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Research Papers: Fluid-Structure Interaction

Effect of Preferential Flexibility Direction on Fluidelastic Instability of a Rotated Triangular Tube Bundle

[+] Author and Article Information
A. Khalvatti

Department of Mechanical Engineering, BWC/AECL/NSERC Chair of Fluid-Structure Interaction, École Polytechnique, Montréal, QC, H3C 3A7, Canadaafshin.khalvatti@polymtl.ca

N. W. Mureithi

Department of Mechanical Engineering, BWC/AECL/NSERC Chair of Fluid-Structure Interaction, École Polytechnique, Montréal, QC, H3C 3A7, Canadanjuki.mureithi@polymtl.ca

M. J. Pettigrew

Department of Mechanical Engineering, BWC/AECL/NSERC Chair of Fluid-Structure Interaction, École Polytechnique, Montréal, QC, H3C 3A7, CanadaEmail: michel.pettigrew@polymtl.ca

J. Pressure Vessel Technol 132(4), 041309 (Aug 06, 2010) (14 pages) doi:10.1115/1.4002181 History: Received July 06, 2009; Revised June 14, 2010; Published August 06, 2010; Online August 06, 2010

In operating shell-and-tube heat exchangers, tube vibration induced by cross-flow can be a serious problem. The region of concern in steam generators is the upper most U-bend region where the flow crosses a large number of tubes, which also cause significant hydraulic resistance. This hydraulic resistance forces the flow to change direction. From a fluidelastic instability point of view, the tube bundle is excited by oblique cross-flow. A secondary consequence of change in flow direction is a change in the flexibility direction of the tubes relative to the oncoming flow direction at different locations within the U-bend region. It is this somewhat simpler problem that is studied in this work. The effect of array flexibility direction on the fluidelastic instability phenomenon in a rotated-triangular tube bundle is investigated for single phase flow as a starting point. The study consists of both experiments and theoretical analysis of a simplified single-flexible-tube array. Experimental tests are conducted in a wind tunnel on a reconfigurable tube bundle. The results show that fluidelastic instability is strongly dependent on the flexibility angle. The results also show that, generally, the elimination of bundle flexibility in the direction transverse to the flow has a strong stabilizing effect on the tube bundle. The effect is, however, nonlinearly related to flexibility angle. In the second part of this work, the quasi-steady fluidelastic analysis is adapted for a single tube (within a rigid array), flexible in a single but arbitrary direction relative to the flow and subjected to cross-flow. The fluid-force expressions are rewritten to account for an arbitrary tube flexibility direction relative to the approaching flow. In the process, a simplified, flexibility direction dependent, one degree-of-freedom equation is obtained. The model is then evaluated against measured experimental data. This evaluation shows that the predicted critical flow velocity for fluidelastic instability is in qualitative agreement with experimental results, at least in the trend on the effect of varying the flexibility angle. At the same time, the model sheds some light on the role played by the flexibility angle in determining the overall fluid-structure damping underlying the observed stability behavior.

Copyright © 2010 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

(a) Flexible tube assembly and (b) mechanism for setting flexibility orientation.

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Figure 2

Three main tube bundle configurations: (a) fully flexible tube bundle, (b) three-flexible-column tube bundle, and (c) cluster tube bundle

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Figure 3

The four main tube flexibility orientations: (a) 90 deg to flow direction (cross flow), (b) 0 deg to flow direction (in flow direction), (c) 30 deg to flow direction, and (d) 60 deg to flow direction

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Figure 4

RMS vibration response for the fully flexible tube bundle, at a flexibility angle of 90 deg

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Figure 5

(a) Vibration response spectra variation and (b) dominant response frequency for tube 7; plotted versus pitch flow velocity for the flexible tube bundle at a 90 deg flexibility angle

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Figure 6

RMS vibration response for the fully flexible tube bundle, at a flexibility angle 60 deg

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Figure 7

(a) Vibration response spectra variation and (b) dominant response frequency for tube 7 plotted versus pitch flow velocity for the flexible tube bundle at a 60 deg flexibility angle

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Figure 8

RMS vibration response for the fully flexible tube bundle at a flexibility angle 30 deg

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Figure 9

(a) Vibration response spectra variation and (b) dominant response frequency for tube 7; plotted versus pitch flow velocity for the flexible tube bundle at a 30 deg flexibility angle

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Figure 10

RMS vibration response of the fully flexible tube bundle at 0 deg flexibility angle

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Figure 11

Response frequency versus flow pitch velocity for the flexible tube bundle at a 0 deg flexibility angle

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Figure 12

RMS vibration response for the three-column flexible configuration at a 90 deg flexibility angle

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Figure 13

(a) Vibration response spectra variation and (b) dominant response frequency for tube 4; plotted versus pitch flow velocity for the three-flexible-column tube bundle at a 90 deg flexibility angle

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Figure 14

RMS vibration response for the three-column flexible configuration at a 30 deg flexibility angle

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Figure 15

(a) Vibration response spectra variation and (b) dominant response frequency for tube 4; plotted versus pitch flow velocity for the three-flexible-column tube bundle at a 30 deg flexibility angle

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Figure 16

RMS vibration response for the cluster bundle configuration at a 90 deg flexibility angle

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Figure 17

(a) Vibration response spectra variation and (b) dominant response frequency for tube 7; plotted versus pitch flow velocity for the flexible cluster configuration at a 90 deg flexibility angle

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Figure 18

RMS vibration response for the cluster tube bundle configuration at a 60 deg flexibility angle

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Figure 19

(a) Vibration response spectra variation and (b) dominant response frequency for tube 2; plotted versus pitch flow velocity for the flexible cluster configuration at a 60 deg flexibility angle

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Figure 20

RMS vibration response for the fully flexible configuration, tube 7

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Figure 21

RMS vibration response for the three-column flexible configuration, tube 4

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Figure 22

Tests results, pitch velocity as a function of the flexibility angle, and tube bundle configuration

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Figure 23

Cross-section of a small part of an array of tubes in cross flow and coordinate orientation

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Figure 24

Displacement vectors for rotated flexibility angle by θ deg

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Figure 25

Predicted critical upstream velocity variation with flexibility angle compared with experiments

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Figure 26

Upstream velocity variations with flexibility angle for three configurations

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