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Journal Articles

Influence of fluid viscosity on vortex cavitation at a suction pipe inlet

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kamide, Hideki; Kunugi, Tomoaki*

Nippon Genshiryoku Gakkai Wabun Rombunshi, 15(3), p.151 - 158, 2016/09

no abstracts in English

Journal Articles

Study on behavior of vortex cavitation around suction pipes in sodium-cooled fast reactor geometry

Ezure, Toshiki; Ito, Kei; Kamide, Hideki; Kunugi, Tomoaki*

Thermal Science and Engineering, 24(3), p.31 - 38, 2016/07

Journal Articles

Experimental measurement of vortex cavitation around a suction pipe inlet

Ezure, Toshiki; Ito, Kei; Kameyama, Yuri*; Kurihara, Akikazu; Kunugi, Tomoaki*

Konsoryu, 30(2), p.189 - 196, 2016/06

Journal Articles

Visualization of distribution of shear stress due to water vortex flow with SSLCC

Okazaki, Soichiro*; Ezure, Toshiki; Ohshima, Hiroyuki; Kawara, Zensaku*; Yokomine, Takehiko*; Kunugi, Tomoaki*

Proceedings of 10th Pacific Symposium on Flow Visualization and Image Processing (PSFVIP-10), 8 Pages, 2015/06

A visualization study is performed under suction vortex geometry in water. In the experiment, the shear-sensitive liquid crystal coating (SSLCC) is applied to grasp the distribution of wall shear stress under the suction votex flow. As the result, it was found that the peak value of wall shear stress is appeared at the center and edge of the projected area of suction pipe. The non-dimensional profile of wall shear stress obtained by suction vortex flow experiment agrees well with that of numerical simulation.

Journal Articles

A High-precision calculation method for interface normal and curvature on an unstructured grid

Ito, Kei; Kunugi, Tomoaki*; Ohno, Shuji; Kamide, Hideki; Ohshima, Hiroyuki

Journal of Computational Physics, 273, p.38 - 53, 2014/09

 Times Cited Count:11 Percentile:31.54(Computer Science, Interdisciplinary Applications)

Journal Articles

A Volume-conservative PLIC algorithm on three-dimensional fully unstructured meshes

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki; Kawamura, Takumi*

Computers & Fluids, 88, p.250 - 261, 2013/12

 Times Cited Count:15 Percentile:35.07(Computer Science, Interdisciplinary Applications)

The PLIC (Piecewise Linear Interface Calculation) algorithm is one of the volume-of-fluid algorithms. However, the PLIC algorithm needs complicated geometrical calculations for the reconstructions of the interfaces in interfacial cells, and therefore, the PLIC algorithm on unstructured meshes have not been studied enough. In this paper, the authors propose a new PLIC algorithm on unstructured meshes with arbitrary-shaped cells. In the proposed PLIC algorithm, several methods are developed or implemented. In addition, the volume fraction transport is improved by developing a volume-conservative algorithm in which gas and liquid volumes are conserved perfectly during the transport. As a result of the verification and validation tests, it is confirmed that the proposed PLIC algorithm enables the numerical simulations of interfacial dynamic behaviors with high accuracy even on unstructured meshes with highly-irregular cell arrangement.

Journal Articles

High-precision numerical scheme for vortical flow

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki

Applied Mathematics, 4(10A), p.17 - 25, 2013/10

In this study, a new high-precision numerical simulation scheme for vortical flows (vortex-based scheme) is proposed. This scheme identifies a vortical flow in each computational cell, and then, reconstructs a vortical velocity distribution based on the Burgers vortex model. In addition, a pressure distribution in the vicinity of the vortex center is also reconstructed. The momentum transfer is calculated with the reconstructed velocity and pressure distributions, and therefore, the vortex-based scheme can simulate vortical flows more accurately than the conventional schemes. In fact, as the simulation result of inviscid vortex attenuation problem, the vortex-based scheme shows lower simulation error compared to the conventional discretization schemes. Moreover, also in the numerical simulation of the quasi-steady vortical flow, the simulation accuracy of the vortex-based scheme is superior to those of the conventional schemes.

Journal Articles

Standard for prevention of gas entrainment phenomena in fast reactors, 1; Validations of CFD methods for reproducibilities of gas entrainment phenomena

Ohshima, Hiroyuki; Tanaka, Nobuatsu*; Eguchi, Yuzuru*; Nishimura, Motohiko*; Kunugi, Tomoaki*; Uchibori, Akihiro; Ito, Kei; Sakai, Takaaki

Nippon Genshiryoku Gakkai Wabun Rombunshi, 11(4), p.316 - 328, 2012/12

It is of importance for stable operations of sodium-cooled fast reactors (SFRs) to prevent gas entrainment (GE) phenomena due to free surface vortices. Therefore, the authors have been developing an evaluation method for GE based on computational fluid dynamics (CFD) methods. In this study, we determine the suitable CFD method for GE phenomena from several candidates through some numerical benchmarks. As the results, we obtain the following guideline for the vortex-induced gas entrainment. Free vortex flow around the vortex core can be correctly evaluated by using the appropriate numerical models such as enough mesh resolution, suitable advection solver, suitable turbulence and free surface modeling.

Journal Articles

Standard for prevention of gas entrainment phenomena in fast reactors, 2; Proposal of gas entrainment evaluation method

Ohshima, Hiroyuki; Eguchi, Yuzuru*; Kunugi, Tomoaki*; Kamide, Hideki; Sakai, Takaaki; Ito, Kei

Nippon Genshiryoku Gakkai Wabun Rombunshi, 11(4), p.329 - 339, 2012/12

For the stable operation of fast breeder reactors (FBRs), the occurrences of gas entrainment (GE) phenomena should be suppressed below an allowance level. Therefore, a reliable evaluation method for the GE phenomena is necessary to determine the operating conditions of FBRs. In this paper, the authors propose a GE evaluation method in which free surface vortices are identified from velocity fields by using the second invariant of velocity gradient tensor, and the GE evaluation parameters, e.g. gas core length, are calculated by using the Burgers vortex model. In addition, the standard for prevention of three kinds of the vortex-type GE are shown in consideration of experimental data, evaluation results with the proposed method and the comparison results of them. Finally, it is confirmed that the onset conditions of the vortex-type GE can be evaluated by the proposed method.

Journal Articles

High-precision calculation of interface normal on non-orthogonal mesh

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki

Konsoryu, 26(1), p.52 - 59, 2012/03

For the purpose of direct simulations of gas entrainment phenomenon in fast reactors, the authors are developing a high-precision simulation algorithm for gas-liquid two-phase flows on non-orthogonal meshes. In this paper, the calculation method for an interface normal is improved by developing a height function algorithm on non-orthogonal meshes. As a result of basic verification, the height function algorithm succeeds in reproducing rectilinear interfaces on a non-orthogonal triangular mesh. In addition, an interfacial curvature is calculated accurately based on the interface normal calculated by the height function algorithm.

Journal Articles

Numerical simulation of cavitation by sub-surface vortex; High-precision numerical simulation scheme for vertical flow

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki

Nippon Kikai Gakkai Rombunshu, B, 78(786), p.254 - 262, 2012/02

The cavitation due to sub-surface vortex, which can damage structural surfaces of a large-scale sodium-cooled fast reactor in Japan, have been studied. The authors are developing a CFD code to simulate the cavitation accurately. In this paper, as the first part of the development, a high-precision simulation scheme for vortical flows is presented. In this scheme, a vortical flow is identified in each cell and a vortical velocity distribution is determined locally to be consistent with the local velocity distribution. Then, the calculations of momentum transport through cell faces are performed in consideration with the vortical velocity distribution. As a fundamental verification of the developed scheme, inviscid vortex attenuation in two-dimensional domain is simulated. As a result, it is confirmed that the developed scheme can simulate vortical flows more accurately than conventional schemes.

Journal Articles

A High-precision unstructured adaptive mesh technique for gas-liquid two-phase flows

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki

International Journal for Numerical Methods in Fluids, 67(11), p.1571 - 1589, 2011/12

 Times Cited Count:8 Percentile:49.45(Computer Science, Interdisciplinary Applications)

In this paper, a high-precision unstructured adaptive mesh technique for gas-liquid two-phase flows is developed and verified/validated. In the unstructured adaptive mesh technique, the PLIC algorithm is employed to simulate interfacial dynamic behaviors and, therefore, the reconstruction method for the interfaces in refined cells is developed, which satisfies the gas and liquid volume conservations and geometrical conservations of interfaces. In addition, the physics-based consideration is performed on the momentum calculations near interfaces, and the calculation method with gas and liquid momentum conservations is developed. For verification, the slotted-disk revolution problem is solved and the unstructured adaptive mesh technique succeeds in reproducing the slotted-disk shape accurately. The dam-break problem is also simulated and the momentum conservative calculation method succeeds in providing physically appropriate results, which show good agreements with experimental data.

Journal Articles

Two-phase flow simulation of gas entrainment phenomena in large-scale experimental model of sodium-cooled fast reactor

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki; Kawamura, Takumi*

Progress in Nuclear Science and Technology (Internet), 2, p.114 - 119, 2011/10

The authors have been developed a high-precision and high-performance numerical simulation algorithm for gas-liquid two-phase flows to simulate the gas entrainment (GE) phenomena in fast reactors. In this paper, the developed simulation algorithm is applied to the GE phenomena in a large-scale water experiment. As a result of the unsteady simulation, a typical interfacial dynamic behavior, i.e. the development of a gas core (interfacial dent), is well simulated. Therefore, it is confirmed that the developed simulation algorithm is suitable to evaluate numerically the GE phenomena in the fast reactors.

Journal Articles

Development of laser welding simulation code with advanced numerical models

Yamashita, Susumu; Yonemoto, Yukihiro; Yamada, Tomonori; Kunugi, Tomoaki*; Muramatsu, Toshiharu

Yosetsu Gakkai Rombunshu (Internet), 29(3), p.48s - 52s, 2011/08

Quantitative evaluation and controlling the residual stress which is induced by laser welding is of important problem for a life extension of FBRs (Fast Breeder Reactors) and the guarantee of the reliability of the repair processes. Numerical simulation is an effective tool for deep understanding of their problems and it needs to have high accuracy, robustness and reliability. We have recently constructed the fully parallelized laser welding simulation code which satisfies above aspects using some advanced numerical models. Concretely, VSIAM3 numerical model as the spatial discretization, an efficient free surface capturing scheme, THINC scheme, and FAVOR method as the solid phase expression has been applied to the code. We have conducted laser welding simulations and obtained some reasonable results. Therefore, the numerical model will be contributed to the repairing technology of a laser welding.

Journal Articles

High-precision reconstruction of gas-liquid interface in PLIC-VOF framework on unstructured mesh

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki

Computational Fluid Dynamics 2010, p.563 - 567, 2011/05

 Times Cited Count:0 Percentile:100

The authors are developing a high-precision numerical simulation algorithm for gas-liquid two-phase flows to simulate gas entrainment phenomena in fast reactors. In this study, the calculation method for the unit vector normal to a gas-liquid interface in the high-precision volume-of-fluid algorithm (PLIC-VOF) is improved on two-dimensional unstructured meshes. As the result of a basic verification, the improved calculation method succeeds in reproducing rectilinear interfaces on an unstructured triangular mesh. In addition, it is confirmed that the improved calculation method enhances the simulation accuracy of the well-known slotted-disk revolution problem on an unstructured mesh.

Journal Articles

Real-scale numerical simulation of gas entrainment phenomena in fast reactor

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki; Kawamura, Takumi*

Nippon Kikai Gakkai Rombunshu, B, 77(776), p.978 - 981, 2011/04

To evaluate gas entrainment (GE) phenomena in a large-scale sodium-cooled fast reactor, the authors are developing a high-precision numerical simulation algorithm for gas-liquid two-phase flows based on a volume-of-fluid methodology. It is confirmed that the developed simulation algorithm can reproduce the GE phenomena in a simple experiment. In this study, the simulation algorithm is applied to a real-scale GE test to check the applicability of the algorithm to the GE phenomena in the fast reactor. As a result, transient behaviors of the vortical flows around the pipes and the accompanied GE phenomena are simulated well. In particular, the origin of the flow which induces the GE phenomena is showed clearly. Finally, from the investigation of a lot of GE phenomena observed in the simulation result, it is verified that the GE phenomena by relatively strong vortical flows are important in terms of the GE suppression in the fast reactor.

Journal Articles

Consideration of optimum algorithm for acceleration of a multi-phase flow analysis with GPU

Nagatake, Taku; Kunugi, Tomoaki*; Takase, Kazuyuki

Dai-24-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Rombunshu (USB Flash Drive), 4 Pages, 2010/12

GPU (Graphics Processing Unit) has been developed for drawing system in computer. In order to achieve the high-performance computing for rendering high-quality 3D graphics, the GPU has many processing units and the wide memory bandwidth. Nowadays, the performance of GPU becomes much higher than that of CPU (Central Processing Unit), so that the attempt to make use of GPU for the science calculation and general purpose is performed: This attempt is called "GPGPU" (General Purpose GPU) or "GPU computing". Now we are developing MARS (Multi-interfaces Advection and Reconstruction Solver) (1) with GPU. The MARS is one of the surface volume tracking methods for multi-phase flows. In this paper, the performance of GPU is compared to the CPU. And the parallelized method for the multi-GPU system is considered.

Journal Articles

A High-precision numerical simulation scheme for vortical flows

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki

Dai-24-Kai Suchi Ryutai Rikigaku Shimpojiumu Koen Rombunshu (USB Flash Drive), 5 Pages, 2010/12

In the design study of a large-scale sodium-cooled fast reactor in Japan (JSFR), an innovative concept with a compact reactor vessel and resulting higher coolant velocity in the vessel has been examined. Such a concept may causes several thermal-hydraulics issues in the reactor vessel. One of very important issues is the cavitation phenomena due to a sub-surface vortex caused near the suction mouth of an outlet pipe. For the structural integrity, the cavitation phenomena have to be suppressed. However, the onset condition of the cavitation phenomena can not be clarified easily because the cavitation phenomena shows highly complicated behaviors associated with phase change. Therefore, the authors are developing a high-precision numerical simulation scheme for vortical flows to simulate the cavitation phenomena accurately and efficiently. In this paper, a high-precision numerical simulation scheme for vortical flows is developed and a basic verification of the scheme is conducted.

Journal Articles

Application of GPU to Multi-interfaces Advection and Reconstruction Solver (MARS)

Nagatake, Taku; Kunugi, Tomoaki*; Takase, Kazuyuki

Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 5 Pages, 2010/10

In the nuclear engineering fields, a high performance computer system is necessary to perform the large scale computations. Recently, a GPU (Graphics Processing Unit) has been developed as a rendering computational system in order to reduce a CPU (Central Processing Unit) load. The GPU consists of many processing units and a wide memory bandwidth in order to achieve the high-performance computing for rendering the high quality 3D objects. Nowadays, the performance of GPU has become much higher than that of the CPU, so the attempt to make use of the GPU for the scientific computations and more broad purposes is being performed. In this study, the MARS (Multi-interfaces Advection and Reconstruction Solver) which is one of the interface volume tracking methods for multiphase flows was developed by using the GPU.

Journal Articles

Two-phase flow simulation of gas entrainment phenomena in large-scale fast reactor

Ito, Kei; Kunugi, Tomoaki*; Ohshima, Hiroyuki; Kawamura, Takumi*

Proceedings of Joint International Conference of 7th Supercomputing in Nuclear Application and 3rd Monte Carlo (SNA + MC 2010) (USB Flash Drive), 6 Pages, 2010/10

The authors have been developed a high-precision numerical simulation algorithm for gas-liquid two-phase flows to simulate the gas entrainment (GE) phenomena in a large-sized sodium-cooled fast reactor in Japan (JSFR). In this paper, the developed simulation algorithm is applied to the GE phenomena in a large-scale water experiment which models the complicated geometrical configurations of the system components in JSFR. For the numerical simulation, an unstructured mesh with about one million cells are generated and optimized to simulate the interfacial deformations near inlet and outlet pipes which cause vortical flows behind them to induce the GE phenomena. As a result of the unsteady simulation, a typical interfacial dynamic behavior, i.e. the development of a gas core (interfacial dent), is well simulated. Therefore, it is confirmed that the developed simulation algorithm is suitable to evaluate numerically the GE phenomena in JSFR.

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