Aperiodic Instability of a Once-Through Steam Generator with a Feedwater Line

2006 ◽  
Author(s):  
Jae-Kwang Seo ◽  
Han-Ok Kang ◽  
Juhyeon Yoon ◽  
Keung-Koo Kim
Keyword(s):  
Experimental Data ◽  
Steam Generator ◽  
Pressure Difference ◽  
Flow Instability ◽  
Reverse Flow ◽  
Flow Direction ◽  
Minimum Pressure ◽  
Multiple Flows ◽  
Static Flow ◽  
Aperiodic Instability

Aperiodic (static) flow instability is an instability related to the change of a flow direction in individual steam generating U-shaped channels operating at given pressure difference. The nature of an aperiodic instability is close to a Ledinegg instability [1] related to the presence of multiple flows at the full hydraulic curve of a U-shaped channel. In this paper, the conditions for a reverse flow for a once-through steam generator (OTSG) with U-shaped modular feedwater line (MFL) are studied. From the results of the studies, it is revealed that the change of a flow direction in the MFL is due to the boiling of the feedwater in the downcomer branch of the U-shaped MFL and that multiple flows start in an area of the extremes corresponding to the minimum pressure difference of the hydraulic curves. Calculation models for predicting a threshold of an aperiodic instability for the OTSG of interest is proposed and the analysis results are compared with the experimental data.

Asymmetry Investigation on Single Phase Flow in Inverted U-Tubes of Steam Generator Under the Condition of Natural Circulation

2010 ◽  
Author(s):  
Chuan Wang ◽  
Lei Yu
Keyword(s):  
Experimental Data ◽  
Pressure Drop ◽  
Steam Generator ◽  
Mass Flux ◽  
Single Phase ◽  
Reverse Flow ◽  
Natural Circulation ◽  
Flow Characteristics ◽  
Operating Conditions ◽  
Outlet Temperature

In order to study the reverse flow characteristics in U-tubes of steam generator in the natural circulation case, the code RELAP5/MOD3.3 is used to model and calculate single-phase water flow for PWR under some typical operating conditions in the natural circulation case. The U-tubes of steam generator are classified according to their length and then are divided into different nodes and flow lines. The calculated results show that reverse flow exists in some inverted U-tubes of the steam generator, the natural circulation capacity of the primary coolant circuit system declines and the calculated net mass flux of the natural circulation accords with the experimental data. The traditional lumped parameter method can not simulate the reverse flow characteristics in inverted U-tubes and its result is much greater than the experimental data. When the steam generator outlet pressure is higher than inlet pressure, and gravitational pressure drop is lower than the total of frictional pressure drop and area change pressure drop, the reverse flow will occur. As to the nuclear power plant described in this paper, the mass flux of the shorter U-tubes drops more quickly and at last reverse flow will occur. The temperature distribution is uniform in inverted U-tubes, and it is almost identical with that of SG in secondary side. The occurrence of reverse flow can be judged by that whether the steam generator inlet temperature is lower than reactor outlet temperature obviously. It is indicated that reverse flow occurred in the U-tubes of the steam generator reduces the mass flux in the natural circulation system.

scholarly journals Effect of Heaving Movement on Flow Instability in U-Tubes of Marine Steam Generator under Natural Circulation

2013 ◽  
Vol 2013 ◽  
pp. 1-7 ◽  
Author(s):  
Jianli Hao ◽  
Wenzhen Chen ◽  
De Zhang
Keyword(s):  
Steam Generator ◽  
Single Phase ◽  
Flow Instability ◽  
Reverse Flow ◽  
Natural Circulation ◽  
Critical Mass ◽  
Space Distribution ◽  
Tube Length ◽  
One Dimensional ◽  
Acceleration Amplitude

Under heaving movement conditions, the single phase flow instability in U-tubes is affected by the additional force, which will influence the marine reactor operation. In the present work, one-dimensional thermal-hydraulic model in U-tubes under heaving movement conditions is established, and the critical pressure drop (CPD) and critical mass flow rate (CMFR) which relate to the occurrence of reverse flow in U-tubes are proposed and analyzed. The effects of the heaving period and heaving acceleration amplitude on the flow instability in U-tubes with the different length are discussed. It is shown that (1) the CPD and CMFR are obviously affected by the heaving movement, which means that the reverse flow characteristic in U-tubes will be changed; (2) the fluctuation periods of the CPD and CMFR are the same as the heaving period, but the fluctuation magnitude of them is little affected by the heaving period; (3) the relative changes of CPD and CMFR are the linear function of heaving acceleration amplitude; and (4) the U-tube length has little influence on the relative changes of CPD and CMFR compared with the heaving acceleration amplitude, which means that the heaving movement has little influence on the space distribution of reverse flow in the U-tubes of marine steam generator.

scholarly journals Movement of a finite body in channel flow

2016 ◽  
Vol 472 (2191) ◽  
pp. 20160164 ◽  
Author(s):  
Frank T. Smith ◽  
Edward R. Johnson
Keyword(s):  
Reynolds Number ◽  
Channel Flow ◽  
Flow Instability ◽  
Flow Direction ◽  
Finite Size ◽  
The Body ◽  
Thin Body ◽  
Shear Stresses ◽  
Unsteady Interaction ◽  
High Reynolds

A body of finite size is moving freely inside, and interacting with, a channel flow. The description of this unsteady interaction for a comparatively dense thin body moving slowly relative to flow at medium-to-high Reynolds number shows that an inviscid core problem with vorticity determines much, but not all, of the dominant response. It is found that the lift induced on a body of length comparable to the channel width leads to differences in flow direction upstream and downstream on the body scale which are smoothed out axially over a longer viscous length scale; the latter directly affects the change in flow directions. The change is such that in any symmetric incident flow the ratio of slopes is found to be cos ⁡ ( π / 7 ) , i.e. approximately 0.900969, independently of Reynolds number, wall shear stresses and velocity profile. The two axial scales determine the evolution of the body and the flow, always yielding instability. This unusual evolution and linear or nonlinear instability mechanism arise outside the conventional range of flow instability and are influenced substantially by the lateral positioning, length and axial velocity of the body.

Separation in oscillating laminar boundary-layer flows

1971 ◽  
Vol 47 (1) ◽  
pp. 21-31 ◽  
Author(s):  
R. A. Despard ◽  
J. A. Miller
Keyword(s):  
Experimental Data ◽  
Boundary Layer ◽  
Experimental Investigation ◽  
Reynolds Number ◽  
Reverse Flow ◽  
Oscillation Amplitude ◽  
Hot Wire ◽  
Boundary Layer Flows ◽  
Laminar Boundary Layers ◽  
History Of

The results of an experimental investigation of separation in oscillating laminar boundary layers is reported. Instantaneous velocity profiles obtained with multiple hot-wire anemometer arrays reveal that the onset of wake formation is preceded by the initial vanishing of shear at the wall, or reverse flow, throughout the entire cycle of oscillation. Correlation of the experimental data indicates that the frequency, Reynolds number and dynamic history of the boundary layer are the dominant parameters and oscillation amplitude has a negligible effect on separation-point displacement.

Compressor Performance 2D Modelling at Reverse Flow Conditions

2010 ◽  
Author(s):  
L. Gallar ◽  
I. Tzagarakis ◽  
V. Pachidis ◽  
R. Singh
Keyword(s):  
Experimental Data ◽  
Reverse Flow ◽  
Three Dimensional ◽  
Axial Compressor ◽  
Engine Performance ◽  
Two Dimensional ◽  
Flow Conditions ◽  
Compressor Surge ◽  
Compressor Performance ◽  
Shaft Failure

After a shaft failure the compression system of a gas turbine is likely to surge due to the heavy vibrations induced on the engine after the breakage. Unlike at any other conditions of operation, compressor surge during a shaft over-speed event is regarded as desirable as it limits the air flow across the engine and hence the power available to accelerate the free turbine. It is for this reason that the proper prediction of the engine performance during a shaft over-speed event claims for an accurate modelling of the compressor operation at reverse flow conditions. The present study investigates the ability of the existent two dimensional algorithms to simulate the compressor performance in backflow conditions. Results for a three stage axial compressor at reverse flow were produced and compared against stage by stage experimental data published by Gamache. The research shows that due to the strong radial fluxes present over the blades, two dimensional approaches are inadequate to provide satisfactory results. Three dimensional effects and inaccuracies are accounted for by the introduction of a correction parameter that is a measure of the pressure loss across the blades. Such parameter is tailored for rotors and stators and enables the satisfactory agreement between calculations and experiments in a stage by stage basis. The paper concludes with the comparison of the numerical results with the experimental data supplied by Day on a four stage axial compressor.

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.

Control of the Flow Direction Induced by Plasma Actuator

2012 ◽  
Author(s):  
Yu Ikoshi ◽  
Satoshi Ogata ◽  
Takehiko Segawa ◽  
Ryota Yamatani
Keyword(s):  
Applied Voltage ◽  
Reverse Flow ◽  
Flow Direction ◽  
Plasma Actuator ◽  
Lower Electrode ◽  
Barrier Discharge Plasma ◽  
Induced Flow ◽  
Piv Analysis ◽  
Asymmetric Electrodes ◽  
Aerodynamic Flow Control

It is known that a dielectric barrier discharge plasma actuator (DBD-PA) induces tangential flow in the vicinity of the wall. In the conventional studies the induced flow was generated in the direction from the upper electrode to the lower electrode. The direction of the induced flow was one-way using DBD-PA composed of asymmetric electrodes. However, in this experiment, it was found that the flow induced by DBD-PA can be generated in the opposite direction in contrast with conventional results. In this study, effects of DBD induced flow on applied voltage characteristics were investigated by means of PIV analysis. When square wave voltages biased negative are applied to the electrodes of DBD-PA, the flow is generated in the direction from the lower electrode to the upper electrode. It should be noted that it is not reversed by sine waves even with same amplitudes and frequencies when the reverse flow was generated by DBD-PA, a vortex is induced above the area of plasma. The vortex height was about 10 mm, and it tended to change slightly its shape based on the electrode width. It seems that the vortex on the plasma area play an important role in the mechanism of the reverse flow. The plasma actuator has been focused as an actuator for aerodynamic flow control. If it becomes possible to control the flow direction as well as the velocity by changing the applied voltage, the applications of the plasma actuator can be spread across a wide area of industry.

scholarly journals Numerical Prediction of Film Cooling Effectiveness and the Associated Aerodynamic Losses With a Three-Dimensional Calculation Procedure

1990 ◽  
Author(s):  
G. H. Dibelius ◽  
R. Pitt ◽  
B. Wen
Keyword(s):  
Experimental Data ◽  
Film Cooling ◽  
Reverse Flow ◽  
Turbine Blades ◽  
Three Dimensional ◽  
Temperature Pattern ◽  
Main Stream ◽  
Cooling Efficiency ◽  
Film Cooling Effectiveness ◽  
Aerodynamic Losses

Film cooling of turbine blades by injecting air through holes or slots affects the main stream flow. A numerical model has been developed to predict the resulting three-dimensional flow and the temperature pattern under steady flow conditions. An elliptic procedure is used in the near injection area to include reverse flow situations, while in the upstream area as well as far downstream a partial-parabolic procedure is applied. As first step an adiabatic wall has been assumed as boundary condition, since for this case experimental data are readily available for comparison. At elevated momentum blowing rates, zones of reverse flow occur downstream of the injection holes resulting in a decrease of cooling efficiency. A variation of the relevant parameters momentum blowing rate m, injection angle α and ratio of hole spacing to diameter s/d revealed the combination of m ≈ 1, α ≈ 30° and s/d ≈ 2 to be the optimum with respect to the averaged cooling efficiency and to the aerodynamic losses. Cooling is more efficient with slots than with a row of holes not considering the related problems of manufacture and service life. The calculated temperature patterns compare well with the experimental data available.

Studies on flow instability of helical tube steam generator with Nyquist criterion

2014 ◽  
Vol 266 ◽  
pp. 63-69 ◽  
Author(s):  
Fenglei Niu ◽  
Li Tian ◽  
Yu Yu ◽  
Rizhu Li ◽  
Timothy L. Norman
Keyword(s):  
Steam Generator ◽  
Flow Instability ◽  
Helical Tube ◽  
Nyquist Criterion

Experimental Study on the Avoidance and Suppression Criteria for the Vortex-Induced Vibration of a Cantilever Cylinder

2002 ◽  
Vol 124 (2) ◽  
pp. 187-195 ◽  
Author(s):  
Takaaki Sakai ◽  
Masaki Morishita ◽  
Koji Iwata ◽  
Seiji Kitamura
Keyword(s):  
Experimental Data ◽  
Experimental Study ◽  
Water Flow ◽  
Experimental Validation ◽  
Flow Direction ◽  
High Viscosity ◽  
Design Guideline ◽  
Vortex Induced Vibration ◽  
High Viscosity Oil ◽  
Effect Of Structure

Experimental validation of the design guideline to prevent the failure of a thermometer well by vortex-induced vibration is presented, clarifying the effect of structure damping on displacement amplitudes of a cantilever cylinder. The available experimental data in piping are limited to those with small damping in water flow, because of the difficulty in increasing structure damping of the cantilever cylinders in experiments. In the present experiment, high-viscosity oil within cylinders is used to control their structure damping. Resulting values of reduced damping Cn are 0.49, 0.96, 1.23, 1.98, and 2.22. The tip displacements of the cylinder induced by vortex vibration were measured in the range of reduced velocity Vr from 0.7 to 5 (Reynolds number is 7.8×104 at Vr=1). Cylinders with reduced damping 0.49 and 0.96 showed vortex-induced vibration in the flow direction in the Vr>1 region. However, in cases of reduced damping of 1.23, 1.98, and 2.22, the vibration was suppressed to less than 1 percent diameter. It is confirmed that the criteria of “Vr<3.3 and Cn>1.2” for the prevention of vortex-induced vibration is reasonably applicable to a cantilever cylinder in a water flow pipe.

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