The Effect of Fin Pitch on Fluid Elastic Instability of Tube Arrays Subjected to Cross Flow of Water

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.

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Analysis for fluid-elastic instability of tube arrays in cross-flow

Mechanical Engineering Journal ◽

10.1299/mej.14-00377 ◽

2015 ◽

Vol 2 (2) ◽

pp. 14-00377-14-00377 ◽

Cited By ~ 1

Author(s):

Masahiko UTSUMI

Keyword(s):

Cross Flow ◽

Elastic Instability ◽

Tube Arrays

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

Journal of Pressure Vessel Technology ◽

10.1115/1.4037263 ◽

2017 ◽

Vol 139 (5) ◽

Cited By ~ 3

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.

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Fluid-elastic instability of in-line tube arrays in cross-flow

Applied Mathematical Modelling ◽

10.1016/0307-904x(90)90184-7 ◽

1990 ◽

Vol 14 (10) ◽

pp. 518-526 ◽

Cited By ~ 3

Author(s):

A. Lowdon ◽

N. Tonks ◽

T.S. Wilkinson

Keyword(s):

Cross Flow ◽

Elastic Instability ◽

Tube Arrays

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Investigation of In-Flow Fluidelastic Instability of Square Tube Arrays Subjected to Air Cross Flow

Volume 4: Fluid-Structure Interaction ◽

10.1115/pvp2015-45091 ◽

2015 ◽

Cited By ~ 1

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.

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