Theoretical investigation of fluidelastic instability of a rotated triangular tube array in two-phase flow

The time delay is a key parameter for modeling fluidelastic instability, especially the damping controlled mechanism. It can be determined experimentally by measuring directly the time lag between the tube motion and the induced fluid forces. The fluid forces may be obtained by integrating the pressure field around the moving tube. However, this method faces certain difficulties in two-phase flow since the high turbulence and the non-uniformity of the flow may increase the randomness of the measured force. To overcome this difficulty, an innovative method for extracting the time delay inherent to the quasi-steady model for fluidelastic instability is proposed in this study. Firstly, experimental measurements of unsteady and quasi-static fluid forces (in the lift direction) acting on a tube subject to two-phase flow were conducted. The unsteady fluid forces were measured by exciting the tube using a linear motor. These forces were measured for a wide range of void fraction, flow velocities and excitation frequencies. The experimental results showed that the unsteady fluid forces could be represented as single valued function of the reduced velocity (flow velocity reduced by the excitation frequency and the tube diameter). The time delay was determined by equating the unsteady fluid forces with the quasi-static forces. The results given by this innovative method of measuring the time delay in two-phase flow were consistent with theoretical expectations. The time delay could be expressed as a linear function of the convection time and the time delay parameter was determined for void fractions ranging from 60% to 90%. Fluidelastic instability calculations were also performed using the quasi-steady model with the newly measured time delay parameter. Previously conducted stability tests provided the experimental data necessary to validate the theoretical results of the quasi-steady model. The validity of the quasi-steady model for two-phase flow was confirmed by the good agreement between its results and the experimental data. The newly measured time delay parameter has improved significantly the theoretical results, especially for high void fractions (90%). However, the model could not be verified for void fractions lower or equal to 50% due to the limitation of the current experimental setup. Further studies are consequently required to clarify this point. Nevertheless, this model can be used to simulate the flow induced vibrations in steam generators’ tube bundles as their most critical parts operate at high void fractions (≥ 60%).

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Vibration of a Tube Bundle in Two-Phase Freon Cross-Flow

Journal of Pressure Vessel Technology ◽

10.1115/1.2842130 ◽

1995 ◽

Vol 117 (4) ◽

pp. 321-329 ◽

Cited By ~ 36

Author(s):

M. J. Pettigrew ◽

C. E. Taylor ◽

J. H. Jong ◽

I. G. Currie

Keyword(s):

Two Phase Flow ◽

Tube Bundle ◽

Density Ratio ◽

Cross Flow ◽

Flow Regimes ◽

Phase Flow ◽

Two Phase ◽

Void Fractions ◽

Fluidelastic Instability ◽

First Results

Two-phase cross-flow exists in many shell-and-tube heat exchangers. The U-bend region of nuclear steam generators is a prime example. Testing in two-phase flow simulated by air-water provides useful results inexpensively. However, two-phase flow parameters, in particular surface tension and density ratio, are considerably different in air-water than in steam-water. A reasonable compromise is testing in liquid-vapor Freon, which is much closer to steam-water while much simpler experimentally. This paper presents the first results of a series of tests on the vibration behavior of tube bundles subjected to two-phase Freon cross-flow. A rotated triangular tube bundle of tube-to-diameter ratio of 1.5 was tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, and damping were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability. Generally, random turbulence excitation forces are much lower in Freon than in air-water. Damping is very dependent on void fraction, as expected.

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Experimental and theoretical investigation on two-phase flow characteristics and pressure drop during flow condensation in heat transport pipeline

Applied Thermal Engineering ◽

10.1016/j.applthermaleng.2014.02.028 ◽

2014 ◽

Vol 66 (1-2) ◽

pp. 365-374 ◽

Cited By ~ 9

Author(s):

Cong Guo ◽

Tao Wang ◽

Xuegong Hu ◽

Dawei Tang

Keyword(s):

Pressure Drop ◽

Heat Transport ◽

Theoretical Investigation ◽

Two Phase Flow ◽

Flow Characteristics ◽

Phase Flow ◽

Two Phase ◽

Flow Condensation

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Two-Phase Flow-Induced Vibration: An Overview (Survey Paper)

Journal of Pressure Vessel Technology ◽

10.1115/1.2929583 ◽

1994 ◽

Vol 116 (3) ◽

pp. 233-253 ◽

Cited By ~ 86

Author(s):

M. J. Pettigrew ◽

C. E. Taylor

Keyword(s):

Two Phase Flow ◽

Cross Flow ◽

Axial Flow ◽

Random Excitation ◽

Phase Flow ◽

Flow Induced Vibration ◽

Two Phase ◽

Vibration Excitation ◽

Fluidelastic Instability ◽

Excitation Mechanisms

Two-phase flow exists in many industrial components. To avoid costly vibration problems, sound technology in the area of two-phase flow-induced vibration is required. This paper is an overview of the principal mechanisms governing vibration in two-phase flow. Dynamic parameters such as hydrodynamic mass and damping are discussed. Vibration excitation mechanisms in axial flow are outlined. These include fluidelastic instability, phase-change noise, and random excitation. Vibration excitation mechanisms in cross-flow, such as fluidelastic instability, periodic wake shedding, and random excitation, are reviewed.

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Fluidelastic Instability of U-bend Tube Array Based on Correlated Unsteady Fluid Force in Two-Phase Flow

The proceedings of the JSME annual meeting ◽

10.1299/jsmemecjo.2003.7.0_285 ◽

2003 ◽

Vol 2003.7 (0) ◽

pp. 285-286

Author(s):

Tomomichi NAKAMURA ◽

Kengo SHIMAMURA ◽

Toshihiko IWASE ◽

Seishi NISHIDA

Keyword(s):

Two Phase Flow ◽

Phase Flow ◽

Two Phase ◽

Fluid Force ◽

Fluidelastic Instability ◽

Unsteady Fluid

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Vibration Behavior of Rotated Triangular Tube Bundles in Two-Phase Cross Flows

Journal of Pressure Vessel Technology ◽

10.1115/1.1462045 ◽

2002 ◽

Vol 124 (2) ◽

pp. 144-153 ◽

Cited By ~ 32

Author(s):

M. J. Pettigrew ◽

C. E. Taylor ◽

V. P. Janzen ◽

T. Whan

Keyword(s):

Void Fraction ◽

Two Phase Flow ◽

Flow Regimes ◽

Intermittent Flow ◽

Phase Flow ◽

Two Phase ◽

Vibration Behavior ◽

Void Fractions ◽

Tube Bundles ◽

Fluidelastic Instability

The results of a series of tests describing the vibration behavior of several rotated triangular tube bundles subjected to two-phase cross flows are presented. Tube bundles with a pitch-to-diameter ratio of approximately 1.5 were tested over a broad range of void fractions and mass fluxes. Fluidelastic instability, random turbulence excitation, hydrodynamic mass, two-phase damping and local void-fraction were investigated. Well-defined fluidelastic instabilities were observed in continuous two-phase flow regimes. However, intermittent two-phase flow regimes had a dramatic effect on fluidelastic instability leading to lower than expected threshold flow velocities for instability. This effect was more pronounced in Freon two-phase flow than in air-water, and appeared well correlated to the transition between continuous and intermittent flow regimes. Generally, random turbulence excitation forces were much lower in Freon than in air-water. Although very dependent on void fraction, as expected, damping was quite similar in air-water and Freon.

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