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Horiguchi, Naoki; Yoshida, Hiroyuki; Kaneko, Akiko*; Abe, Yutaka*
Physics of Fluids, 37(3), p.033333_1 - 033333_20, 2025/03
Times Cited Count：0 Percentile：0.00(Mechanics)In a severe accident, as molten fuel is assumed to behave as a wall-impinging jet in a shallow coolant pool, atomize and accumulate as fuel debris, it is important to reveal the atomization mechanisms of the wall-impinging jet. This study aimed to reveal the atomization mechanisms in the vortex-like flow of a wall-impinging jet in a shallow pool of a liquid-liquid system, focusing on droplet formation as an elementary process of atomization. To quantitatively investigate these mechanisms, we applied quantification methods to three-dimensional interfacial data obtained by a previous experimental study using three-dimensional laser-induced fluorescence with index matching. Detailed observations of the spreading behavior of droplets and vortex-like flow, along with quantitative estimations, found out that the vortex-like flow is the dominant source of droplets on the atomization. Further investigations into the forces acting on the vortex-like flow found out the formation and collapse processes of the vortex-like flow. The accelerations of the normal forces acting on the vortex-like flow can be represented by superficial centrifugal acceleration and gravitational acceleration. Our next analysis focused on investigating droplet formation as the elementary process of atomization. The results showed two droplet formation patterns: liquid-film breaking patterns, wherein droplets directly form from the liquid film, and the surfing pattern, wherein droplets form from interfacial waves on the liquid film. Subsequently, the droplet data were grouped using dimensionless numbers and compared with theoretical lines describing the different droplet formation mechanisms. This comparison revealed the mechanisms of droplet formation within the vortex-like flow.
Horiguchi, Naoki; Yoshida, Hiroyuki; Kaneko, Akiko*; Abe, Yutaka*
Proceedings of 12th Japan-Korea Symposium on Nuclear Thermal Hydraulics and Safety (NTHAS12) (Internet), 6 Pages, 2022/10
For safety evaluation of nuclear reactors in severe accidents, it is important to estimate physical quantities of fragments generated from the molten fuel jet, which falls in a pool and breaks up. The evaluation method has been developed for the behavior as liquid jet with hydrodynamic interaction including fuel coolant interaction (FCI). In case of a shallow pool assumed in ex-vessel, the molten fuel jet is assumed to behave as wall-impinging liquid jet and to form liquid film flow spreading on the floor with/without fragmentation. In our research, focusing on hydrodynamic interaction and the transient 3-dimensional spreading on the floor, we have developed the evaluation method by numerical simulation using the two-phase flow simulation code with interface tracking method (TPFIT) developed by JAEA and, the experimental method using the 3D-LIF method in liquid-liquid system for the validation data. In our previous studies, we investigated the wall-impinging liquid jet behavior with fragmentation and observed that the liquid film flow had some characteristic parts transiently. Since it indicates that the quantities change depending on the parts and affect the safety evaluation, it is important to measure the quantities of the fragments generated from each part. This paper explains the measurement of the physical quantities of the fragments generated from each part of the wall-impinging liquid jet in a shallow pool for the validation of the numerical simulation. We conducted an experiment with the 3D-LIF method and segmented the experimental data based on the fragmentation point over the liquid film flow using the dispersed phase tracking method, developed by JAEA. Then, we measured the diameter and amount of the fragments from the segmented experimental data and investigated their changing trend.
Kimura, Fumihito*; Yamamura, Sota*; Fujiwara, Kota*; Yoshida, Hiroyuki; Saito, Shimpei*; Kaneko, Akiko*; Abe, Yutaka*
Nuclear Engineering and Design, 389, p.111660_1 - 111660_11, 2022/04
Times Cited Count：4 Percentile：40.92(Nuclear Science & Technology)Horiguchi, Naoki; Yoshida, Hiroyuki; Kaneko, Akiko*; Abe, Yutaka*
no journal, ,
JAEA has developed the evaluation method of a wall-impinging liquid jet in a shallow pool in a liquid-liquid system by numerical simulation. As a part of the development, to clarify the generation mechanism of the fragments, we identified the primary generation position of the fragments by post-processing the 3-dimensional interface shape data of the liquid jet using the 3D-LIF method and investigated the relationship between the generation position and the liquid film structure of the jet.
Masaki, Naoto*; Horiguchi, Naoki; Kaneko, Akiko*; Yoshida, Hiroyuki
no journal, ,
During a severe accident in a light water reactor, molten fuel can enter a water pool with atomization and accumulate as debris on the floor. Atomization is important to estimate debris sedimentation, and the interrelationship between interfacial shear stress and jet shape is a key aspect of the atomization process. To investigate this interrelationship, we have developed a simultaneous measurement method for interfacial shear stress and jet shape. However, this method was adapted to a cylindrical jet with a three-dimensional shape, and the positioning of a cross-section for PIV at the jet center was an additional issue. In this presentation, to solve these issues, we will show the result of obtaining interfacial shear stresses in cross-sections with a three-dimensional interfacial shape by simultaneous measurement using multi-sectional PIV and the 3D-LIF method.
Yamauchi, Yuki*; Masaki, Naoto*; Kaneko, Akiko*; Horiguchi, Naoki; Yoshida, Hiroyuki
no journal, ,
no abstracts in English
Masaki, Naoto*; Kaneko, Akiko*; Horiguchi, Naoki; Yoshida, Hiroyuki
no journal, ,
During severe accidents in light water reactors, molten fuel jets into the coolant pool and are atomized. The cooling of molten fuel occurs at the interface between the fuel and coolant and is enhanced by the increase of interface area with atomization. To achieve the stable cooling of molten fuel, it is important to understand the deformation of interface waves during atomization and the role of interfacial shear stress, which is indicated as a primary factor in previous studies. However, due to technical limitations imposed by heat and fluid properties, visualizing the interface shape and measuring shear stress in experiments using molten fuel is difficult. Therefore, this study enabled the calculation of interface shear stress by simultaneously obtaining the interface shape using the 3D-LIF method and the velocity field using using the multi-section PIV in simulated experiments. This presentation reports on the results of investigating the effect of shear stress on the deformation of interface waves based on the obtained data.
Horiguchi, Naoki; Yamamura, Sota*; Fujiwara, Kota*; Kaneko, Akiko*; Yoshida, Hiroyuki
no journal, ,
no abstracts in English
Yamauchi, Yuki*; Masaki, Naoto*; Kaneko, Akiko*; Horiguchi, Naoki; Yoshida, Hiroyuki
no journal, ,
no abstracts in English
Horiguchi, Naoki; Masaki, Naoto*; Kaneko, Akiko*; Yoshida, Hiroyuki
no journal, ,
With the development of numerical simulation for two-phase flow, the importance of the measurement of interface positions of two-phase flow and its uncertainty evaluation is increasing for the validation. The LIF (Laser Induced Fluorescence) method is used to capture the cross-section of a fluid with a fluorescent dye, and the 3D-LIF (3-Dimensional LIF) method is the LIF method given an additional scanning function for the normal direction of the cross-section. The 3D-LIF method is suitable for the measurement of three-dimensional measurement of interface positions, but the uncertainty evaluation of the measurement is difficult because that interfaces of two-phase flow are not static. The final goal of this study is to develop the uncertainty evaluation method of the measurement using the 3D-LIF method by making clear plastic structures simulating two-phase flow, which provide static interfaces. To this end, the objective of the study is to develop clear plastic structures. We report the results to make the structures by solidifying clear liquid resin with partial addition of a fluorescent dye and measure their interface positions using the 3D-LIF method.
Horiguchi, Naoki; Yamamura, Sota*; Yoshida, Hiroyuki; Abe, Yutaka*
no journal, ,
Specific measurement methods have been developed to understand multi-phase thermal-hydraulic behavior. By using these methods, we can obtain time series two and 3-dimensional spatial interface data of phases. These data are useful for providing validation data for advanced simulation methods based on multi-fluid computation fluid dynamics. For example, to understand FCI (fuel coolant interaction) behavior, specific measurements for fragments (dispersed phase) generated from the jet were measured, and interface and size of fragments were successfully evaluated. However, 3-dimensional data for velocity was not assessed, because there is no tracking method for individual dispersed phases like a tracking method of PTV (particle tracking velocimetry), which using time series 2-dimensional data. In this paper, we developed the dispersoid phase tracking method based on time series 3-dimensional interface data. To check the applicability of this method for 3-dimensional interface data, we used detailed two-phase simulation data by using TPFIT. In these data, there are 3-dimensional data of both interface and velocity distribution. Then, we can evaluate the correct dispersed phase velocity, and we can consider the accuracy of the developed method precisely. In this paper, we applied the developed method to simplified two-phase flow. The simplified flow means not to include coalescence and fragmentation of dispersoids. As a result, the tracking of one dispersoid performed successfully, but a standard deviation of the measuring error increased with the decrease of cell number of the dispersoid.
