Fluid Elastic Whirling of a Tube Row

1974 ◽  
Vol 96 (4) ◽  
pp. 263-267 ◽  
Author(s):  
R. D. Blevins
Keyword(s):  
Natural Frequency ◽  
Analytical Model ◽  
Heat Exchangers ◽  
Free Stream ◽  
Cross Flow ◽  
Flow Induced Vibration ◽  
Adjacent Wall

An analytical model for flow-induced vibration of a tube row in a cross flow is formulated. A criterion for the onset of instability is developed. The tubes are modeled with different stiffnesses and damping normal and parallel to the free stream to simulate effects which arise in heat exchangers. The critical reduced velocity required for the onset of instability is shown to increase sharply with the separation of natural frequency between tubes. The effect of an adjacent wall and rows composed of a small number of tubes is explored. The model reduces to an experimentally validated criterion for symmetrically supported tubes.

Prevention and Cure of Flow-Induced Vibration Problems in Tubular Heat Exchangers

1980 ◽  
Vol 102 (2) ◽  
pp. 138-145 ◽  
Author(s):  
F. L. Eisinger
Keyword(s):  
Heat Exchangers ◽  
Cross Flow ◽  
Acoustic Vibration ◽  
New Method ◽  
Flow Induced Vibration ◽  
Tube Bank ◽  
Vibration Resistance ◽  
Stability Diagrams ◽  
Vibration Problems ◽  
Prevention And Cure

Various methods for predicting and solving tube and acoustic vibration problems in heat exchangers in cross flow are presented: the use of stability diagrams comprising in-service experience of heat exchangers, for a general multispan tube model; a method of selecting efficient baffle configurations for prevention of acoustic vibration, a new method of fin barriers, an alternative to conventional baffling; a new method of enhancing the vibration resistance of a tube bank based on the use of a helical spacer; these methods, singly or in combination, can be used to design against flow-induced vibration.

Effect of Upstream Cylinder’s Oscillation Frequency on Downstream Cylinder’s Vortex Induced Vibration

2016 ◽  
Author(s):  
M. Mobassher Tofa ◽  
Adi Maimun ◽  
Yasser M. Ahmed
Keyword(s):  
Natural Frequency ◽  
Oscillation Frequency ◽  
Flow Direction ◽  
Cross Flow ◽  
Clean Energy ◽  
Mass Ratio ◽  
Flow Induced Vibration ◽  
Tandem Arrangement ◽  
Vortex Induced Vibration ◽  
Single Cylinder

Vortex induced vibration or widely known as VIV, is a very complex hydrodynamic phenomenon. There are relatively very few experimental and numerical references for oscillating pair of cylinders because of the early assumption that the interference between the two cylinders is weak and thus each of the cylinders may have the same behavior as found in the case of a single cylinder, but recent researches showed this assumption was not true. For tandem arrangement, several parameters govern the nature of VIV of downstream cylinders, such as spacing, upstream cylinders VIV amplitude etc. The nature of downstream cylinders response isn’t same as classical VIV or WIV (wake induced vibration). Oscillation frequency of a cylinder subjected to flow induced vibration is one of the important characteristics Oscillation frequency is highly dependent on natural frequency of the cylinder. By changing spring stiffness or mass ratio, natural frequency can be altered. The aim of this study is to investigate the effect of upstream cylinder’s oscillation frequency on the vibration of downstream cylinder. Numerical simulations have been conducted to understand the nature of vortex induced vibration (VIV) of a pair cylinder in tandem arrangement at high Reynolds numbers. Cylinders were subjected to uniform flows in sub-critical flow regime and have been allowed to oscillate in cross flow direction only. The spacing between the upstream and downstream cylinders was four times of the cylinder diameter. The oscillation frequency of the upstream cylinder has been altered by varying the mass ratio of the upstream cylinder. It was found that for same Reynolds number, downstream cylinder’s VIV amplitude is increased quite significantly if the upstream cylinder oscillates relatively slowly. The shear stress transport detached eddy turbulence model has been used for simulating the turbulent flow around the two cylinders. An advanced mesh movement known as “mesh morphing” model was employed to lessen the requirement for re-meshing which help to increase the accuracy of the prediction. Calculation of accurate results due to large domain deformations was achieved by re-positioning existing mesh points. The numerical results of a single cylinder subjected to one degree of freedom (1DOF) vibration have been compared with the available experimental results to validate the present study. The study is important in terms of designing VIVACE (Vortex Induced Vibration for Aquatic Clean Energy) converter for low speed current. In recent past, multiple cylinders have been used for VIVACE converter. So, the study of VIV of two equal-diameter cylinders in tandem arrangement at low current speed is very significant.

Flow-Induced Vibration of a Cylinder in the Wake of Another of Smaller Diameter

2014 ◽  
Author(s):  
Md. Mahbub Alam ◽  
An Ran ◽  
Yu Zhou
Keyword(s):  
Circular Cylinder ◽  
Free Stream ◽  
Cross Flow ◽  
Induced Response ◽  
Stream Velocity ◽  
Flow Induced Vibration ◽  
Cylinder Diameter ◽  
Spacing Ratio ◽  
Vortex Shedding Frequency ◽  
Shedding Frequency

This paper presents cross-flow induced response of a both-end-spring-mounted circular cylinder (diameter D) placed in the wake of a rigid circular cylinder of smaller diameter d. The cylinder vibration is constrained to the transverse direction. The cylinder diameter ratio d/D and spacing ratio L/d are varied from 0.2 to 1.0 and 1.0 to 5.5, respectively, where L is the distance between the center of the upstream cylinder to the forward stagnation point of the downstream cylinder. A violent vibration of the cylinder is observed for d/D = 0.2 ∼ 0.8 at L/d = 1.0, for d/D = 0.24 ∼ 0.6 at 1.0 < L/d ≤ 2.5, for d/D = 0.2 ∼ 0.4 at 2.5 < L/d ≤ 3.5, and for d/D = 0.2 at 3.5 < L/d ≤ 5.5, but not for d/D = 1.0. A smaller d/D generates vibration for a longer range of L/d. The violent vibration occurs at a reduced velocity Ur (=U∞/fnD, where U∞ is the free-stream velocity and fn the natural frequency of the cylinder system) beyond the vortex excitation regime (Ur ≥ 8) depending on d/D and L/d. Once the vibration starts to occur, the vibration amplitude increases rapidly with increasing Ur. It is further noted that the flow behind the downstream cylinder is characterized by two predominant frequencies, corresponding to the cylinder vibration frequency and the natural vortex shedding frequency of the cylinder, respectively. While the former persists downstream, the latter vanishes rapidly.

Solving the Flow Induced Vibration Problem in Desuperheating Zones of Feedwater Heaters by Using No-Tube-in-the-Window (NTIW) Baffling

2009 ◽  
Author(s):  
Thomas J. Muldoon
Keyword(s):  
Natural Frequency ◽  
Safety Margin ◽  
Cross Flow ◽  
Thermal Design ◽  
Distinct Advantage ◽  
Mean Flow ◽  
Flow Induced Vibration ◽  
Pressure Drops ◽  
Overall Design ◽  
The Mean

Feedwater heaters have suffered premature failures in the desuperheating zone resulting from a combination of high cross flow velocities and relatively long baffle spacing. High steam flows coupled with longer unsupported tube spans necessary to keep pressure drops low and tube walls dry create an increased probability for flow induced vibration. This vibration is primarily the result of a fluidelastic whirling of the tube. The most significant factor in the calculation of the natural frequency of the tube is unsupported span length. The natural frequency varies as the square of the unsupported span. Keeping the span short is critical in avoiding flow induced vibration. No-Tubes-in-the-Window (NTIW) baffling allows the use of intermediate support plates without affecting the mean flow velocity in the baffle space. This allows the thermal design engineer the distinct advantage of providing a design with a very high safety margin at any anticipated overload condition. The asymmetrical flow pattern necessitated by the U-tube design of high pressure feedwater heaters can be appropriately modeled to yield an overall design heat transfer coefficient.

Prediction of Flow-Induced Vibrations in Tubular Heat Exchangers—Part II: Experimental Investigation

2008 ◽  
Vol 131 (1) ◽  
Author(s):  
S. A. Al-Kaabi ◽  
Y. A. Khulief ◽  
S. A. Said
Keyword(s):  
Heat Exchangers ◽  
Complex Dynamics ◽  
Cross Flow ◽  
Analytical Models ◽  
Test Rig ◽  
Flow Induced Vibration ◽  
Tube Arrays ◽  
Tube Bundles ◽  
Flow Induced Vibrations ◽  
The Mathematical Model

It has become evident that the modeling of the complex dynamics of fluidelastic forces that give rise to vibrations of tube bundles requires a great deal of experimental insight. Accordingly, the prediction of the flow-induced vibration due to unsteady cross-flow can be greatly aided by semi-analytical models, in which some coefficients are determined experimentally. A laboratory test rig with an instrumented test bundle is constructed to measure the fluidelastic coefficients to be used in conjunction with the mathematical model derived in Part I of this paper. The test rig admits two different test bundles, namely, the inline-square and 45deg rotated-square tube arrays. Measurements were conducted to identify the flow-induced dynamic coefficients. The developed scheme was utilized in predicting the onset of flow-induced vibrations in two configurations of tube bundles, and results were examined in the light of Tubular Exchange Manufacturers Association (TEMA) predictions. The comparison demonstrated that TEMA guidelines are more conservative in the two configurations considered.

An Experimental Investigation of the Dynamics of a Loosely Supported Tube Array

2017 ◽  
Author(s):  
Amro Elhelaly ◽  
Marwan Hassan ◽  
Atef Mohany ◽  
Soha Moussa
Keyword(s):  
Experimental Investigation ◽  
Impact Force ◽  
Cross Flow ◽  
Open Loop ◽  
Diameter Ratio ◽  
Force Level ◽  
Steam Generators ◽  
Flow Induced Vibration ◽  
System Integrity ◽  
Tube Bundles

The integrity of tube bundles is very important especially when dealing with high-risk applications such as nuclear steam generators. A major issue to system integrity is the flow-induced vibration (FIV). FIV is manifested through several mechanisms including the most severe mechanism; fluidelastic instability (FEI). Tube vibration can be constrained by using tube supports. However, clearances between the tube and their support are required to allow for thermal expansion and for other manufacturing considerations. The clearance between tubes may allow frequent impact and friction between tube and support. This in turn may cause fatigue and wear at support and potential for catastrophic tube failure. This study aims to investigate the dynamics of loosely supported tube array subjected to cross-flow. The work is performed experimentally in an open-loop wind tunnel to address this issue. A loosely-supported single flexible tube in both triangle and square arrays subjected to cross-flow with a pitch-to-diameter ratio of 1.5 and 1.733, respectively were considered. The effect of the flow approach angle, as well as the support clearance on the tube response, are investigated. In addition, the parameters that affect tube wear such as impact force level are presented.

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