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論文

Simulation of a jet flow rectified by a grating-type structure using immersed boundary methods

廣瀬 意育; 安部 諭; 石垣 将宏*; 柴本 泰照; 日引 俊*

Progress in Nuclear Energy, 169, p.105085_1 - 105085_13, 2024/04

Immersed boundary methods (IBMs) have been developed as complementary methods for computational fluid dynamics (CFD). They allow a flow simulation in a mock-up model that includes complex-shaped inner structures and/or boundaries with a non-body conformal mesh. Such a model might force us to create a complicated body-fitted mesh with a high cost in the conventional CFD (CCFD) approach. We focus on the Brinkman penalization (BP) method and its extended version, which we call here the extended Brinkman penalization method (EBP), among the different types of IBMs, aiming to apply them to the phenomena that occur during severe accidents in a nuclear reactor containment vessel and explore the possibility that the methods can partially replace the CCFD. In this paper, as a preliminary step to validate the applicability of these methods, we measure the jet flow rectified by a grating-type structure used for the validation of numerical techniques and apply them to simulate the behavior of an upward jet rectified by a horizontally placed grating-type structure modeled as an immersed body. This type of structure is generally used in reactor buildings, and it is crucial to evaluate their influence on gaseous flows because the behaviors of hydrogen produced during severe accidents may be influenced by them. The structure is selected as our subject because it has moderate complexity, enabling us to examine the effects of the IBMs and compare them with CCFD. We investigate whether these methods can reproduce a result of corresponding CCFD in which the grating is modeled as body-conformal mesh and show that the former can produce the latter with equivalent accuracy. All these results are also compared with the experimental data on the flow velocity distributions downstream of the grating measured using particle image velocimetry.

論文

Application of analytical wall functions to CFD analysis of condensation flow

相馬 秀; 石垣 将宏*; 安部 諭; 柴本 泰照

Nuclear Engineering and Design, 416, p.112754_1 - 112754_18, 2024/01

The wall function (WF) enables analyzing condensation flow in a nuclear reactor containment vessel with reasonable computational costs. However, conventional wall treatments rely on the logarithmic laws for velocity, temperature, and concentration, limiting applicability. In this paper, we applied the analytical wall function approach to the condensation flow analysis of steam/air mixtures. This approach features the analytical integration of transport equations considering the buoyancy, the material property change, and the convective terms. We conducted CFD analysis with the analytical wall function models for the forced, mixed, and natural convection and confirmed good prediction, especially when the log law does not hold.

論文

Boundary layer measurements for validating CFD condensation model and analysis based on heat and mass transfer analogy in laminar flow condition

相馬 秀; 石垣 将宏*; 安部 諭; 柴本 泰照

Nuclear Engineering and Technology, 10 Pages, 2024/00

When analyzing containment thermal-hydraulics, computational fluid dynamics (CFD) is a powerful tool because multi-dimensional and local analysis is required for some accident scenarios. According to the previous study, neglecting steam bulk condensation in the CFD analysis leads to a significant error in boundary layer profiles. Validating the condensation model requires the experimental data near the condensing surface, however, available boundary layer data is quite limited. It is also important to confirm whether the heat and mass transfer analogy (HMTA) is still valid in the presence of bulk condensation. In this study, the boundary layer measurements on the vertical condensing surface in the presence of air were performed with the rectangular channel facility WINCS, which was designed to measure the velocity, temperature, and concentration boundary layers. We set the laminar flow condition and varied the Richardson number (1.0-23) and the steam volume fraction (0.35-0.57). The experimental results were used to validate CFD analysis and HMTA models. For the former, we implemented a bulk condensation model assuming local thermal equilibrium into the CFD code and confirmed its validity. For the latter, we validated the HMTA-based correlations, confirming that the mixed convection correlation reasonably predicted the sum of wall and bulk condensation rates.

論文

CFD analysis on stratification dissolution and breakup of the air-helium gas mixture by natural convection in a large-scale enclosed vessel

Hamdani, A.; 安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Progress in Nuclear Energy, 153, p.104415_1 - 104415_16, 2022/11

 被引用回数:3 パーセンタイル:71.05(Nuclear Science & Technology)

This paper describes the computational fluid dynamics (CFD) analysis and validation works from the previous experimental study on the natural convection driven by outer surface cooling in the presence of density stratification consisting of air and helium (as a mimic gas of hydrogen). The experiment was conducted in the Containment InteGral effects Measurement Apparatus (CIGMA) facility at Japan Atomic Energy Agency (JAEA). The numerical simulation was carried out to analyze the detailed effect of the cooling region on the erosion of the helium stratification layer. The temporal and spatial evolution of the helium concentration and the gas temperature inside the containment vessel was predicted and validated against the experimental data. In addition, two stratification behaviors that depend on the cooling location were presented and discussed. The CFD simulation confirmed that an upper head cooling caused two counter-rotating vortexes in the helium-rich zone. Meanwhile, the upper half body cooling caused two counter-rotating vortexes in the helium-poor zone. These findings are important to understand the mechanism of the density stratification process driven by natural convection in the containment vessel.

論文

Estimation of flow field in natural convection with density stratification by local ensemble transform Kalman filter

石垣 将宏*; 廣瀬 意育; 安部 諭; 永井 亨*; 渡辺 正*

Fluids (Internet), 7(7), p.237_1 - 237_18, 2022/07

To estimate thermal flow in a nuclear reactor during an accident, it is important to improve the accuracy of computational fluid dynamics simulation. Temperature and flow velocity are not homogeneous and have large variations in a reactor containment vessel because of its very large volume. In addition, Kelm et al (2016) pointed out that the influence of variations of initial and boundary conditions was important. Therefore, it is necessary to set the initial and boundary conditions taking into account the variations of these physical quantities. However, it is a difficult subject to set such complicated initial and boundary conditions. Then, we can obtain realistic initial and boundary conditions by the data assimilation technique, and we can improve the accuracy of the simulation result. In this study, we applied the data assimilation by local ensemble transform Kalman filter (Hunt et al., 2007) to the simulation of natural convection behavior in density stratification, and we performed a twin model experiment. We succeeded in the estimation of the flow fields and improving the simulation accuracy by the data assimilation, even if we applied the boundary condition with error for the true condition.

論文

Numerical analysis of natural convection behavior in density stratification induced by external cooling of a containment vessel

石垣 将宏*; 安部 諭; Hamdani, A.; 廣瀬 意育

Annals of Nuclear Energy, 168, p.108867_1 - 108867_20, 2022/04

 被引用回数:3 パーセンタイル:71.05(Nuclear Science & Technology)

It is essential to improve computational fluid dynamics (CFD) analysis accuracy to estimate thermal flow in a containment vessel during a severe accident. Previous studies pointed out the importance of the influence of initial and boundary conditions on the CFD analysis. The purpose of this study is to evaluate the influence of initial and boundary conditions by numerical analysis of natural convection experiments in a large containment vessel test facility CIGMA(Containment InteGral effects Measurement Apparatus). A density stratification layer was initially formed in the vessel using helium and air, and external cooling of the vessel surface-induced natural convection. In this study, we carried out numerical simulations of the density stratification erosion driven by the natural convection using the RANS (Reynolds averaged Navier-Stokes) model. As a result, the temperature boundary condition of the small internal structure in the vessel had a significant influence on the fluid temperature distribution in the vessel. The erosion velocity of the density stratification layer changed depending on the initial gas concentration distribution. Then, appropriate settings of the temperature and gas concentration conditions are necessary for accurate analysis.

論文

Measurement of velocity and temperature profiles in boundary layer with steam condensation

相馬 秀; 安部 諭; 柴本 泰照; 石垣 将宏*

Proceedings of 19th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-19) (Internet), 13 Pages, 2022/03

The experimental data of boundary layer profiles are necessary to validate condensation models applied in numerical simulation of CFD codes and also to develop wall treatment models for heat and mass transfer in the presence of significant buoyancy and suction. The available data for velocity, temperature, and concentration boundary layer, however, is quite limited. In this study, we present experimental results of measuring boundary layer profiles by our experimental facility WINCS (WINd tunnel for Condensation of Steam and air mixture). WINCS is a once-through type of wind tunnel having a 1.5m-long measuring part of rectangular duct. The velocity and temperature profiles were obtained with laser doppler velocimetry and thermocouple, respectively. The temperature data was then used to calculate the steam concentration boundary layer by assuming local thermodynamic equilibrium. The laminar boundary layer profiles were obtained in the present condition. The dropwise condensation and fimwise condensation are available in this apparatus. We also conducted numerical simulations with CFD codes and compared the experimental and numerical results of boundary layer profiles and heat fluxes. The wall condensation model based on Stefan flow and bulk condensation model were used in the numerical analysis. The comparison, in general, shows good agreement between the experimental and numerical results.

論文

Experimental investigation of natural convection and gas mixing behaviors driven by outer surface cooling with and without density stratification consisting of an air-helium gas mixture in a large-scale enclosed vessel

安部 諭; Hamdani, A.; 石垣 将宏*; 柴本 泰照

Annals of Nuclear Energy, 166, p.108791_1 - 108791_18, 2022/02

 被引用回数:4 パーセンタイル:58.27(Nuclear Science & Technology)

This paper describes an experimental investigation of natural convection driven by outer surface cooling in the presence of density stratification consisting of an air-helium gas mixture (as mimic gas of hydrogen) in an enclosed vessel. The unique cooling system of the Containment InteGral effects Measurement Apparatus (whose test vessel is a cylinder with 2.5-m diameter and 11-m height) is used, and findings reveal that the cooling location relative to the stratification plays an important role in determining the interaction behavior of the heat and mass transfer in the enclosed vessel. When the cooling region is narrower than the stratification thickness, the density-stratified region expands to the lower part while decreasing in concentration (stratification dissolution). When the cooling region is wider than the stratification thickness, the stratification is gradually eroded from the bottom with decreasing layer thickness (stratification breakup). This knowledge is useful for understanding the interaction behavior of heat and mass transfer during severe accidents in nuclear power plants.

論文

Numerical study on an interface compression method for the volume of fluid approach

岡垣 百合亜; 与能本 泰介; 石垣 将宏; 廣瀬 意育

Fluids (Internet), 6(2), p.80_1 - 80_17, 2021/02

Many thermohydraulic issues about the safety of light water reactors are related to complicated two-phase flow phenomena. In these phenomena, computational fluid dynamics (CFD) analysis using the volume of fluid (VOF) method causes numerical diffusion generated by the first-order upwind scheme used in the convection term of the volume fraction equation. Thus, in this study, we focused on an interface compression (IC) method for such a VOF approach; this technique prevents numerical diffusion issues and maintains boundedness and conservation with negative diffusion. First, on a sufficiently high mesh resolution and without the IC method, the validation process was considered by comparing the amplitude growth of the interfacial wave between a two-dimensional gas sheet and a quiescent liquid using the linear theory. The disturbance growth rates were consistent with the linear theory, and the validation process was considered appropriate. Then, this validation process confirmed the effects of the IC method on numerical diffusion, and we derived the optimum value of the IC coefficient, which is the parameter that controls the numerical diffusion.

論文

Density stratification breakup by a vertical jet; Experimental and numerical investigation on the effect of dynamic change of turbulent Schmidt number

安部 諭; Studer, E.*; 石垣 将宏; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 368, p.110785_1 - 110785_14, 2020/11

 被引用回数:7 パーセンタイル:72.51(Nuclear Science & Technology)

The hydrogen behavior in a nuclear containment vessel is one of the significant issues raised when discussing the potential of hydrogen combustion during a severe accident. Computational Fluid Dynamics (CFD) is a powerful tool for better understanding the turbulence transport behavior of a gas mixture, including hydrogen. Reynolds-averaged Navier-Stokes (RANS) is a practical-use approach for simulating the averaged gaseous behavior in a large and complicated geometry, such as a nuclear containment vessel; however, some improvements are required. We implemented the dynamic modeling for $$Sc_{t}$$ based on the previous studies into the OpenFOAM ver 2.3.1 package. The experimental data obtained by using a small scale test apparatus at Japan Atomic Energy Agency (JAEA) was used to validate the RANS methodology. Moreover, Large-Eddy Simulation (LES) was performed to phenomenologically discuss the interaction behavior. The comparison study indicated that the turbulence production ratio by shear stress and buoyancy force predicted by the RANS with the dynamic modeling for $$Sc_{t}$$ was a better agreement with the LES result, and the gradual decay of the turbulence fluctuation in the stratification was predicted accurately. The time transient of the helium molar fraction in the case with the dynamic modeling was very closed to the VIMES experimental data. The improvement on the RANS accuracy was produced by the accurate prediction of the turbulent mixing region, which was explained with the turbulent helium mass flux in the interaction region. Moreover, the parametric study on the jet velocity indicates the good performance of the RANS with the dynamic modeling for $$Sc_{t}$$ on the slower erosive process. This study concludes that the dynamic modeling for $$Sc_{t}$$ is a useful and practical approach to improve the prediction accuracy.

論文

LES-WALE simulation on two liquid mixing in the horizontal legs and downcomer; The Open-test condition in the TAMU-CFD benchmark (IBE-5)

安部 諭; 岡垣 百合亜; 石垣 将宏; 柴本 泰照

Proceedings of OECD/NEA Workshop on Virtual CFD4NRS-8; Computational Fluid Dynamics for Nuclear Reactor Safety (Internet), 11 Pages, 2020/11

The fifth international benchmark exercise (IBE-5), the cold-leg mixing CFD benchmark, was conducted under the support of OECD/NEA. The experiment for IBE-5 was designed to visualize the mixing phenomena of two liquids with different density in a horizontal leg (as a simulant of the cold-leg) and downcomer. This paper shows our CFD result on the open test condition in IBE-5. We selected the Large-eddy simulation (LES) solving the filtered equation of flow and concentration fields. Regarding the eddy-viscosity to model the turbulence flux of the momentum at sub-grid scale (SGS), Wall-adapting locale eddy-viscosity (WALE) model, a modified version from the Smagorinsky model, was applied. The experimental geometry was resolved with three different numerical mesh systems. The CFD analysis predicted the laminar-like flow behavior in the horizontal leg. Due to the large density difference between the two liquids, the turbulence production was suppressed strongly, and the velocity fluctuation in the horizontal leg became very slow and small. In contrast, the strong turbulence mixing in the downcomer was predicted. The plume from the horizontal leg entrained with the surroundings and spread circumferentially in the downcomer. The comparison with the TAMU experimental data reveals the good performance of the WALE model. In addition, we discuss the appearance characteristics of the high concentration of the heavy liquid in the downcomer in the LES. The Probability Density Function (PDF) and Cumulative Distribution Function (CDF) are derived based on the predicted time-series of the heavy liquid concentration. The PDF around the mean concentration in the case with the low mesh resolution is larger than that predicted by the higher resolution due to the excessive homogenization of the heavy fluid concentration. This study reveals the importance to note the required mesh resolution to predict the appearance event of the high concentration.

論文

Experimental investigation of density stratification behavior during outer surface cooling of a containment vessel with the CIGMA facility

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Nuclear Engineering and Design, 367, p.110790_1 - 110790_15, 2020/10

 被引用回数:11 パーセンタイル:82.73(Nuclear Science & Technology)

シビアアクシデント時の格納容器(CV)内の流体や構造物を冷却するための有効なアクシデントマネジメントとして、CVの外面冷却が期待されている。一方、以下のような可能性も考えられる。第一に、シビアアクシデント時に水-ジルコニウム反応により水素ガスが発生し、外表面冷却により水素を含む非凝縮性ガスが蓄積し、密度成層が形成される可能性がある。第二に、非凝縮性ガスの蓄積は熱伝達を低下させ、CVの冷却を阻害する可能性がある。これらの課題については、これまで多くの研究が行われてきた。しかし、外表面冷却によって生じる密度成層挙動や成層崩壊の条件に着目した体系的な検討は十分に行われていない。また、水素の蓄積による伝熱劣化を定量的に評価していない。そこで、実験設備CIGMA(Containment InteGral effects Measurement Apparatus)を構築し、CIGMA設備を用いて容器外面冷却時の格納容器熱流動挙動の実験的研究を行った。さらに、安定な密度成層が維持できる条件を考慮することで、自然対流が密度成層化挙動に与える影響を議論した。

論文

Application of immersed boundary method for jet flow in grating type structure

廣瀬 意育; 石垣 将宏; 安部 諭; 柴本 泰照

Proceedings of International Topical Meeting on Advances in Thermal Hydraulics (ATH '20) (Internet), p.757 - 767, 2020/10

This paper describes an application of an immersed boundary method (IBM) to internal structure in a containment vessel as a means to reduce the modeling cost for accident analysis. A brinkman penalization method, that is one of the IBMs, is selected and implemented in OpenFOAM code. The calculation is performed for a grating-type structure in a rectangular vessel and an upward jet flow impinging on the grating is analyzed. The IBM is an appealing approach for solving flow passing complex geometry, whereas a very complicated body fitted mesh with fine resolution might be required in a conventional CFD approach. The results were compared with experimental data of flow velocity distribution through the grating measured by Particle Image Velocimetry technique. The flow immediately downstream of the grating is characterized by multimodal profile with intervals determined by a lattice width of the grating. This multimodal flow merges into one with unimodal shape in the downstream far from the grating. The present analysis reproduced the distinctive flow structure observed in the experiment. The model predicted a serrated profile consistent with the experimental results and this could be reproduced even with a relatively regular computational mesh compared to the traditional method.

論文

Unsteady natural convection in a cylindrical containment vessel (CIGMA) with external wall cooling; Numerical CFD simulation

Hamdani, A.; 安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Energies (Internet), 13(14), p.3652_1 - 3652_22, 2020/07

 被引用回数:4 パーセンタイル:19.33(Energy & Fuels)

In the case of a severe accident, natural convection plays an important role in the atmosphere mixing of nuclear reactor containments. In this case, the natural convection might not in the steady-state condition. Hence, instead of steady-state simulation, the transient simulation should be performed to understand natural convection in the accident scenario within a nuclear reactor containment. The present study, therefore, was aimed at the transient 3-D numerical simulations of natural convection of air around a cylindrical containment with unsteady thermal boundary conditions (BCs) at the vessel wall. For this purpose, the experiment series was done in the CIGMA facility at Japan Atomic Energy Agency (JAEA). A 3-D model was simulated with OpenFOAM, applying the unsteady Reynolds-averaged Navier-Stokes equations (URANS) model. Different turbulence models were studied, such as the standard k-$$varepsilon$$, standard k-$$omega$$, k-$$omega$$ shear stress transport (SST), and low-Reynolds-k-$$varepsilon$$ Launder-Sharma. The results of the four turbulence models were compared versus the results of experimental data.

論文

CFD analysis of the CIGMA experiments on the heated JET injection into containment vessel with external surface cooling

Hamdani, A.; 安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.5463 - 5479, 2019/08

The present study introduces thermal mixing and stratification produced by heated air jet located at the bottom level of the containment vessel. The investigation was carried out experimentally and numerically in the large containment vessel called CIGMA (Containment InteGral effects Measurement Apparatus). The experiments were conducted with external surface cooling and various air jet inlet temperatures. The containment cooling was done by flooding the water on the external side of half-upper of a vessel. To identify their influence on the thermal mixing and stratification phenomena, the investigation focuses on mixing convection which occurred in the cooled region of a containment vessel. Temperature distribution and jet velocity were measured by thermocouple and Particle Image Velocimetry (PIV) respectively. Numerical simulation was performed using Computational Fluid Dynamics (CFD) code OpenFOAM to investigate the detail effects of external cooling on the fluid flow and thermal characteristics in the test vessel. CFD results showed a good agreement with experimental data on both temperature and velocity. Both temperature and velocity of hot air jet decayed rapidly downstream jet nozzle. Thermal stratification was observed by visualization of temperature contour maps over a cross-section in the containment vessel. Vigorous mixing was also noticed in the upper region of the containment vessel. Effect of external cooling on mixing and the thermal stratification were presented and discussed.

論文

Experiment on density stratification behavior by containment venting using CIGMA Facility

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 18th International Topical Meeting on Nuclear Reactor Thermal Hydraulics (NURETH-18) (USB Flash Drive), p.5927 - 5940, 2019/08

格納容器ベントシステムはシビアアクシデント時における格納容器の過圧を防止するための手段として適用される。ベント時に発生する現象の理解と最適な運用という観点から、格納容器ベント時の水素挙動に関する研究は十分ではない。そこで本研究では大型格納容器実験装置CIGMAを用いて格納容器ベントに関する基礎的な実験を実施した。特に、ベントによる水素輸送に対するベント流量及び初期ガス分布の影響について調査を行った。水素の代替ガスであるヘリウム,蒸気,空気を用いて、初期に容器内に成層を形成し、下部ベントラインからベントを実施した。ベントにより初期に容器下部に存在する蒸気・空気のみが排出され、ヘリウム成層が下方へと拡大していく挙動が観察された。この間、上部のヘリウム濃度は一定であった。最終的には容器内のガス濃度分布は均質化した。今回実施した実験条件では、ベントによる容器内のガスの顕著な混合は観察されなかった。また異なる初期濃度分布に対してもヘリウム成層の挙動に大きな差は見られなかった。

論文

Numerical simulation of natural circulation experiment under asymmetric cooldown using LSTF

石垣 将宏; 渡辺 正*

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 10 Pages, 2018/10

2011年にOECD/ROSA-2プロジェクトの一環として自然循環実験を行った。事故時において蒸気発生器(SG)の2次側の冷却材を喪失した場合、異常側SGにおける循環が停止する可能性がある。実験では片側SGの2次側を空にし、健全側SGの2次側を階段状に減圧した際の自然循環挙動の計測を行った。本研究ではこのLSTFによる自然循環実験をTRACEコードにより解析を実施した。解析の結果、健全側ループの循環流量は実験よりもわずかに過小評価し、異常側ループの流量を過大評価した。さらに冷却率に対する自然循環挙動の感度解析も実施した。

論文

Experiments on collapse of density stratification by outer surface cooling of containment vessel; CC-PL-12 and CC-PL-24 experiments at CIGMA

石垣 将宏; 安部 諭; 柴本 泰照; 与能本 泰介

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 11 Pages, 2018/10

シビアアクシデント時における格納容器内熱水力挙動は安全上重要な課題の1つである。本研究では大型格納容器実験装置CIGMAを用いて、格納容器内の水素挙動および自然循環挙動に対する格納容器を外部から冷却した際の影響について検討した。本実験では2つの冷却手法を適用した実験を行った。1つは上部プールに蓄えた冷却水による冷却と上部プール・中段ジャケットへの流下液膜による冷却である。容器内に水素の模擬物質としてヘリウムを注入し、さらに蒸気と空気を注入し、容器上部にヘリウム成層を形成した際の成層挙動について計測を行った。冷却手法に応じて、異なる成層挙動が観測された。

論文

Analyses of LSTF experiment and PWR plant for 5% cold-leg break loss of coolant accident

渡辺 正*; 石垣 将宏*; 勝山 仁哉

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 9 Pages, 2018/10

LSTF及びPWRプラントに対する5%コールドレグ破断による冷却材喪失事故について、これらを対象とした解析モデルを整備し、RELAP5/MOD3.3コードを用いて解析を行った。臨界流モデルの放出係数は、LSTFに対する実験と解析の圧力過渡が一致するよう決定し、PWR解析にも適用した。その結果、解析結果は、LSTF実験に対する熱水力学的挙動をよく再現できることを示した。しかしながら、ループシールよる炉心における差圧の減少やループ流速は過小評価された。また、LSTF実験に対する解析ではボイルオフ中における炉心の加熱時間は長いものの、LSTFとPWRプラント間ではそれらはよく一致することから、スケーリング効果は小さいことも明らかとなった。

論文

Influence of grating type obstacle on stratification breakup by a vertical jet

安部 諭; 石垣 将宏; 柴本 泰照; 与能本 泰介

Proceedings of 12th International Topical Meeting on Nuclear Reactor Thermal-Hydraulics, Operation and Safety (NUTHOS-12) (USB Flash Drive), 9 Pages, 2018/10

At Japan Atomic Energy Agency (JAEA), small scale experiment, named VIMES (VIsualization and MEasurement system on stratification behavior) experiment, has been performed since 2014. In this paper, we introduce the influence of grating type obstacle to the VIMES experiment. Two types of grating obstacle were constructed based on the aperture area ratio. The obstacles were placed at the intermediate position between the jet nozzle exit and bottom of the initial stratification. Experimental results showed that the vertical jet was strongly affected by the grating obstacle. Due to the rectifying effect, the radial spreading was suppressed and the velocity magnitude on the jet center line became larger than that in case without the grating obstacle. Meanwhile, due to the resistance effect, the integral momentum flux of the vertical jet was decayed with decrease of the aperture area ratio. It means that in case with the grating obstacle the integral jet penetration strength was decayed, although the local jet penetration to the stratification was stronger than that in case without the grating obstacle. Also, the slower stratification breakup could be observed with decrease of the aperture area ratio, indicating that stratification breakup rate to be discussed in detail considering every possible effect of a jet penetration.

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