An Investigation Into the Post-Stable Behavior of a Tube Array in Cross-Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 457-465
Author(s):  
J. H. Lever ◽  
G. Rzentkowski
Keyword(s):  
Flow Velocity ◽  
Cross Flow ◽  
Elastic Stability ◽  
Critical Flow Velocity ◽  
Tube Arrays ◽  
Pitch Ratio ◽  
Velocity Increments ◽  
The Subject ◽  
Flexible Tubes

In the experimental determination of fluid-elastic stability thresholds in tube arrays, the critical flow velocity is normally approached from below. Once large amplitude whirling motions are initiated, however, the system often does not retrace the response curve as flow velocity is reduced. This hysteresis behavior has been the subject of a recent investigation utilizing a newly constructed wind tunnel facility at Memorial University. The post-stable response of a 1.375-pitch ratio parallel triangular array was first generated under steady flow conditions, with positive velocity increments to just beyond the threshold, then velocity reductions in steps back to stable amplitude levels. It was found that an array with 7 central flexible tubes displayed a fairly broad hysteresis loop, while the same array with only a single flexible tube displayed no hysteresis. The transition from steady stable response levels to steady unstable response levels was then investigated using two types of transient excitation: tube displacement and flow velocity. The effect of increasing tube damping was also investigated.

Determination of the Fluid-Elastic Stability Threshold in the Presence of Turbulence: A Theoretical Study

1989 ◽  
Vol 111 (4) ◽  
pp. 407-419 ◽  
Author(s):  
J. H. Lever ◽  
G. Rzentkowski
Keyword(s):  
Theoretical Study ◽  
Cross Flow ◽  
Elastic Stability ◽  
Mass Ratio ◽  
Response Curves ◽  
Stability Threshold ◽  
Pitch Ratio ◽  
The Stability ◽  
Experimental Findings

A model has been developed to examine the effect of the superposition of turbulent buffeting and fluid-elastic excitation on the response of a single flexible tube in an array exposed to cross-flow. The modeled response curves for a 1.375-pitch ratio parallel triangular array are compared with corresponding experimental data for the same array; reasonably good qualitative agreement is seen. Turbulence is shown to have a significant effect on the determination of the stability threshold for the array, with increasing turbulent buffeting causing a reduction in the apparent critical velocity. The dependence of turbulence response on mass ratio is also found to yield a slight independence between mass and damping parameters on stability threshold estimates, which may account for similar experimental findings. Different stability criteria are compared, and an attempt is made to provide some guidance in the interpretation of response curves from actual tests.

Some Issues Concerning Fluid-Elastic Instability of a Group of Circular Cylinders in Cross-Flow

1989 ◽  
Vol 111 (4) ◽  
pp. 507-518 ◽  
Author(s):  
S. S. Chen
Keyword(s):  
Flow Velocity ◽  
State Of The Art ◽  
Cross Flow ◽  
Circular Cylinders ◽  
Critical Flow ◽  
Elastic Instability ◽  
Stability Criteria ◽  
Critical Flow Velocity ◽  
Current State

Since the early 1970s, extensive studies of fluid-elastic instability of circular cylinders in cross-flow have been reported. A significant understanding of the phenomena involved now exists. However, some confusion, misunderstanding, and misinterpretation still remain. The objective of this paper is to discuss, based on the current state of the art, a series of the most asked questions. Emphasis is placed on the determination of the critical flow velocity, nondimensional parameters, stability criteria, and instability mechanisms.

An Analysis of In-Flow Fluidelastic Instability Based on a Physical Insight

2014 ◽  
Author(s):  
Tomomichi Nakamura
Keyword(s):  
Flow Velocity ◽  
Flow Instability ◽  
Pressure Sensors ◽  
Measured Data ◽  
Critical Flow ◽  
Nonlinear Phenomenon ◽  
Critical Flow Velocity ◽  
Fluid Force ◽  
Tube Arrays ◽  
Fluidelastic Instability

Fluidelastic vibration of tube arrays caused by cross-flow has recently been highlighted by a practical event. There have been many studies on fluidelastic instability, but almost all works have been devoted to the tube-vibration in the transverse direction to the flow. For this reason, there are few data on the fluidelastic forces for the in-flow movement of the tubes, although the measured data on the stability boundary has gradually increased. The most popular method to estimate the fluidelastic force is to measure the force acting on tubes due to the flow, combined with the movement of the tubes. However, this method does not give the physical explanation of the root-cause of fluidelastic instability. In the work reported here, the in-flow instability is assumed to be a nonlinear phenomenon with a retarded or delayed action between adjacent tubes. The fluid force acting on tubes are estimated, based on the measured data in another paper for the fixed cylinders with distributed pressure sensors on the surface of the cylinders. The fluid force acting on the downstream-cylinder is assumed in this paper to have a delayed time basically based on the distance between the separation point of the upstream-cylinder to the re-attachment point, where the fluid flows with a certain flow velocity. Two models are considered: a two-cylinder and three–cylinder models, based on the same dimensions as our experimental data to check the critical flow velocity. Both models show the same order of the critical flow velocity and a similar trend for the effect of the pitch-to-diameter ratio of the tube arrays, which indicates this analysis has a potential to explain the in-flow instability if an adequate fluid force is used.

Spanwise Correlation of Surface Pressure Fluctuations in Heat Exchanger Tube Arrays

2010 ◽  
Author(s):  
John Mahon ◽  
Paul Cheeran ◽  
Craig Meskell
Keyword(s):  
Heat Exchanger ◽  
Surface Pressure ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Fretting Wear ◽  
Heat Exchanger Tube ◽  
Tube Arrays ◽  
Pitch Ratio ◽  
Excitation Mechanisms ◽  
Exchanger Tube

An experimental study of the surface spanwise pressure on a cylinder in the third row of two normal triangular tube arrays (P/d = 1.32 and 1.58) with air cross flow has been conducted. A range of flow velocities were examined. The correlation of surface pressure fluctuations due to various vibration excitation mechanisms along the span of heat exchanger tubes has been assessed. The turbulent buffeting is found to be uncorrelated along the span which is consistent with generally accepted assumptions in previous studies. Vortex shedding and acoustic resonances were well correlated along the span of the cylinder, with correlations lengths approaching the entire length of the cylinder. Jet switching was observed in the pitch ratio of 1.58 and was found to be correlated along the cylinder, although the spatial behaviour is complex. This result suggests that the excitation force used in fretting wear models may need to be updated to include jet switching in the calculation.

Flow Velocity Dependence of Damping in Tube Arrays Subjected to Liquid Cross-Flow

1981 ◽  
Vol 103 (2) ◽  
pp. 130-135 ◽  
Author(s):  
S. S. Chen ◽  
J. A. Jendrzejczyk
Keyword(s):  
Mathematical Modeling ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Elastic Instability ◽  
Velocity Dependence ◽  
Tube Arrays ◽  
Fluid Damping ◽  
Lift And Drag

Experiments are conducted to determine the damping for a tube in tube arrays subjected to liquid cross-flow; damping factors in the lift and drag directions are measured for in-line and staggered arrays. It is found that: 1) fluid damping is not a constant, but a function of flow velocity; 2) damping factors in the lift and drag directions are different; 3) fluid damping depends on the tube location in an array; 4) flow velocity-dependent damping is coupled with vortex shedding process and fluid-elastic instability; and 5) flow velocity-dependent damping may be negative. This study demonstrates that flow velocity-dependent damping is important. These characteristics should be properly taken into account in the mathematical modeling of tube arrays subjected to cross-flow.

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.

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.

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.

Fluid-Elastic Instability of Normal Square Tube Bundles in Two-Phase Cross Flow

2010 ◽  
Author(s):  
Woo Gun Sim ◽  
Mi Yeon Park
Keyword(s):  
Heat Exchanger ◽  
Flow Velocity ◽  
Dynamic Instability ◽  
Cross Flow ◽  
Elastic Instability ◽  
Two Phase ◽  
Critical Flow Velocity ◽  
Tube Heat Exchanger ◽  
Tube Bundles ◽  
Square Array

Some knowledge on damping and fluid-elastic instability is necessary to avoid flow-induced-vibration problems in shell and tube heat exchanger such as steam generator. Fluid-elastic instability is the most important vibration excitation mechanism for heat exchanger tube bundles subjected to the cross flow. Experiments have been performed to investigate fluid-elastic instability of normal square tube bundles, subjected to two-phase cross flow. The test section consists of cantilevered flexible cylinder(s) and rigid cylinders of normal square array. From a practical design point of view, fluid-elastic instability may be expressed simply in terms of dimensionless flow velocity and dimensionless mass-damping parameter. For dynamic instability of cylinder rows, added mass, damping and critical flow velocity are evaluated. The Fluid-elastic instability coefficient is calculated and then compared to existing results given for tube bundles in normal square array.

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.

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