An Improved Scaling Model of Buffeting Lift Forces in Air-Water Flows

2011 ◽  
Vol 133 (2) ◽  
Author(s):  
Sylviane Pascal-Ribot ◽  
Yves Blanchet
Keyword(s):  
Cross Flow ◽  
Tube Diameter ◽  
Two Phase Flows ◽  
Two Phase ◽  
Scaling Model ◽  
Void Fractions ◽  
Precise Knowledge ◽  
Series Of Experiments ◽  
Lift Forces ◽  
Different Diameters

This paper presents the results of a series of experiments to study the influence of diameter on the loading of a single rigid cylinder subjected to air-water cross-flow. Five rigid cylinders of same length and different diameters (12.15×10−3 m to 31.9×10−3 m) were tested over void fractions ranging from 10% to 80%. The fluctuating lift forces on the cylinder are measured and represented in the form of power spectral density. A scaling model of these forces previously developed from one series of experiments with one tube diameter (12.15×10−3 m) is tested on these new results by investigating the effect of tube diameter D. Unlike single phase results where the force spectra vary as D3, it is shown that for two-phase flows, the force spectra vary as D2. The experimental data collapse remarkably well. Both local void fraction and flow regime appear to be sensitive parameters. It confirms the importance of a precise knowledge of the local characteristics of two-phase flows in the study of buffeting forces mechanisms.

An Improved Scaling Model of Buffeting Lift Forces in Air-Water Flows

2007 ◽  
Author(s):  
Sylviane Pascal-Ribot ◽  
Yves Blanchet
Keyword(s):  
Cross Flow ◽  
Tube Diameter ◽  
Two Phase Flows ◽  
Two Phase ◽  
Scaling Model ◽  
Void Fractions ◽  
Precise Knowledge ◽  
Series Of Experiments ◽  
Lift Forces ◽  
Different Diameters

This paper presents the results of a series of experiments to study the loading of a single rigid cylinder subjected to air-water cross-flow. Five rigid cylinders of same length and different diameters (12.15×10−3 m to 31.9×10−3 m) were tested over void fractions ranging from 10% to 80%. The fluctuating lift forces on the cylinder are measured and represented in the form of power spectral density. A scaling model of these forces previously developed from one series of experiments with one tube diameter (12.15×10−3 m) is tested on these new results by investigating the effect of tube diameter D. Unlike single phase results where the force spectra vary as D3, it is shown that for two-phase flows the force spectra vary as D2. The experimental data collapse remarkably well. Both local void fraction and flow regime appear to be sensitive parameters. It confirms the importance of a precise knowledge of the local characteristics of two-phase flows in the study of buffeting forces mechanisms.

Fluidelastic Instability of Flexible Tubular Cylinders Subjected to Two-Phase Internal Flow

2003 ◽  
Author(s):  
Christine Monette ◽  
Michel J. Pettigrew
Keyword(s):  
Internal Flow ◽  
Gas Flows ◽  
Two Phase Flows ◽  
Two Phase ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
Piping Systems ◽  
Phase Liquid ◽  
Series Of Experiments ◽  
Different Diameters

The fluidelastic instability behaviour of flexible cylinders subjected to internal single-phase (liquid or gas) flows is now reasonably well understood. Although many piping systems operate in two-phase flows, so far very little work has been done to study their dynamic behaviour under such flows. This paper presents the results of a series of experiments to study the fluidelastic instability behaviour of flexible tubular cylinders subjected to two-phase internal flow. Several flexible cylinders of different diameters, lengths and flexural rigidities were tested over a broad range of flow velocities and void fractions in an air-water loop to simulate two-phase flows. Well-defined fluidelastic instabilities were observed in two-phase flows. The existing theory to formulate the fluidelastic behaviour under internal flow was developed further to take into account two-phase flow. The agreement between the experimental results and the modified theory is remarkably good. However, it depends on using an appropriate model to formulate the characteristics of the two-phase flows.

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].

New Experimental Data and Analysis for Two-Phase Flow-Induced Vibration of Tube Bundles: Preliminary Results

2003 ◽  
Author(s):  
Deepanjan Mitra ◽  
Vijay K. Dhir ◽  
Ivan Catton
Keyword(s):  
Two Phase Flow ◽  
Structural Parameters ◽  
Cross Flow ◽  
Instability Criterion ◽  
Phase Flow ◽  
Flow Induced Vibration ◽  
Two Phase ◽  
Void Fractions ◽  
Comparison Of The Results ◽  
Square Array

In the past, fluid-elastic instability in two-phase flow has been largely investigated with air-water flow. In this work, new experiments are conducted in air-water cross-flow with a fully flexible 5 × 3 normal square array having pitch-to-diameter ratio of 1.4. The tubes have a diameter of 0.016 m and a length of 0.21 m. The vibrations are measured using strain gages installed on piano wires used to suspend the tubes. Experiments are carried out for void fractions from 0%–30%. A comparison of the results of the current tests with previous experiments conducted in air-water cross-flow shows that instability occurs earlier in a fully flexible array as compared to a flexible tube surrounded by rigid tubes in an array. An attempt is made to separate out the effects of structural parameters of three different experimental datasets by replotting the instability criterion by incorporating the instability constant K, in the reduced velocity parameter.

Fluidelastic Instability and Periodic Fluid Forces in a Normal Triangular Tube Bundle Subjected to Air-Water Flow

2010 ◽  
Author(s):  
G. Ricciardi ◽  
M. J. Pettigrew ◽  
N. W. Mureithi
Keyword(s):  
Two Phase Flow ◽  
Tube Bundle ◽  
Fatigue Cracks ◽  
Cross Flow ◽  
Fretting Wear ◽  
Phase Flow ◽  
Steam Generators ◽  
Two Phase ◽  
Fluid Forces ◽  
Void Fractions

Two-phase flow in power plant steam generators can induce tube vibrations, which may cause fretting-wear and even fatigue cracks. It is therefore important to understand the relevant two-phase flow-induced vibration mechanisms. Fluidelastic instabilities in cross-flow are known to cause the most severe vibration response in the U-bend region of steam generators. This paper presents test results of the vibration of a normal triangular tube bundle subjected to air-water cross-flow. The test section presents 31 flexible tubes. The pitch-to-diameter ratio of the bundle is 1.5, and the tube diameter is 38 mm. Tubes were flexible in the lift direction. Seven tubes were instrumented with strain gauges to measure their displacements. A broad range of void fractions (from 10% to 90%) and fluid velocities (up to 13 m/s) were tested. Fluidelastic instabilities were observed for void fractions between 10% and 60%. Periodic fluid forces were also observed. The results are compared with those obtained with the rotated triangular tube bundle, showing that the normal triangular configuration is more stable than the rotated triangular configuration.

Further Study of Quasiperiodic Vibration Excitation Forces in Rotated Triangular Tube Bundles Subjected to Two-Phase Cross Flow

2009 ◽  
Vol 131 (3) ◽  
Author(s):  
C. Zhang ◽  
M. J. Pettigrew ◽  
N. W. Mureithi
Keyword(s):  
Flow Velocity ◽  
Cross Flow ◽  
Fretting Wear ◽  
Force Frequency ◽  
Two Phase ◽  
Vibration Excitation ◽  
Tube Bundles ◽  
Excitation Force ◽  
Lift Forces ◽  
Drag And Lift

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 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. Somewhat unexpected but significant quasiperiodic forces in both the drag and lift directions were measured. These forces are generally larger in the drag direction. However, the excitation force frequency is relatively low (i.e., 3–6 Hz) and not directly dependent on flow velocity in the drag direction. On the other hand, much higher frequencies (up to 16 Hz) were observed in the lift direction at the higher flow velocities. The frequency appears directly related to flow velocity in the lift direction. The present work aims at (1) providing further evidence of the quasiperiodic lift force mechanism, (2) determining the effect of cylinder position on such quasiperiodic drag and lift forces, and (3) verifying the existence of quasiperiodic drag and lift forces in a more realistic larger tube array. The program was carried out with two rotated triangular tube arrays of different width subjected to air/water flow to simulate two-phase mixtures from liquid to 95% void fraction. Both the dynamic lift and drag forces were measured with strain gauge instrumented cylinders.

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

1995 ◽  
Vol 117 (4) ◽  
pp. 321-329 ◽  
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.

scholarly journals 3D gas-liquid interfaces and flow characteristics of two-phase flows in horizontal tubes

2021 ◽  
Vol 2116 (1) ◽  
pp. 012072
Author(s):  
Jingzhi Zhang ◽  
Bengt Sunden ◽  
Vishwas Wadekar ◽  
Zan Wu
Keyword(s):  
Flow Pattern ◽  
Void Fraction ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Patterns ◽  
Industrial Applications ◽  
Liquid Interfaces ◽  
Two Phase Flows ◽  
Two Phase ◽  
Void Fractions

Abstract In order to investigate the characteristics of gas-liquid two-phase flows in horizontal mini circular tubes with inner diameters of 3.14 and 6.68 mm, a prism is adopted to improve the light path in the visualization experimental setup. The front and top views of air-water two-phase flow patterns in two tubes are captured synchronously based on the improved method. Three-dimensional gas-liquid interfaces, flow pattern maps, and void fraction are obtained. The experimental results show that tube diameters have significant effects on flow patterns transition lines in the flow pattern maps, but the void fractions are independent on channel sizes. The effect of gravity gradually decreases with decreasing tube diameter, while that of surface tension is enhanced. As a consequence, the proportion of annular flow in flow pattern map increases in mini tubes, while the reverse is true for the stratified flow whose proportion decreases dramatically in mini channels. The void fraction increases with increasing gas quality. Experimental void fractions obtained using the three-dimensional gas-liquid interfaces fit well with correlations in the open literature. The shape of PDF distributions varies with flow patterns, which could be used to identify flow patterns in industrial applications.

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