with respectively piezo-electrical sensors and bi-optical probes (BOP). The information provided by the BOP (mean interface velocity, statistical distribution, etc.) feeds a primitive model of water “droplet” impulses on the tube, based on a lot of crude assumptions about impact velocity, momentum conservation, impulse shape, statistical independence, etc., and which uses analytical results of random processes constructed from the superposition of random pulses. The “equivalent” excitation force, obtained in terms of dimensional PSD, is compared to the one measured in the drag and lift direction with an acceptable agreement, at least in order of magnitude. Comments and lessons are drawn from this first attempt, and some paths are advanced to improve this kind of primitive models, especially for treating rigid square bundles under air-water cross flow.

Vibration Response Characteristics of Tandem Two Circular Cylinders Subjected to a Two-Phase Cross Flow—Effects of Pitch-to-Diameter Ratio

1992 ◽  
Vol 114 (4) ◽  
pp. 444-452 ◽  
Author(s):  
F. Hara ◽  
T. Iijima ◽  
T. Nojima
Keyword(s):  
Void Fraction ◽  
Vibration Suppression ◽  
Cross Flow ◽  
Diameter Ratio ◽  
Circular Cylinders ◽  
Air Bubbles ◽  
Two Phase ◽  
Response Characteristics ◽  
Small Pitch ◽  
Lift And Drag

This paper deals experimentally with the comparison of air bubble effects on the vibration of two circular cylinders installed in tandem at pitch-to-diameter ratios of 1.5 and 3.0. Experiments were done for both the pitch-to-diameter ratios changing the void fraction from 0 to about 20 percent for the reduced velocity ranging from 0.5 to 8; vibrational accelerations were measured in both the lift and drag directions for each cylinder and the results were compared with for each other between the pitch-to-diameter ratios of 1.5 and 3. The comparison revealed that 1) the vibration of the tandem two-cylinder system having a pitch-to-diameter ratio of 1.5 or 3 was excited by air bubbles in the flow for small reduced velocity, but the effect of pitch-to-diameter ratio was found in the response characteristics of the upstream cylinder’s vibration in the lift direction; 2) a small amount of air bubbles equivalent to about 4 percent of the void fraction suppressed the strong, out-of-phase vibration in the downstream cylinder of a large P/D of 3 when the reduced velocity was about 7, but the cylinder arrangement with a small pitch-to-diameter ratio of 1.5 showed a weaker vibration reduction due to adding air bubbles in the flow at high flow velocity; and 3) the vibration suppression was likely due to the entrainment of air bubbles in the wake region behind the upstream cylinder.

Influence of the Pitch-to-Diameter Ratio on Two-Phase Flow-Induced Forces Across a Tube Bundle

2019 ◽  
Author(s):  
Enrico Deri
Keyword(s):  
Power Plants ◽  
Two Phase Flow ◽  
Tube Bundle ◽  
Fluid Dynamic ◽  
Diameter Ratio ◽  
Analytical Models ◽  
Phase Flow ◽  
Excitation Spectra ◽  
Two Phase ◽  
Safety Margins

Abstract Flow-induced vibrations of Steam Generator tube bundles are a major concern for the operators and designers of nuclear power plants. In order to predict damages due to such vibrations, predictive calculations are performed, both by designers and by operators, which allow one to evaluate safety margins and thereafter to optimize the SG maintenance policy. In cases when semi analytical models of fluid-dynamic forces are used, together with corresponding dimensionless fluid force coefficients, closures are assessed by experiment. The database of dimensionless coefficients should then cover relevant tube bundle configurations. Within this framework, a test rig which was available at EDF was modified in order to arrange different pitch-to-diameter ratio bundles and different tube diameters. This paper discusses the fluid-induced forces measured on a set of flexible tubes placed in a triangular pitch bundle both in the lift and drag directions. Two-phase flow excitation spectra are presented as well.

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