Basic study on flow separation phenomenon in cooling system piping in fast reactors; Clarification of complex flow structure in a multi-elbow in a high Reynolds number regime (Joint research report in JFY2008 and JFY2009)

Ebara, Shinji*; Yuki, Kazuhisa*; Hashizume, Hidetoshi*; Aizawa, Kosuke; Yamano, Hidemasa

JAEA-Research 2013-011, 72 Pages, 2013/10

JAEA-Research-2013-011.pdf:11.34MB

In Tohoku University, different scale model experiments were carried out in order to clarify unsteady flow fields and pressure fluctuation characteristics in the cold leg piping by means of visualization experiment and pressure measurement, respectively, and to investigate the scale effect. In JFY2008, the visualization experiment by PIV measurement for the 1/15 scale piping was carried out using a double elbow geometry. Besides, shakedown tests of the 1/7 scale model were conducted for the case of a single elbow. In JFY2009, visualization experiments for the 1/7 scale models with the single and a three-dimensionally connected double elbow geometries were carried out. From these obtained data, effects of the multiple elbows on the flow field were assessed. In addition, the pressure measurements for single elbow flows by using 1/15 and 1/7 scale models were performed. In JAEA, numerical analyses for the 1/7 scale double elbow experiments were performed using the commercial thermal-hydraulics code STAR-CD. The analyses showed that the calculated velocity distributions were in good agreement with the visualization experimental results. It was confirmed, from these analyses, that the URANS analysis method validated for the single elbow flow has applicability to the double elbow flow.

Matched refractive-index PIV visualization of complex flow structure in a three-dimentionally connected dual elbow

Yuki, Kazuhisa*; Hasegawa, Shunsuke*; Sato, Tsukasa*; Hashizume, Hidetoshi*; Aizawa, Kosuke; Yamano, Hidemasa

Nuclear Engineering and Design, 241(11), p.4544 - 4550, 2011/11

https://doi.org/10.1016/j.nucengdes.2010.12.026

Pressure fluctuation characteristics of complex turbulent flow in a single elbow with small curvature radius for a sodium-cooled fast reactor

Ebara, Shinji*; Aoya, Yuta*; Sato, Tsukasa*; Hashizume, Hidetoshi*; Yuki, Kazuhisa*; Aizawa, Kosuke; Yamano, Hidemasa

Journal of Fluids Engineering, 132(11), p.111102_1 - 111102_7, 2010/11

https://doi.org/10.1115/1.4002813

A multi-elbow piping system is adopted for the Japan Sodium-cooled Fast Reactor (JSFR) cold-legs. Flow Induced Vibration (FIV) is considered to appear due to complex turbulent flow with very high Reynolds number in the piping. In this study, pressure measurement for a single elbow flow is conducted to elucidate pressure fluctuation characteristics originated from turbulent motion in the elbow, which lead potentially to the FIV. Two different scale models, 1/7 and 1/14-scale simulating the JSFR cold-leg piping, are tested experimentally to confirm whether a scale effect in pressure fluctuation characteristics exists. A distinguishing peak can be seen in each power spectrum density (PSD) profile of pressure fluctuation obtained in and downstream of the flow separation region for both scaled models. When nondimensionalized, the PSD profiles show good correspondence regardless of scale model and even of Reynolds number simulated in this study.

Unsteady hydraulic characteristics in large-diameter pipings with elbow for JSFR, 3; Flow structure in a 3-dimentionally connected dual elbow simulating cold-leg piping in JSFR

Yuki, Kazuhisa*; Hasegawa, Shunsuke*; Sato, Tsukasa*; Hashizume, Hidetoshi*; Aizawa, Kosuke; Yamano, Hidemasa

Proceedings of 13th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-13) (CD-ROM), 11 Pages, 2009/09

In this study, the flow structures in a 3-dimentionally connected dual elbow, which simulates a part of the cold leg, are visualized by PIV measurement, and it is discussed on the detailed flow transition from the 1st elbow to the 2nd elbow and the generation of unsteady flow such as a separation that influences flow-induced vibration. Experimental apparatus has a 1/15 scale test section of actual design whose inner diameter and curvature radius ratio are 56mm and 1.0, respectively. For visualization without any image distortion, matched refractive-index PIV measurement is carried out using NaI solution as the working fluid. The Reynolds number is 50,000, and the inlet flow condition to the test section is a fully developed turbulent flow. It is confirmed that it generates a separation along the inner wall of the 1st elbow and one large swirling flow in the 2nd elbow. Furthermore, unsteady flow formed in and/or behind the separation region is transported downstream and flows into the center area of the 2nd elbow.

Suppression of high-cycle thermal fatigue at a mixing tee with a 90-degree bend upstream by changing its geometry

Yuki, Kazuhisa*; Ohara, Hiroshi*; Hashizume, Hidetoshi*; Tanaka, Masaaki; Muramatsu, Toshiharu; Toda, Saburo*

Proceedings of 7th International Topical Meeting on Nuclear Reactor Thermal Hydraulics, Operation and Safety (NUTHOS-7) (CD-ROM), 21 Pages, 2008/10

Velocity measurement by PIV (Particle Image Velocimetry) and measurement of fluid-temperature are conducted in a mixing tee with an elbow on the upstream side of the tee. Parameters in the experiment are the distance between the elbow pipe exit and the tee and the curvature radius of the elbow pipe. By the experiment, certain suppression techniques for high cycle thermal fatigue in the mixing tee area are proposed to control the distance between the elbow and the tee according to the curvature radius of the elbow.

Control technique of high-cycle thermal fatigue at a mixing tee with a 90-degree bend upstream by changing its location

Ohara, Hiroshi*; Yuki, Kazuhisa*; Hoseini, S. M.*; Hashizume, Hidetoshi*; Tanaka, Masaaki

Proceedings of 15th International Conference on Nuclear Engineering (ICONE-15) (CD-ROM), 10 Pages, 2007/04

When temperature fluctuation in mixing tee pipe is transported to the structure, it may lead high-cycle thermal fatigue in the structure. Therefore, it is important to control the high-cycle thermal fatigue. In a 90-degree bend located in upstream of the tee, an unsteady secondary flow arises. The secondary flow affects the fluid mixing in tee and the distance between the tee and the bend is one of the most important parameters to characterize the temperature fluctuation. The temperature fluctuation and the fluid mixing structure are investigated experimentally varied the distance between the tee and the bend. When the tee is located at the close to the bend, the fluid mixing area tends to shift to the inside of the bended pipe. And the temperature fluctuation intensity becomes lower and decays faster in the stream direction. Experimental results suggest that changing the distance between the tee and the bend is useful to control the high-cycle thermal fatigue.

Investigation of thermal hydraulic mixing mechanism in T-junction pipe with a 90-degree bend in upstream side for mitigation and controlling of thermal-striping phenomena (Joint research)

Yuki, Kazuhisa*; Hashizume, Hidetoshi*; Tanaka, Masaaki; Muramatsu, Toshiharu

JAEA-Research 2006-025, 47 Pages, 2006/03

JAEA-Research-2006-025.pdf:4.26MB

In T-junction pipe, temperature fluctuation is induced due to unstable fluid mixing. Development of the relaxation and control techniques for the thermal fatigue is one of the most important issues in the future plant design. If a 90-degree bend exists in the upstream of the mixing tee in the piping system of power plants, a secondary flow formed in the bend makes the fluid mixing phenomena even more complex. This study aims at clarifying effects of curvature ratio of the bend on the non-isothermal fluid mixing in the Tee-junction area and the temperature fluctuation induced by the unstable mixing, by visualizing the flow fields with PIV and measuring fluid-temperature fluctuation in the vicinity of wall. From the visualization, it is clarified that a high-temperature jet flowing out from a branch pipe swings and sways near the wall, which leads to higher temperature fluctuation than that in a case without the 90-degree bend. In addition, in the case that there exists a separation in the bend, the fluid mixing and the temperature fluctuation characteristics including its damping in the downstream direction are completely different from those without the separation. Furthermore, in the case using the bend that doesn't produce the separation, there are cautionary conditions in which the temperature fluctuation is maximized in a transition regime of a stratified flow and a turn-jet flow. It seems that the principal cause for this is repetition generation and disappearance of a circulating flow formed behind the jet due to an interaction between unsteady behavior of a secondary flow in a decay process after the bend and the wakes formed behind the jet, which leads to the vigorous oscillation of jet near the wall. For the prediction of the temperature fluctuation, it's possible to predict it in each fluid mixing pattern.

Elucidation of Thermal Hydraulic Mixing Mechanism in a Mixing Tee Area with a 90-degree Bend Upstream and Development of Thermal-striping Relaxation and Control Methods

Sugawara, Yoshimasa*; Yuki, Kazuhisa*; Hashizume, Hidetoshi*; Tanaka, Masaaki; Muramatsu, Toshiharu

JNC TY9400 2004-027, 65 Pages, 2004/10

JNC-TY9400-2004-027.pdf:12.54MB

In this study, non-isothermal fluid mixing experiments in a T-junction area with a 90-degree bend upstream were carried out to estimate the fluid-temperature fluctuation in the vicinity of wall. The temperature fluctuations for various flow mixing conditions were measured, changing a velocity ratio and a pipe diameter ratio of a main pipe to a branch pipe to quantitatively evaluate the effect of a secondary flow on the temperature fluctuation. In addition, by analyzing both the visualization data taken by a PIV system and the temperature fluctuation data, it was attempted to construct a prediction formula for the temperature fluctuation.

Study on flow-induced-vibration evaluation of large-diameter pipings in a sodium-cooled fast reactor,6; PIV visualization on complex flow field in a cold-leg multi-elbow to a scale of 1/15

Yoshida, Kazuhiro*; Yuki, Kazuhisa*; Sato, Tsukasa*; Hashizume, Hidetoshi*; Yamano, Hidemasa; Kotake, Shoji

no journal, , 

Flow dynamics in an elbow pipe has been observed by a PIV flow visualization experiments with a 1/15 scale test facility simulating a cold-leg piping in a sodium-cooled fast reactor. This paper also reports the overview of the facility of an upcoming 1/7 scale test and its plan.

Study on flow-induced-vibration evaluation of large-diameter pipings in a sodium-cooled fast reactor, 18; PIV visualization of single elbow flow with Re=10

Sato, Tsukasa*; Ebara, Shinji*; Hashizume, Hidetoshi*; Yusa, Noritaka*; Yuki, Kazuhisa*; Aizawa, Kosuke; Yamano, Hidemasa

no journal, , 

To clarify a flow pattern in a multiple elbow pipe of cold-leg in sodium-cooled fast reactor, the 1/7 scale flow experiment was performed as the first step to measure the flow velocity distribution in a single elbow pipe under Re=110 by using the PIV technique.

Study on flow-induced-vibration evaluation of large-diameter pipings in a sodium-cooled fast reactor, 24; PIV measurement for dual elbow flow using 1/7-scale model of cold-leg piping

Ebara, Shinji*; Hashizume, Hidetoshi*; Yuki, Kazuhisa*; Aizawa, Kosuke; Yamano, Hidemasa

no journal, , 

Experiment on flow in a dual elbow has been conducted to clarify the complex flow behavior, using a 1/7-scale model of cold-leg piping of a sodium-cooled fast reactor. Several cases of elbow effects have been examined by using PIV measurement to evaluate flow fields which have strong unsteadiness and resultant effect on flow-induced vibration, e.g. separation vortex in a range of high Reynolds numbers, and also by comparing the result with that of a single elbow.