Fluctuating Forces in U-Tubes Subjected to Internal Two-Phase Flow

2005 ◽  
Author(s):  
Jean-Luc Riverin ◽  
Michel J. Pettigrew
Keyword(s):  
Two Phase Flow ◽  
Periodic Structures ◽  
Internal Flow ◽  
Resonance Phenomenon ◽  
Dimensionless Frequency ◽  
Phase Flow ◽  
Two Phase ◽  
Power Spectral ◽  
Wide Range ◽  
Periodic Components

Severe in-plane vibrations were observed in a series of 20-mm dia. PVC vertical U-tubes of different elbow geometries subjected to air-water internal flow. An experimental study was undertaken to investigate the excitation mechanism. Vibration response, excitation forces and fluctuating properties of two-phase flow were measured over a wide range of flow conditions. The experimental results show that the observed vibrations are due to a resonance phenomenon between periodic momentum flux fluctuations of two-phase flow and the first modes of U-tubes. The excitation forces consist of a combination of narrow-band and periodic components, with a predominant frequency that increases proportionally to flow velocity. For a given void fraction, the force spectra for various flow velocities and elbow geometries coincide generally well on a plot of the normalized power spectral density as a function of a dimensionless frequency. The predominant frequencies of excitation agree with recent results on the characteristics of periodic structures in two-phase flow.

Vibration Excitation Forces Due to Two-Phase Flow in Piping Elements

2006 ◽  
Vol 129 (1) ◽  
pp. 7-13 ◽  
Author(s):  
J.-L. Riverin ◽  
M. J. Pettigrew
Keyword(s):  
Two Phase Flow ◽  
Periodic Structures ◽  
Resonance Phenomenon ◽  
Piping System ◽  
Dimensionless Frequency ◽  
Phase Flow ◽  
Two Phase ◽  
Vibration Excitation ◽  
Wide Range ◽  
Periodic Components

Severe vibrations were observed in a small piping system comprising two elbows and straight sections configured in the form of a U and subjected to air-water internal two-phase flow. An experimental study was undertaken to investigate the governing vibration excitation mechanism. Vibration response, excitation forces, and fluctuating properties of two-phase flow were measured over a wide range of flow conditions. The results show that the observed vibrations are due to a resonance phenomenon between periodic momentum flux fluctuations of two-phase flow and the first modes of the piping system. The excitation forces consist of a combination of narrow-band and periodic components, with a predominant frequency that increases proportionally to flow velocity. For a given void fraction, the force spectra for various flow velocities and elbow geometries show little scatter on a plot of a normalized power spectral density as a function of a dimensionless frequency. The predominant frequencies of excitation agree with recent results on the characteristics of periodic structures in two-phase flow.

Time Domain Simulation of the Vibration of a Steam Generator Tube Subjected to Fluidelastic Forces Induced by Two-Phase Cross-Flow

2013 ◽  
Vol 135 (3) ◽  
Author(s):  
Téguewindé Sawadogo ◽  
Njuki Mureithi
Keyword(s):  
Steam Generator ◽  
Two Phase Flow ◽  
Work Rate ◽  
Fretting Wear ◽  
Phase Flow ◽  
Reference Case ◽  
Two Phase ◽  
Steam Generator Tube ◽  
Wide Range ◽  
Instability Regime

Having previously verified the quasi-steady model under two-phase flow laboratory conditions, the present work investigates the feasibility of practical application of the model to a prototypical steam generator (SG) tube subjected to a nonuniform two-phase flow. The SG tube vibration response and normal work-rate induced by tube-support interaction are computed for a range of flow conditions. Similar computations are performed using the Connors model as a reference case. In the quasi-steady model, the fluid forces are expressed in terms of the quasi-static drag and lift force coefficients and their derivatives. These forces have been measured in two-phase flow over a wide range of void fractions making it possible to model the effect of void fraction variation along the tube span. A full steam generator tube subjected to a nonuniform two-phase flow was considered in the simulations. The nonuniform flow distribution corresponds to that along a prototypical steam-generator tube based on thermal-hydraulic computations. Computation results show significant and important differences between the Connors model and the two-phase flow based quasi-steady model. While both models predict the occurrence of fluidelastic instability, the predicted pre-instability and post instability behavior is very different in the two models. The Connors model underestimates the flow-induced negative damping in the pre-instability regime and vastly overestimates it in the post instability velocity range. As a result the Connors model is found to underestimate the work-rate used in the fretting wear assessment at normal operating velocities, rendering the model potentially nonconservative under these practically important conditions. Above the critical velocity, this model largely overestimates the work-rate. The quasi-steady model on the other hand predicts a more moderately increasing work-rate with the flow velocity. The work-rates predicted by the model are found to be within the range of experimental results, giving further confidence to the predictive ability of the model. Finally, the two-phase flow based quasi-steady model shows that fluidelastic forces may reduce the effective tube damping in the pre-instability regime, leading to higher than expected work-rates at prototypical operating velocities.

Void Fractions in Two-Phase Flow: A Correlation Based upon an Equal Velocity Head Model

1969 ◽  
Vol 184 (1) ◽  
pp. 647-664 ◽  
Author(s):  
S. L. Smith
Keyword(s):  
Two Phase Flow ◽  
Head Model ◽  
Phase Flow ◽  
Excellent Correlation ◽  
Two Phase ◽  
Void Fractions ◽  
Dynamic Head ◽  
Wide Range ◽  
Mixture Phase ◽  
Simple Physical Model

An expression is obtained for void fraction in two-phase flow based upon a simple physical model. The model assumes an annular flow regime with a liquid phase and a homogeneous mixture phase flowing with equal dynamic head. Excellent correlation is obtained with a wide range of experimental data, indicating a significant improvement over current methods.

Application of Fast Synchrotron X-ray Imaging in Velocimetry of Cavitating Flows

2021 ◽  
Author(s):  
Mingming Ge ◽  
Guangjian Zhang ◽  
Navid Nematikourabbasloo ◽  
Kamel Fezzaa ◽  
Olivier Coutier-Delgosha
Keyword(s):  
Phase Contrast ◽  
Two Phase Flow ◽  
Motion Blur ◽  
Hydrodynamic Cavitation ◽  
Phase Flow ◽  
Two Phase ◽  
X Ray ◽  
Sheet Cavitation ◽  
Contraction Ratio ◽  
Wide Range

Hydrodynamic cavitation is a complex two-phase flow phenomenon involving mass and heat transfer between liquid and vapor. It occurs in many widely-used hydraulic machines, such as pumps and marine propellers, and often leads to undesired effects like material erosion, noise, and vibration. To control these detrimental effects, the visualization of two-phase flow morphology inside the opaque cavity is a crucial point to improve the physical and numerical models of cavitation. The major challenge in experimental measurements of cavitating flow fields is the fact that multiple scattering and a direct reflection of visible light from phase boundaries make the flow optically opaque. In recent years, unlike traditional local measurements using various probes, the development of the third-generation synchrotron radiation sources promotes the application of Xray phase-contrast imaging, which enables clear visualization of boundaries between phases with different refractive indices. In this study, the partial cavity is formed in a convergent-divergent (Venturi) channel with a small contraction ratio where the relatively stable cavitation regime can be sustained in a wide range of cavitation numbers. The experiment performed at Advanced Photon Source (APS) of Argonne uses the short high-flux X-ray pulses emitted from synchrotron sources to capture fast dynamic events and minimize motion blur. The internal two-phase structures and bubble development dynamics inside the quasi-stable sheet cavitation can be identified. Aside from the detailed illustration of two-phase morphology, X-ray phase-contrast images were also used to perform velocimetry by tracking either seeded particles or phase interfaces inside the opaque regions. Through appropriate postprocessing to the recorded X-ray images of cavitation, the time resolved velocity and void fraction fields are obtained simultaneously. These unprecedented experimental data will be further explored in understanding fluid mechanics underneath the cavity, estimating slip velocity between fluid-vapor interactions, and reconstructing pressure fields for compressible flows.

CFD Prediction of Safety Valve Disc Forces Under Two Phase Flow Conditions

2018 ◽  
Author(s):  
William Dempster ◽  
Moftah Alshaikh
Keyword(s):  
Two Phase Flow ◽  
Safety Valve ◽  
Phase Flow ◽  
Complex Flow ◽  
Two Phase ◽  
Wide Range ◽  
Valve Disc ◽  
Valve Dynamics ◽  
Inlet Conditions ◽  
Industrial Refrigeration

At present there are very few published works on prediction based methods to establish the forces that act on safety valves during two-phase operation. This means that the valve dynamics and resulting opening and closure are uncertain for a wide range of complex flow applications. This paper describes a study whereby a safety valve, primarily developed for the industrial refrigeration sector is investigated for a range of steady state high gas mass fraction inlet conditions, (gas mass quality 1-0.2) and the disc force characteristics measured for valve choked conditions. The highly compressible two phase flow processes are modelled using an Euler–Euler two fluid CFD approach and the results compared with the experiments. Results indicate that CFD approaches can reasonably capture the key processes but deficiencies exist due to the prediction of two phase built up backpressure in the valve. The methods and data trends are discussed to show the effectiveness of current modelling approaches.

Research Analysis and Experiment Study on Flow Field of Hydrodynamic Coupling

2011 ◽  
Vol 418-420 ◽  
pp. 2006-2011
Author(s):  
Rui Zhang ◽  
Cheng Jian Sun ◽  
Yue Wang
Keyword(s):  
Flow Field ◽  
Cfd Simulation ◽  
Two Phase Flow ◽  
Three Dimensional ◽  
Internal Flow ◽  
Phase Flow ◽  
Complex Flow ◽  
Two Phase ◽  
Operation Conditions ◽  
Hydrodynamic Coupling

CFD simulation and PIV test technology provide effective solution for revealing the complex flow of hydrodynamic coupling’s internal flow field. Some articles reported that the combination of CFD simulation and PIV test can be used for analyzing the internal flow field of coupling, and such analysis focuses on one-phase flow. However, most internal flow field of coupling are gas-fluid two-phase flow under the real operation conditions. In order to reflect the gas-fluid two-phase flow of coupling objectively, CFD three-dimensional numerical simulation is conducted under two typical operation conditions. In addition, modern two-dimensional PIV technology is used to test the two-phase flow. This method of combining experiments and simulation presents the characteristics of the flow field when charging ratios are different.

Transition of Bubbly to Slug Flow in a Short Vertical Channel of Gas-Liquid Two-Phase Flow

2014 ◽  
Vol 881-883 ◽  
pp. 721-725
Author(s):  
Mohd Zamri Zainon ◽  
Mohd Ardan Zubir ◽  
Rahizar Ramli
Keyword(s):  
Slug Flow ◽  
Two Phase Flow ◽  
Vertical Channel ◽  
Superficial Velocity ◽  
Phase Flow ◽  
Flow Loop ◽  
Two Phase ◽  
Slip Ratio ◽  
Wide Range ◽  
Simple Flow

Transitions of bubbly to slug flow have been investigated for wide range of flow conditions via visualization technique. The effects of velocities of both phases were examined with variety of combinations and the experimentations were focused on the air-water flow with an industrial scale two-phase flow loop. The results show that the formations of slugs were easy with the increasing gas superficial velocity during a fixed liquid superficial velocity and were difficult when velocity of the liquid phase increases. These transitions were then evaluated using the ratio of velocities of both phases or called the slip ratio and from there a simple flow pattern map was constructed.

Use of a Bubble Tracking Method for Prediction of Downhole Natural Separation Efficiency

2005 ◽  
Vol 127 (4) ◽  
pp. 479-486
Author(s):  
Bin Liu ◽  
Mauricio Prado
Keyword(s):  
Experimental Data ◽  
Flow Field ◽  
Single Phase ◽  
Two Phase Flow ◽  
Separation Efficiency ◽  
Phase Flow ◽  
Two Phase ◽  
Tracking Method ◽  
Wide Range ◽  
Natural Separation

For any pumping artificial lift system in the petroleum industry, the free gas significantly affects the performance of the pump and the system above the pump. A model, though not a complete two-phase flow model, has been developed for the effective prediction of separation efficiency across a wide range of production conditions. The model presented is divided into two main parts, the single-phase flow-field solution and the bubble-tracking method. The first part of the model solves the single-phase liquid flow field using the computational fluid dynamics approach. Then, a simple bubble-tracking method was applied to estimate the down-hole natural separation efficiency for two-phase flow. A comparison between the results of the model and the experimental data was conducted. It shows a very good agreement with the experimental data for lower gas void fractions (bubble flow regime).

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