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RESEARCH PAPERS

Fluidelastic Instability of an Array of Tubes Preferentially Flexible in the Flow Direction Subjected to Two-Phase Cross Flow

[+] Author and Article Information
R. Violette, N. W. Mureithi

BWC/AECL/NSERC Chair of Fluid-Structure Interaction, Department of Mechanical Engineering, École Polytechnique Montréal, QC, Canada, H3C 3A7

M. J. Pettigrew

BWC/AECL/NSERC Chair of Fluid-Structure Interaction, Department of Mechanical Engineering, École Polytechnique Montréal, QC, Canada, H3C 3A7michel.pettigrew@polymtl.ca

J. Pressure Vessel Technol 128(1), 148-159 (Oct 05, 2005) (12 pages) doi:10.1115/1.2138064 History: Received September 02, 2005; Revised October 05, 2005

Almost all the available data about fluidelastic instability of heat exchanger tube bundles concerns tubes that are axisymmetrically flexible. In those cases, the instability is found to be mostly in the direction transverse to the flow. Thus, the direction parallel to the flow has raised less concern in terms of bundle stability. However, the flat bar supports used in steam generator for preventing U-tube vibration may not be as effective in the in-plane direction than in the out-of-plane direction. The possibility that fluidelastic instability can develop in the flow direction must then be assessed. In the present work, tests were done to study the fluidelastic instability of a cluster of seven tubes much more flexible in the flow direction than in the lift direction. The array configuration is rotated triangular with a pitch to diameter ratio of 1.5. The array was subjected to two-phase (air-water) cross flow. Fluidelastic instability was observed when the flexible tubes were located at the center of the test section and also when the seven flexible tubes were placed over two adjacent columns. No instability was found for a single flexible tube in a rigid array, nor for the case where the seven flexible tubes were placed in a single column. Tests were also done with tubes that are axisymmetrically flexible for comparison purposes. It was found that fluidelastic instability occurs at higher velocities when the tubes are flexible only in the flow direction. These results and additional wind tunnel results are compared to existing data on fluidelastic instability. Two-phase flow damping results are also presented in this paper.

Copyright © 2006 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Configurations of flexible tubes tested within the test section

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Figure 2

Flexible tube assembly

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Figure 3

Rms response vs flow pitch velocity for a single tube flexible inflow: —∗—ε=65%, —◆—ε=80%, —∎—ε=90%, —▴—ε=95%

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Figure 4

Response spectra of single tube flexible inflow at 80% void fraction

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Figure 5

Rms response in lift direction vs flow pitch velocity of single tube flexible in all directions: —+—ε=0%, —◇—ε=20%, —◻—ε=40%, —▵—ε=50%, —∗—ε=60%, —◆—ε=80%, —∎—ε=90%

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Figure 6

Rms response of Tube 7 vs flow pitch velocity for the central cluster configuration, 14Hz assembly: —∗—ε=65%, —◆—ε=80%, —∎—ε=90%, —▴—ε=95%

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Figure 7

Rms response of Tube 7 vs flow pitch velocity for the central cluster configuration, 28Hz assembly: —◆—ε=85%, —∎—ε=90%

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Figure 8

Unstable mode of vibration at 80% void fraction for the central cluster configuration, 14Hz tubes flexible inflow: 엯 tubes position at arbitrary time, ∧ tubes movement direction at arbitrary time, + tubes movement limit and equilibrium position

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Figure 9

Rms response in lift direction vs flow pitch velocity for the central cluster configuration, tube flexible in all directions: —+—ε=0% (Tube 7), —◇—ε=20% (Tube 7), —◻—ε=40% (Tube 7), —▵—ε=50% (Tube 7), —∗—ε=60% (Tube 7), —◆—ε=80% (Tube 7), —∎—ε=90% (Tube 7), —▴—ε=95% (Tube 4)

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Figure 10

Orbits of movement of axisymetrically flexible tubes at instability

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Figure 11

Rms response of Tube 7 vs flow pitch velocity for the single flexible column case, tubes flexible inflow: —◆—ε=80%, —∎—ε=90%, —▴—ε=95%

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Figure 12

Rms response of all tubes vs flow pitch velocity at 80% void fraction for the single flexible column case, tubes flexible inflow: —∗— Tube 1, —–— Tube 2, —+— Tube 3, —●— Tube 4, —▴— Tube 5, —∎— Tube 6, —◆— Tube 7

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Figure 13

Tubes dominant vibration frequency vs flow pitch velocity for the single flexible column configuration, tube flexible inflow: —●— Tube 4, —◇— Tube 5, —◻— Tube 6, —●— Tube 7

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Figure 14

Rms response in lift direction vs flow pitch velocity for the single flexible column configuration, tube flexible in all directions: —+—ε=0% (Tube 4), —◇—ε=20% (Tube 4), —◻—ε=40% (Tube 4), —▵—ε=50% (Tube 4), —∗—ε=60% (Tube 4), —◆—ε=80% (Tube 7), —∎—ε=90% (Tube 7), —▴—ε=95% (Tube 7)

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Figure 15

Response spectra in lift direction for a single column flexible in all directions at instability for 50% void fraction

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Figure 16

Rms response of Tube 7 vs flow pitch velocity for the two partially flexible columns case, tubes flexible inflow: —◆—ε=80%, —∎—ε=90%, —▴—ε=95%

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Figure 17

Flow pattern map for two-phase flow across cylinder arrays (Grant (11)) with flow critical conditions: ● tubes flexible inflow (central cluster), ▴ tubes flexible in all direction (central cluster)

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Figure 18

Two-phase flow damping vs flow pitch velocity for the tube flexible inflow, 14Hz tube: —∗—ε=65%, —◆—ε=80%, —∎—ε=90%, —▴—ε=95%

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Figure 19

Two-phase flow damping vs flow pitch velocity for the tube flexible in all directions: —∎— lift direction, —◻— drag direction

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Figure 21

Two-phase flow structure in a rotated triangular tube bundle

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