Study on In-Flow Fluidelastic Instability of Triangular Tube Arrays Subjected to Air Cross Flow

2014 ◽  
Vol 136 (5) ◽  
Author(s):  
Tomomichi Nakamura ◽  
Yoshiaki Fujita ◽  
Takuya Sumitani
Keyword(s):  
Transverse Direction ◽  
Flow Instability ◽  
Flow Direction ◽  
Present Report ◽  
Air Flow ◽  
Cross Flow ◽  
Thin Plates ◽  
Cylinder Arrays ◽  
Cylinder Array ◽  
Fluidelastic Instability

The in-flow instability of cylinder arrays corresponds to the in-plane instability of U-bend tubes in steam generators. This rarely occurring phenomenon has recently been observed in a nuclear power plant in the U.S. For this reason, the importance of studying this instability has recently increased. The fluidelastic instability of a cylinder array caused by cross-flow was found to easily occur in air-flow and hardly in water-flow in our previous report. The present report introduces the results of this phenomenon in several patterns of triangular cylinder arrays in air-flow. The pitch spacing between cylinders is one of the parameters, which varies from P/D = 1.2 to 1.5, for a five-by-five cylinder array. The instability is examined both in the in-flow direction and in the transverse direction. The test cylinders are supported with thin plates to move in one direction. The number and the location of the flexibly supported cylinders are the other parameters. Differences between the instability in the in-flow and in the transverse direction are found. Among these differences the most important is the fact that the fluidelastic instability has not been observed for a single flexible cylinder in the in-flow direction, although it is observed in the transverse direction. However, the present preliminary results suggest that the in-flow instability may be estimated with the Connors' type formula as likely as in the transverse direction case.

Study on In-Flow Fluidelastic Instability of Circular Cylinders Caused by Air Cross Flow (Triangular Arrays)

2013 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Yoshiaki Fujita ◽  
Takuya Sumitani ◽  
Shinichiro Hagiwara
Keyword(s):  
Transverse Direction ◽  
Flow Instability ◽  
Flow Direction ◽  
Present Report ◽  
Air Flow ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Cylinder Arrays ◽  
Cylinder Array ◽  
Fluidelastic Instability

The in-flow instability of cylinder arrays corresponds to the in-plane instability of U-bend tubes in steam generators. This rarely occurring phenomenon has recently been observed in a nuclear power plant in U.S.A. For this reason, the importance of studying this instability has recently increased. The fluidelastic instability of a cylinder array caused by cross-flow was found to easily occur in air-flow and hardly in water-flow in our previous report. The present report introduces the results of this phenomenon in several patterns of triangular cylinder arrays in air-flow. The pitch spacing between cylinders is one of the parameters, which varies from P/D = 1.2 to 1.5, for a five-by-five cylinder array. The instability is examined both in the in-flow direction and in the transverse direction. The test cylinders are supported with thin plates to move in one direction. The number and the location of the flexibly supported cylinders are the other parameters. Differences between the instability in the in-flow and in the transverse direction are found. Among these differences the most important is the fact that the fluidelastic instability has not been observed for a single flexible cylinder in the in-flow direction, although it is observed in the transverse direction. However, the in-flow instability can be estimated with the Connors’ type formula as in the transverse direction.

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.

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.

Study on In-Flow Vibration of Cylinder Arrays Caused by Cross Flow

2011 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Keisuke Nishimura ◽  
Yoshiaki Fujita ◽  
Chihiro Kohara
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Thin Plates ◽  
Streamwise Direction ◽  
Number Range ◽  
Direction Transverse ◽  
Drag Forces ◽  
Cylinder Arrays ◽  
Reynolds Number Range

The authors have studied the in-flow vibration phenomena of cylinder arrays caused by cross-flow in the low Reynolds number range around Re=800. This Reynolds number range has been studied because it is the range where symmetric vortex shedding occurs. This report is our first trial to study the in-line fluidelastic vibration of cylinder arrays. In initial tests, the flow velocity was increased up to the maximum achievable level by the test equipment. However, it was found that the array’s cantilever tube supports resulted in large static tube deflections due to static drag forces. The cylinder array tube supports have therefore been replaced by thin plates supported at both ends. The cylinders are set to be flexible both in the streamwise direction and the direction transverse to the flow. The obtained results of these two patterns are also compared with previous cantilevered data. The origin of the observed vibrations whether a self-induced mechanism or vortex shedding is discussed in detail.

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.

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.

A Study on Stream-Wise Oscillation of Cylinder Arrays: Effect of Pitch Ratio

2009 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Takafumi Yoshikawa ◽  
Taku Yoshimura ◽  
Hironobu Kondo
Keyword(s):  
High Speed ◽  
Flow Direction ◽  
Cross Flow ◽  
Video Camera ◽  
Strain Gages ◽  
Flow Oscillation ◽  
Digital Video Camera ◽  
Cylinder Arrays ◽  
Tube Arrays ◽  
Pitch Ratio

The importance of the in-flow oscillation of a single cylinder in cross-flow has been spotlighted since an accident in a FBR-type reactor. However, the in-flow oscillation can be observed in tube arrays of heat exchangers. Previous reports show some interesting phenomena on the oscillation of cylinder arrays, which have a same pitch between cylinders. This paper shows the effect of the pitch ratio of a cylinder array on the characteristics of those phenomena, especially in in-flow direction, where every cylinder can move only in this direction. The motion of cylinders is measured by attached strain gages and by a high-speed digital video camera.

Investigation on In-Flow Fluidelastic Instability of an Array of Tubes

2013 ◽  
Author(s):  
Kazuo Hirota ◽  
Hideyuki Morita ◽  
Jun Hirai ◽  
Akihisa Iwasaki ◽  
Seiho Utsumi ◽  
...  
Keyword(s):  
Flow Velocity ◽  
Flow Direction ◽  
Cross Flow ◽  
Critical Flow ◽  
Steam Generators ◽  
Critical Flow Velocity ◽  
Fluidelastic Instability ◽  
Vibration Mechanism ◽  
The Cross ◽  
The Relationship

Fluidelastic instability (FEI) remains the most important vibration mechanism in steam generators. Fluidelastic instability of an array of tubes thought to be mainly occurred in the cross-flow direction. In the present day, some researchers reported possibility of occurrence of fluidelastic instability in the in-flow direction. However, the phenomenon of the in-plane FEI has not been well recognized compared to the transverse FEI. In this study, air flow tests using cantilevered straight cylinder array of tubes in triangular configuration were conducted. It is confirmed that the in-flow FEI could be occurred and the critical flow velocity in the in-flow direction is larger than that of in the cross flow direction. Furthermore, the relationship between P/D of an array of tubes and the critical flow velocity in the in-flow direction was also investigated.

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