Investigation of Natural Frequency and Damping Ratio Due to Flow-Induced Vibration in a Finned Tube Subjected to Cross-Flow

2021 ◽  
Vol 15 (3) ◽  
pp. 133
Author(s):  
Pravin Hindurao Yadav ◽  
Dillip Kumar Mohanty
Keyword(s):  
Natural Frequency ◽  
Damping Ratio ◽  
Cross Flow ◽  
Finned Tube ◽  
Flow Induced Vibration

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.

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.

Experimental analysis of fluid elastic vibrations in rotated square finned tube arrays subjected to water cross flow

2019 ◽  
Vol 233 (17) ◽  
pp. 6124-6134 ◽  
Author(s):  
Sandeep R Desai ◽  
Rohit V Kengar
Keyword(s):  
Research Work ◽  
Cross Flow ◽  
Finned Tube ◽  
Fretting Wear ◽  
Flow Induced Vibration ◽  
Tube Heat Exchanger ◽  
Finned Tubes ◽  
Array Pattern ◽  
Tube Arrays ◽  
Plain Tube

The majority of the failures of shell and tube heat exchanger tubes are reported due to the flow-induced vibration caused by shell side cross flow. Fluid elastic instability, vortex shedding, and turbulent buffeting are the excitation mechanisms responsible for the failure of the tubes. The failure occurs due to tube-to-tube impacts leading to impaction marks on the tube surface and, subsequently, leading to the failure due to fretting wear and fatigue. The present research work deals with the determination of critical velocity at instability for rotated square finned tube arrays subjected to water cross flow. In all, total six tube arrays are tested with two different pitch ratios, each with a plain tube array, a coarse finned tube array, and a fine finned tube array. Pitch ratios considered in the study are 2.1 and 2.6, while fin densities considered are coarse (4 fpi = 6.35 mm) and fine (10 fpi = 2.54 mm). The effect of array pattern, pitch ratio, and fin density on the onset of instability is studied by conducting experiments in the water cross flow. The effect of tube array pattern is studied by comparing the results of the present study with authors' published results for parallel triangular finned tube arrays in the water cross flow. The study led to the conclusion that the instability threshold is delayed for rotated square tube arrays compared to parallel triangular tube arrays. It is also observed that instability thresholds for coarse and fine finned tubes are delayed compared to plain tubes and is found to be more for finned tubes with higher fin densities.

Vibration of Tube Bundles in Two-Phase Cross-Flow: Part 1—Hydrodynamic Mass and Damping

1989 ◽  
Vol 111 (4) ◽  
pp. 466-477 ◽  
Author(s):  
M. J. Pettigrew ◽  
C. E. Taylor ◽  
B. S. Kim
Keyword(s):  
Tube Bundle ◽  
Damping Ratio ◽  
Cross Flow ◽  
Design Guidelines ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Mixture Density ◽  
Void Fractions ◽  
Mass Fluxes ◽  
Tube Bundles

Two-phase cross-flow exists in many shell-and-tube heat exchangers, such as condensers, reboilers and nuclear steam generators. An understanding of damping and of flow-induced vibration excitation mechanisms is necessary to avoid problems due to excessive tube vibration. Accordingly, we have undertaken an extensive program to study the vibration behavior of tube bundles subjected to two-phase cross-flow. In this paper we present the results of experiments on four tube bundle configurations; namely, normal triangular of pitch over diameter ratio, p/d, of 1.32 and 1.47, and parallel triangular and normal square of p/d of 1.47. The bundles were subjected to air-water mixtures to simulate realistic mass fluxes and vapor qualities corresponding to void fractions from 5 to 99 percent. Hydrodynamic mass and damping are discussed in Part 1 of this series of three papers. We found that hydrodynamic mass is roughly related to the homogeneous mixture density. The damping characteristics of all tube bundles are generally similar. Damping is maximum between 40 and 80 percent void fraction where the damping ratio reaches about 4 percent. The effect of mass flux is generally weak. Design guidelines are proposed for hydrodynamic mass and for damping.

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.

DESIGN OF AN FINNED TUBE EVAPORATOR WITH CROSS-FLOW FOR A REFRIGERATION MACHINE OPERATING WITH CO2 IN SUBCRYTIC CYCLE

2017 ◽  
Author(s):  
Carlos Henrique Neto da silva ◽  
Hélio Augusto Goulart Diniz ◽  
Ivo Zatti Lima Meyer ◽  
Grack Rodrigues Gama ◽  
Leandro Pinto
Keyword(s):  
Cross Flow ◽  
Finned Tube ◽  
Refrigeration Machine

Vortex-Induced Vibrations of a Cylinder at Subcritical Reynolds Number

2011 ◽  
Author(s):  
Yoann Jus ◽  
Elisabeth Longatte ◽  
Jean-Camille Chassaing ◽  
Pierre Sagaut
Keyword(s):  
Reynolds Number ◽  
Numerical Simulations ◽  
Numerical Study ◽  
Damping Ratio ◽  
Experimental Studies ◽  
Cross Flow ◽  
Physical Analysis ◽  
Arbitrary Lagrangian Eulerian ◽  
Vortex Induced Vibrations ◽  
Low Mass

The present work focusses on the numerical study of Vortex-Induced Vibrations (VIV) of an elastically mounted cylinder in a cross flow at moderate Reynolds numbers. Low mass-damping experimental studies show that the dynamic behavior of the cylinder exhibits a three-branch response model, depending on the range of the reduced velocity. However, few numerical simulations deal with accurate computations of the VIV amplitudes at the lock-in upper branch of the bifurcation diagram. In this work, the dynamic response of the cylinder is investigated by means of three-dimensional Large Eddy Simulation (LES). An Arbitrary Lagrangian Eulerian framework is employed to account for fluid solid interface boundary motion and grid deformation. Numerous numerical simulations are performed at a Reynolds number of 3900 for both no damping and low-mass damping ratio and various reduced velocities. A detailed physical analysis is conducted to show how the present methodology is able to capture the different VIV responses.

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.

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.

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