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

2003 ◽  
Author(s):  
Tomomichi Nakamura ◽  
Kengo Shimamura ◽  
Toshihiko Iwase ◽  
Seishi Nishida
Keyword(s):  
Two Phase Flow ◽  
Phase Flow ◽  
Tube Axis ◽  
Flow Conditions ◽  
Average Correlation ◽  
Two Phase ◽  
Fluid Force ◽  
Fluidelastic Instability ◽  
Short Span ◽  
Unsteady Fluid

The fluidelastic instability threshold of tube arrays can be estimated using measured unsteady fluid force. It is usually assumed that the fluid force is completely correlated along the tube axis; this may be true in single phase flow. However, the flow in the two-phase flow is no longer steady, in space or in time. Thus, the correlation of the fluid force acting along the tube axis should be introduced. There are very few measured data for the correlation of the fluid force in two-phase flow, and it is difficult to deduce from measured time-history fluid data, such as the void fraction or the flow velocity. In this report, the average correlation length is derived from critical flow velocities of U-bend tubes in several two-phase flow conditions, based on an approximate theory for the two-phase flow condition when the unsteady fluid force for a short span model has been measured. As a result, the average correlation length gives the critical flow velocities of each U-bend tube. The result gives a good explanation why the critical factor in the U-bend tube is larger than that in short span models. This method can be a new estimation of the fluidelastic instability of U-bend tubes in two-phase flow conditions.

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

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

A Method for Extracting the Time Delay From the Unsteady and Quasi-Steady Fluidelastic Forces in Two-Phase Flow

2013 ◽  
Author(s):  
Teguewinde Sawadogo ◽  
Njuki Mureithi
Keyword(s):  
Time Delay ◽  
Two Phase Flow ◽  
Phase Flow ◽  
Two Phase ◽  
Fluid Forces ◽  
Void Fractions ◽  
Fluidelastic Instability ◽  
Measured Time ◽  
Unsteady Fluid ◽  
Theoretical Results

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%).

Quasi-Static Forces and Stability Analysis in a Triangular Tube Bundle Subjected to Two-Phase Cross-Flow

2007 ◽  
Author(s):  
Soroush Shahriary ◽  
Njuki W. Mureithi ◽  
Michel J. Pettigrew
Keyword(s):  
Stability Analysis ◽  
Force Field ◽  
Two Phase Flow ◽  
Tube Bundle ◽  
Mode Analysis ◽  
Phase Flow ◽  
Two Phase ◽  
Fluid Force ◽  
Flexible Tube ◽  
Fluidelastic Instability

Although almost half of the process heat exchangers operate in two-phase flow, the complex nature of the flow makes the prediction of fluidelastic instability a challenging problem yet to be solved. In the work reported here, the quasi-static fluid force-field is measured in a rotated-triangle tube bundle for a series of void fractions and flow velocities. The forces are strongly dependent on void fraction, flow rates and relative tube positions. The fluid force field is employed along with quasi-steady models [1, 2], originally developed for single phase flows, to model the two-phase flow problem. Stability analysis is performed using the single flexible tube model [1] as well as constrained mode analysis [2]. The results are compared with dynamic stability tests [3] and show good agreement. The results of single flexible tube analysis and multiple flexible tubes tend to coincide at low structural damping as expected. The present work uncovers some of the complexities of the fluid force field in two-phase flows. The data are valuable since they are the necessary inputs to the class of quasi-static, quasi-steady and quasi-unsteady fluidelastic instability theoretical models. This database opens a new research avenue on the feasibility of applying quasi-steady models to two-phase flow.

On the performance of a cascade of turbine rotor tip section blading in wet steam Part 3: Wake traverses

1997 ◽  
Vol 211 (8) ◽  
pp. 639-648 ◽  
Author(s):  
F Bakhtar ◽  
H Mashmoushy ◽  
O C Jadayel
Keyword(s):  
Liquid Phase ◽  
Two Phase Flow ◽  
Turbine Rotor ◽  
Phase Flow ◽  
Wet Steam ◽  
Flow Conditions ◽  
Two Phase ◽  
Blow Down ◽  
The Third ◽  
Phase Mixture

During the course of expansion of steam in turbines the fluid first supercools and then nucleates to become a two-phase mixture. The liquid phase consists of a large number of extremely small droplets which are difficult to generate except by nucleation. To reproduce turbine two-phase flow conditions requires a supply of supercooled vapour which can be achieved under blow-down conditions by the equipment employed. This paper is the third of a set describing an investigation into the performance of a cascade of rotor tip section profiles in wet steam and presents the results of the wake traverses.

Prediction of Pump Performance Under Air-Water Two-Phase Flow Based on a Bubbly Flow Model

1993 ◽  
Vol 115 (4) ◽  
pp. 781-783 ◽  
Author(s):  
Kiyoshi Minemura ◽  
Tomomi Uchiyama
Keyword(s):  
Two Phase Flow ◽  
Bubbly Flow ◽  
Phase Flow ◽  
Centrifugal Pumps ◽  
Flow Conditions ◽  
Two Phase ◽  
Performance Change ◽  
Void Fractions ◽  
Two Phases

This paper is concerned with the determination of the performance change in centrifugal pumps operating under two-phase flow conditions using the velocities and void fractions calculated under the assumption of an inviscid bubbly flow with slippage between the two phases. The estimated changes in the theoretical head are confirmed with experiments within the range of bubbly flow regime.

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