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.

Experimental Investigation on Vortex Shedding and Fluid Elastic Instability in Finned Tube Arrays Subjected to Water Cross Flow

2017 ◽  
Vol 139 (5) ◽  
Author(s):  
Sandeep R. Desai ◽  
S. Pavitran
Keyword(s):  
Vortex Shedding ◽  
Water Flow Rate ◽  
Cross Flow ◽  
Elastic Vibration ◽  
Finned Tube ◽  
Elastic Instability ◽  
Process Industries ◽  
Hydrodynamic Coupling ◽  
Test Parameters ◽  
Tube Arrays

The paper presents results of an experimental study on fluid elastic instability and vortex shedding in plain and finned arrays exposed to water cross flow. The parallel triangular array with cantilever end condition is considered for the study. Pitch ratios considered are 2.1 and 2.6 while fin densities considered are 4 fpi (fins per inch) and 10 fpi. The results for critical velocity at instability for two finned tube arrays are presented. Apart from results on fluid elastic vibration behavior, extensive results on vortex shedding are also presented to study the phenomenon in tube arrays subjected to water cross flow. The test parameters measured are water flow rate, natural frequency, and vibration amplitudes of the tubes. The datum case results were first obtained by testing plain arrays with pitch ratios 2.1 and 2.6. This was then followed by experiments with finned arrays with pitch ratios 2.1 and 2.6, and each with two different fin densities. The higher pitch ratios typical of chemical process industries resulted in the delayed instability threshold due to weak hydrodynamic coupling between the neighboring tubes. The results indicated that finned arrays are more stable in water cross flow compared to plain arrays. The Strouhal numbers corresponding to small peaks observed before fluid elastic instability are computed and compared with the expected ones according to Owen's hypothesis. It was concluded that peaks observed are attributed to vortex shedding observed for all the arrays tested in water.

Numerical Simulation of Vortex Shedding Past a Circular Cylinder in a Cross-Flow at Low Reynolds Number With Finite Volume-Technique: Part 1 — Forced Oscillations

2007 ◽  
Author(s):  
Antoine Placzek ◽  
Jean-Franc¸ois Sigrist ◽  
Aziz Hamdouni
Keyword(s):  
Numerical Simulation ◽  
Reynolds Number ◽  
Circular Cylinder ◽  
Finite Volume ◽  
Vortex Shedding ◽  
Stokes Equations ◽  
Cross Flow ◽  
Forced Oscillations ◽  
Lift And Drag ◽  
Wake Characteristics

The numerical simulation of the flow past a circular cylinder forced to oscillate transversely to the incident stream is presented here for a fixed Reynolds number equal to 100. The 2D Navier-Stokes equations are solved with a classical Finite Volume Method with an industrial CFD code which has been coupled with a user subroutine to obtain an explicit staggered procedure providing the cylinder displacement. A preliminary work is conducted in order to check the computation of the wake characteristics for Reynolds numbers smaller than 150. The Strouhal frequency fS, the lift and drag coefficients CL and CD are thus controlled among other parameters. The simulations are then performed with forced oscillations f0 for different frequency rations F = f0/fS in [0.50–1.50] and an amplitude A varying between 0.25 and 1.25. The wake characteristics are analysed using the time series of the fluctuating aerodynamic coefficients and their FFT. The frequency content is then linked to the shape of the phase portrait and to the vortex shedding mode. By choosing interesting couples (A,F), different vortex shedding modes have been observed, which are similar to those of the Williamson-Roshko map.

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.

Vortex-Shedding Response of Long Cylindrical Structures in Shear Flow

1988 ◽  
Vol 110 (1) ◽  
pp. 24-31 ◽  
Author(s):  
E. Wang ◽  
A. K. Whitney ◽  
K. G. Nikkel
Keyword(s):  
Shear Flow ◽  
Vortex Shedding ◽  
Solution Method ◽  
Lift Coefficient ◽  
Cross Flow ◽  
Quantitative Agreement ◽  
Cylindrical Structures ◽  
Fluid Damping ◽  
Energy Dissipated ◽  
Random Vibration Analysis

The response of cylindrical structures to vortex shedding in a vertically sheared cross flow is analyzed. In contrast to the uniform cross-flow case, shear flow can excite more than one modal frequency at a time. Thus, the net response of the structure is a superposition of several vibration modes. The amplitude of each mode is determined by a balance between energy fed into the structure over a “locked-on” region of the structure and energy dissipated by fluid damping over the remainder of the structure. A solution method based on random vibration analysis is developed that uses an empirically derived lift coefficient and correlation length models. The technique is capable of handling both uniform and sheared (depth-varying) current profiles. Good quantitative agreement is found between the present method and the very limited field data available for shear flows, although it is concluded that the shear conditions in the tests were not sufficiently strong to validate the theory conclusively. The results show how using uniform-flow approximations to treat shear flow cases can significantly overpredict vibration amplitudes caused by vortex shedding.

Fluidelastic Vibration of Heat Exchanger Tube Arrays

1978 ◽  
Vol 100 (2) ◽  
pp. 347-353 ◽  
Author(s):  
H. J. Connors
Keyword(s):  
Heat Exchanger ◽  
Flow Velocity ◽  
Cross Flow ◽  
Test Results ◽  
Excitation Mechanism ◽  
Heat Exchanger Tube ◽  
Flow Test ◽  
Tube Arrays ◽  
Instability Constant ◽  
Exchanger Tube

A basic fluidelastic excitation mechanism, of a type reported in an earlier paper, causes large whirling vibrations of tubes in model arrays when the flow velocity exceeds a critical value. The critical velocity is U = βfnDmoδn/ρoD2 where β, the threshold instability constant is a function of the tube pattern and spacing. Threshold instability constants are given that were obtained from wind tunnel and water tunnel tests on multirow tube arrays in uniform cross flow. Test results are discussed that demonstrate the effects of spanwise variations in flow velocity on fluidelastic whirling for both straight tubes and U-tubes. Design methods are provided for predicting the onset of fluidelastic whirling of heat exchanger tubes on multiple supports when spanwise variations in the cross flow exist.

Multimode Fluid Elastic Instability of Heat Exchanger Tubes

2013 ◽  
Vol 136 (1) ◽  
Author(s):  
R. D. Blevins
Keyword(s):  
Stability Analysis ◽  
Heat Exchanger ◽  
Flow Velocity ◽  
Natural Frequencies ◽  
Cross Flow ◽  
Elastic Instability ◽  
Nonuniform Flow ◽  
Instability Analysis ◽  
The Stability

Multimode fluid elastic instability analysis is made of heat exchanger tubes in cross flow. The stability analysis predicts that the flow velocity for onset of tube instability in nonuniform flow is lowered by participation of multiple tube modes with similar natural frequencies.

Numerical Simulation of the Flow-Sound Interaction Mechanisms of a Single and Two-Tandem Cylinders in Cross-Flow

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
A. Mohany ◽  
S. Ziada
Keyword(s):  
Numerical Simulation ◽  
Flow Field ◽  
Flow Velocity ◽  
Vortex Shedding ◽  
Cross Flow ◽  
Acoustic Resonance ◽  
Positive Energy ◽  
Single Cylinder ◽  
Interaction Mechanisms ◽  
Tandem Cylinders

A numerical simulation of the flow-excited acoustic resonance for the case of two-tandem cylinders in cross-flow is performed. The spacing ratio between the cylinders (L/D=2.5) is inside the proximity interference region. Similar simulation is performed for the case of a single cylinder. The unsteady flow field is simulated using a finite-volume method. This simulation is then coupled with a finite-element simulation of the resonant sound field, by means of Howe’s theory of aerodynamics sound, to reveal the details of flow-sound interaction mechanisms, including the nature and the locations of the aeroacoustic sources in the flow field. For the case of a single cylinder, acoustic resonance is excited over a single range of flow velocity. The main aeroacoustic source, which causes a positive energy transfer from the flow field to the acoustic field, is found to be located just downstream of the cylinder. For the case of two-tandem cylinders, the acoustic resonance is excited over two different ranges of flow velocity: the precoincidence and the coincidence resonance ranges. For the coincidence resonance range, the main aeroacoustic source is found to be located just downstream of the downstream cylinder, and the excitation mechanism of this resonance range is found to be similar to that of a single cylinder. However, for the precoincidence resonance range, the primary acoustic source is found to be located in the gap between the cylinders. Moreover, flow visualization of the wake structure for the two-tandem cylinders during acoustic resonance shows that for the precoincidence resonance range there is a phase shift of about 90 deg between the vortex shedding from the upstream and the downstream cylinders, which is different from the coincidence resonance range, where the vortex shedding from both cylinders seems to be in-phase.

Sign in / Sign up

Export Citation Format

Share Document