Towards a Validation Database for Simulation of Fluidelastic Instability in Normal Triangular Heat Exchanger Tube Arrays

2008 ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Surface Pressure ◽  
Cross Flow ◽  
Initial Step ◽  
Pressure Measurements ◽  
Dynamic Head ◽  
Flow Surface ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Large Asymmetry ◽  
Pitch Ratio

Models for fluidelastic instability are usually validated by comparing critical velocity predictions with experimental data. However, the scatter in this data make detailed validation problematic. As an initial step towards providing a validation database for fluidelastic instability, surface pressure measurements are presented for a cylinder in the third row of three normal triangular tube arrays (P/d = 1.32; 1.58; 1.97) with air cross flow. Surface pressure measurements were also made when the cylinder was statically displaced. Forces were calculated from the pressure measurements enabling an understanding of the force generation mechanism. The results show that the fluid force coefficients do not scale with the dynamic head but exhibit a dependency on Reynolds number and pitch ratio. However, no simple parametrisation was found for the lift force. Jet switching was found in P/d = 1.58 even when the tube was displaced. This phenomenon resulted in the large asymmetry observed in the pressure distribution around a static cylinder.

Spanwise Correlation of Surface Pressure Fluctuations in Heat Exchanger Tube Arrays

2010 ◽  
Author(s):  
John Mahon ◽  
Paul Cheeran ◽  
Craig Meskell
Keyword(s):  
Heat Exchanger ◽  
Surface Pressure ◽  
Pressure Fluctuations ◽  
Cross Flow ◽  
Fretting Wear ◽  
Heat Exchanger Tube ◽  
Tube Arrays ◽  
Pitch Ratio ◽  
Excitation Mechanisms ◽  
Exchanger Tube

An experimental study of the surface spanwise pressure on a cylinder in the third row of two normal triangular tube arrays (P/d = 1.32 and 1.58) with air cross flow has been conducted. A range of flow velocities were examined. The correlation of surface pressure fluctuations due to various vibration excitation mechanisms along the span of heat exchanger tubes has been assessed. The turbulent buffeting is found to be uncorrelated along the span which is consistent with generally accepted assumptions in previous studies. Vortex shedding and acoustic resonances were well correlated along the span of the cylinder, with correlations lengths approaching the entire length of the cylinder. Jet switching was observed in the pitch ratio of 1.58 and was found to be correlated along the cylinder, although the spatial behaviour is complex. This result suggests that the excitation force used in fretting wear models may need to be updated to include jet switching in the calculation.

Estimation of the Time Delay Associated With Damping Controlled Fluidelastic Instability in a Normal Triangular Tube Array

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
John Mahon ◽  
Craig Meskell
Keyword(s):  
Time Delay ◽  
Cross Flow ◽  
Fluid Forces ◽  
Fluidelastic Instability ◽  
Order Of Magnitude ◽  
Sample Frequency ◽  
Pitch Ratio ◽  
Parameterized Model ◽  
Semi Empirical ◽  
Insight Into

Fluidelastic instability (FEI) produces large amplitude self-excited vibrations close to the natural frequency of the structure. For fluidelastic instability caused by the damping controlled mechanism, there is a time delay between tube motion and the resulting fluid forces but magnitude and physical cause of this is unclear. This study measures the time delay between tube motion and the resulting fluid forces in a normal triangular tube array with a pitch ratio of 1.32 subject to air cross-flow. The instrumented cylinder was forced to oscillate in the lift direction at three excitation frequencies for a range of flow velocities. Unsteady surface pressures were monitored with a sample frequency of 2 kHz at the mid plane of the instrumented cylinder. The instantaneous fluid forces were obtained by integrating the surface pressure data. A time delay between the tube motion and resulting fluid forces was obtained. The nondimensionalized time delay was of the same order of magnitude assumed in the semi-empirical quasi-steady model (i.e., τ2 = 0.29 d/U). Although, further work is required to provide a parameterized model of the time delay which can be embedded in a model of damping controlled fluidelastic forces, the data already provides some insight into the physical mechanism responsible.

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

2015 ◽  
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.

Two-Phase Flow-Induced Vibration of Parallel Triangular Tube Arrays With Asymmetric Support Stiffness

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
Paul Feenstra ◽  
David S. Weaver ◽  
Tomomichi Nakamura
Keyword(s):  
Two Phase Flow ◽  
Cross Flow ◽  
Phase Flow ◽  
Heat Exchanger Tube ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Tube Arrays ◽  
Tube Bundles ◽  
Pitch Ratio ◽  
Exchanger Tube

Laboratory experiments were conducted to determine the flow-induced vibration response and fluidelastic instability threshold of model heat exchanger tube bundles subjected to a cross-flow of refrigerant 11. Tube bundles were specially built with tubes cantilever-mounted on rectangular brass support bars so that the stiffness in the streamwise direction was about double that in the transverse direction. This was designed to simulate the tube dynamics in the U-bend region of a recirculating-type nuclear steam generator. Three model tube bundles were studied, one with a pitch ratio of 1.49 and two with a smaller pitch ratio of 1.33. The primary intent of the research was to improve our understanding of the flow-induced vibrations of heat exchanger tube arrays subjected to two-phase cross-flow. Of particular concern was to compare the effect of the asymmetric stiffness on the fluidelastic stability threshold with that of axisymmetric stiffness arrays tested most prominently in literature. The experimental results are analyzed and compared with existing data from literature using various definitions of two-phase fluid parameters. The fluidelastic stability thresholds of the present study agree well with results from previous studies for single-phase flow. In two-phase flow, the comparison of the stability data depends on the definition of two-phase flow velocity.

A Study on Stream-Wise Oscillation of Cylinder Arrays: Effect of Pitch Ratio

2009 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Takafumi Yoshikawa ◽  
Taku Yoshimura ◽  
Hironobu Kondo
Keyword(s):  
High Speed ◽  
Flow Direction ◽  
Cross Flow ◽  
Video Camera ◽  
Strain Gages ◽  
Flow Oscillation ◽  
Digital Video Camera ◽  
Cylinder Arrays ◽  
Tube Arrays ◽  
Pitch Ratio

The importance of the in-flow oscillation of a single cylinder in cross-flow has been spotlighted since an accident in a FBR-type reactor. However, the in-flow oscillation can be observed in tube arrays of heat exchangers. Previous reports show some interesting phenomena on the oscillation of cylinder arrays, which have a same pitch between cylinders. This paper shows the effect of the pitch ratio of a cylinder array on the characteristics of those phenomena, especially in in-flow direction, where every cylinder can move only in this direction. The motion of cylinders is measured by attached strain gages and by a high-speed digital video camera.

Streamwise Fluidelastic Instability of Tube Arrays in Two-Phase Cross Flow

2014 ◽  
Author(s):  
Stephen Olala ◽  
Njuki W. Mureithi
Keyword(s):  
Nuclear Power ◽  
Single Phase ◽  
Cross Flow ◽  
Force Measurements ◽  
Two Phase Flows ◽  
Two Phase ◽  
Fluid Force ◽  
Void Fractions ◽  
Tube Arrays ◽  
Fluidelastic Instability

In-plane instability of tube arrays has not been a major concern to steam generator designers until recently following observations of streamwise tube failure in a nuclear power plant in U.S.A. However, modeling of fluidelastic instability in two-phase flows still remains a challenge. In the present work, detailed steady fluid force measurements for a kernel of an array of tubes in a rotated triangular tube array of P/D=1.5 subjected to air-water two-phase flows for a series of void fractions and a Reynolds number (based on the pitch velocity), Re = 7.2 × 104 has been conducted. The measured steady fluid force coefficients and their derivatives, with respect to streamwise static displacements of the central tube, are employed in the quasi-steady model [1, 2], originally developed for single phase flows, to analyze in-plane fluidelastic instability of multiple flexible arrays in two-phase flows. The results are consistent with dynamic stability tests [3].

The Cross-Flow Response of a Tube Array in Water—A Comparison With the Same Array in Air

1982 ◽  
Vol 104 (3) ◽  
pp. 139-146 ◽  
Author(s):  
D. S. Weaver ◽  
D. Koroyannakis
Keyword(s):  
Cross Flow ◽  
Added Mass ◽  
Response Curves ◽  
Flow Response ◽  
Tube Arrays ◽  
Mass Coefficient ◽  
Pitch Ratio ◽  
Added Mass Coefficient ◽  
The Stability ◽  
Wind Tunnel Study

A water tunnel study was conducted on a parallel triangular array of tubes with a pitch ratio of 1.375. The array was geometrically identical to that used previously in a wind tunnel study so that the tube response to cross flow could be compared. It was seen that the response curves for tube arrays in water are much less regular than those in air, creating ambiguity in defining the stability threshold. The irregularities are seen to be associated with shifts in relative tube mode and frequency. Arrays in water apparently first become unstable in one of the lowest frequencies of the band of frequencies associated with a given structural mode. The added mass coefficient computed from the observed frequency at instability is a little larger than the largest added mass coefficient obtained from existing theory for tube arrays in quiescent fluid.

Numerical Simulation of Cross-Flow-Induced Fluidelastic Vibration of Tube Arrays and Comparison With Experimental Results

1995 ◽  
Vol 117 (1) ◽  
pp. 31-39 ◽  
Author(s):  
F. L. Eisinger ◽  
M. S. M. Rao ◽  
D. A. Steininger ◽  
K. H. Haslinger
Keyword(s):  
Tube Bundle ◽  
Experimental Testing ◽  
Nonlinear Modeling ◽  
Cross Flow ◽  
Published Data ◽  
Nonlinear Structure ◽  
Numerical Studies ◽  
Tube Arrays ◽  
Fluidelastic Instability ◽  
Good Agreement

Tube arrays exposed to air, gas or liquid cross-flow can vibrate due to vortex-shedding, turbulence, or fluidelastic instability. The major emphasis of this paper is on the phenomenon of fluidelastic instability (or fluidelastic vibration). A numerical model is applied to the simulation of fluidelastic vibration of representative tubes in a tube bundle, based on S. S. Chen’s unsteady flow theory. The results are validated against published data based on linear cases. The model is then applied to a nonlinear structure of a U-bend tube bundle with clearances at supports, and the computed results compared to those obtained by experimental testing. The numerical studies were performed using the ABAQUS-EPGEN finite element code using a special subroutine incorporating fluidelastic forces. It is shown that the results of both the linear and nonlinear modeling are in good agreement with experimental data.

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