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Research Papers: Fluid-Structure Interaction

Correlation Between Vibration Excitation Forces and the Dynamic Characteristics of Two-Phase Cross Flow in a Rotated-Triangular Tube Bundle

[+] Author and Article Information
C. Zhang, N. W. Mureithi

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

M. J. Pettigrew

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

J. Pressure Vessel Technol 130(1), 011301 (Jan 08, 2008) (10 pages) doi:10.1115/1.2826381 History: Received July 12, 2006; Revised December 08, 2006; Published January 08, 2008

Two-phase cross flow exists in many shell-and-tube heat exchangers. Flow-induced vibration excitation forces can cause tube motion that will result in long-term fretting wear or fatigue. Detailed flow and vibration excitation force measurements in tube bundles subjected to two-phase cross flow are required to understand the underlying vibration excitation mechanisms. Some of this work has already been done. The distributions of both void fraction and bubble velocity in rotated-triangular tube bundles were obtained. Somewhat unexpected but significant quasiperiodic forces in both the drag and lift directions were measured. The present work aims at understanding the nature of such unexpected drag and lift quasiperiodic forces. An experimental program was undertaken with a rotated-triangular array of cylinders subjected to air/water flow to simulate two-phase mixtures. Fiber-optic probes were developed to measure local void fraction. Both the dynamic lift and drag forces were measured with a strain gage instrumented cylinder. The investigation showed that the quasiperiodic drag and lift forces are generated by different mechanisms that have not been previously observed. The quasiperiodic drag forces appear related to the momentum flux fluctuations in the main flow path between the cylinders. The quasiperiodic lift forces, on the other hand, are mostly correlated to oscillations in the wake of the cylinders. The quasiperiodic lift forces are related to local void fraction measurements in the unsteady wake area between upstream and downstream cylinders. The quasiperiodic drag forces correlate well with similar measurements in the main flow stream between cylinders.

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Copyright © 2008 by American Society of Mechanical Engineers
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Figures

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Figure 2

Idealized two-phase flow signal from fiber-optic probes

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Figure 3

Probe positions for flow measurements

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Figure 7

Power spectra of the local void fraction fluctuation at four different positions on the right side of the main flow path for 80% void fraction at 10m∕s pitch flow velocity; (a) L60deg position, (b) L90deg position, (c) U60deg position, and (d) U90deg position

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Figure 8

Power spectra of the local void fraction fluctuation at four different positions on the left side of the main flow path for 80% void fraction at 5m∕s pitch flow velocity; (a) L60deg position, (b) L90deg position, (c) U60deg position, and (d) U90deg position

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Figure 13

Two-phase flow structure in a rotated-triangular tube bundle: (a) simplified figure (FP, flow path; SZ, stagnation zone), (b) flow picture (1, low void fraction mixture belonging to the stagnation zone; 2, oscillating high void fraction mixture in stagnation zone; 3, flow path; 4, rigid tubes)

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Figure 14

Coherences between the local vold fraction fluctuation and the dynamic lift and drag forces for 80% void fraction; [(a) and (b)] void fraction fluctuation at L60deg-C and drag force; [(c) and (d)] void fraction fluctuation at U90deg-L and lift force, at 5m∕s and 10m∕s pitch flow velocities, respectively

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Figure 4

Typical dynamic force spectra for 80% void fraction at 5m∕s pitch flow velocity; (a) lift force spectra; (b) drag force spectra

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Figure 5

Typical dynamic force spectra for 80% void fraction at 10m∕s pitch flow velocity; (a) lift force spectra; (b) drag force spectra

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Figure 6

Power spectra of the local void fraction fluctuation at four different positions on the right side of the main flow path for 80% void fraction at 5m∕s pitch flow velocity; (a) L60deg position, (b) L90deg position, (c) U60deg position, and (d) U90deg position

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Figure 9

Power spectra of the local void fraction fluctuation at four different positions on the left side of the main flow path for 80% void fraction at 10m∕s pitch flow velocity; (a) L60deg position, (b) L90deg position, (c) U60deg position, and (d) U90deg position

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Figure 10

Power spectra of the local void fraction fluctuation at four different positions along the centerline of the main flow path for 80% void fraction at 5m∕s pitch flow velocity; (a) L60deg position, (b) L90deg position, (c) U60deg position, and (d) U90deg position

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Figure 11

Power spectra of the local void fraction fluctuation at four different positions along the centerline of the main flow path for 80% void fraction at 10m∕s pitch flow velocity; (a) L60deg position, (b) L90deg position, (c) U60deg position, and (d) U90deg position

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Figure 12

Power spectra of the local void fraction fluctuation at points L0 and L1 of U90deg positions; [(a) and (b)] 80% void fraction at 5m∕s pitch flow velocity; [(c) and (d)] for 80% void fraction at 10m∕s pitch flow velocity, respectively

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