Details of a Researcher - Kobayashi, Hiromichi

Papers - Kobayashi, Hiromichi

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スタンフォード大学の紹介

小林宏充

日本流体力学会誌ながれ (日本流体力学会) 26 ( 5 ) 345-348 2007.10

Research paper (other academic), Single Work

Backward-facing step calculations using the Shear Improved Smagorinsky Model

Federico Toschi, Hiromichi Kobayashi, Ugo Piomelli, Gianluca Iaccarino

Center for Turbulence Research Proceedings of the 2006 Summer Program (Center for Turbulence Research) 87-97 2006.12

Research paper (bulletin of university, research institution), Joint Work

Application of a local subgrid model based on coherent structures to complex geometries

Hiromichi Kobayashi

Center for Turbulence Research Annual Research Briefs 2006 (Center for Turbulence Research) 69-77 2006.12

Research paper (bulletin of university, research institution), Single Work

Can a spinning egg really jump?

Takahisa Mitsui, Kesao Aihara, Chikako Terayama, Hiromichi Kobayashi, and Yutaka Shimomura

Proceedings of the Royal Society A 462 ( 2074 ) 2897-2905 2006.10

Research paper (scientific journal), Joint Work, Accepted

Large eddy simulation of magnetohydrodynamic turbulent channel flows with local subgrid-scale model based on coherent structures

Hiromichi Kobayashi

Physics of Fluids (American Institute of Physics) 18 ( 4 ) 045107 2006.04

Research paper (scientific journal), Single Work, Accepted

A new methodology for Reynolds-averaged modeling based on the amalgamation of heuristic-modeling and turbulence-theory methods

Akira Yoshizawa, Shoiti Nisizima, Yutaka Shimomura, Hiromichi Kobayashi, Yuichi Matsuo, Hiroyuki Abe, and Hitoshi Fujiwara

Physics of Fluids (American Institute of Physics) 18 ( 3 ) 035109 2006.03

Research paper (scientific journal), Joint Work, Accepted

LES of MHD turbulent channel flows with a local SGS model based on coherent structures

Hiromichi Kobayashi

Center for Turbulence Research Annual Research Briefs 2005 (Center for Turbulence Research) 235-247 2005.12

Research paper (bulletin of university, research institution), Single Work

The subgrid-scale models based on coherent structures for rotating homogeneous turbulence and turbulent channel flow

Hiromichi Kobayashi

Physics of Fluids (American Institute of Physics) 17 ( 4 ) 045104 2005.04

Research paper (scientific journal), Single Work, Accepted

The subgrid-scale (SGS) models based on the coherent structure (CS) in grid-scale flow fields are proposed and are applied to (non-)rotating homogeneous turbulences and turbulent channel flows. The eddy viscosity is modeled by a coherent structure function (CSF) with a fixed model-parameter. The CSF is defined as the second invariant normalized by the magnitude of a velocity gradient tensor and plays a role of wall damping. The probability density function of the CSF is non-Gaussian showing an intermittency effect. The model parameter is locally determined, and it is always positive and has a small variance. These models satisfy a correct asymptotic behavior to a wall for incompressible flows. It is shown that the SGS models with an energy-decay suppression function which indicates also a pseudo-backscatter are consistent with the asymptotic material frame indifference in a rotating frame. Since the CSF characterizing turbulent flows has relation to the SGS energy dissipation, the present SGS models are applicable not only to (non-)rotating homogeneous and shear turbulences but also to laminar flows. The proposed models have almost the same performance as the dynamic Smagorinsky model for (non-)rotating homogeneous turbulences and turbulent channel flows, but these models do not need to average or clip the model parameter, use an explicit wall-damping function, or change the fixed-parameter, so that they are suitable for engineering applications of LES.

R-z Two-dimensional Numerical Simulations of a Frozen Inert Gas Plasma MHD Generator

Hiromichi Kobayashi, Seiji Nagai, Yoshihiro Okuno

IEEE Transactions on Plasma Science (The Institute of Electrical and Electronics Engineers) 33 ( 1 ) 197-204 2005.02

Research paper (scientific journal), Joint Work, Accepted

In a magnetohydrodynamics (MHD) power generation with a frozen inert gas plasma (FIP), the effect of the non-uniformity of the inlet plasma in the direction perpendicular to walls on the performance and the comparison of the performance with r-theta two-dimensional (2-D) numerical simulations are examined with r-z 2-D ones. The inlet non-uniformity of an ionization degree is kept throughout the channel and even in the boundary layer the state of the FIP is realized without an ionization instability. When the inlet ionization degree near the walls is higher than that in the main flow, the enthalpy extraction ratio decreases because the strong MHD interaction near the wall leads to the development of the boundary layer. On the other hand, it increases for the inverse distribution at the channel inlet, even if the introduced total inlet ionization degree is the same. In comparison with the results obtained
from the r-theta simulation, the development of the boundary layer results in the deterioration of the performance, and the optimal condition shifts to the low inlet ionization degree and the high load resistance.

Large Eddy Simulation for the Dynamic Clark Model with an Anisotropic Filter

Hiromichi Kobayashi

Hiyoshi Review of Natural Science, Keio University (慶応義塾大学出版会) ( 36 ) 15-25 2004.09

Research paper (bulletin of university, research institution), Single Work

大学一年生の物理への関心度と知識度調査

加藤万里子，小林宏充，鹿野川正彦

慶應義塾大学日吉紀要 (慶應義塾大学出版会) ( 35 ) 45-61 2004.03

Research paper (bulletin of university, research institution), Joint Work

Response to "Comment on 'Inapplicability of the dynamic Clark model to the large eddy simulation of incompressible tubulent channel flows'"

Hiromichi Kobayashi, Yutaka Shimomura

Physics of Fluids (American Institute of Physics) 16 ( 2 ) 492 2004.02

Research paper (scientific journal), Joint Work, Accepted

高温空気燃焼ボイラの熱特性に関する研究（第２報，数値計算による検討）

小林宏充，吉川邦夫

日本機械学会論文集Ｂ (日本機械学会) 69 ( 686 ) 2330-2336 2003.10

Research paper (scientific journal), Joint Work, Accepted

Thermal characteristics of a high temperature air combustion boiler is numerically examined. The high temperature air combustion is realized using a preheated air of about 800℃〜1000℃ under low oxygen content (〜5%). Numerical simulation reveals that more uniform temperature distribution in the boiler and higher heat transfer are obtainable using high temperature air in comparison with using normal temperature air owing to mild reactions in the high temperature field and heat recovery by regenerative burners. High speed injection of high temperature air into the boiler causes in-furnace exhaust gas recirculation, which results in low NOx emission. There is good agreement between experiment and numerical simulation in particular when using low calorific value gas, because more uniform temperature distribution is realized and average temperature in the boiler becomes lower.

Inapplicability of the dynamic Clark model to the large eddy simulation of incompressible turbulent channel flows

Hiromichi Kobayashi, Yutaka Shimomura

Physics of Fluids (American Institute of Physics) 15 ( 3 ) L29-L32 2003.03

Research paper (scientific journal), Joint Work, Accepted

Numerical Study on Performance of Disk MHD Generator Using Frozen Inert Gas Plasma

Hiromichi Kobayashi, Yukimasa Satou, Yoshihiro Okuno

IEEE Transactions on Plasma Science (The Institute of Electrical and Electronics Engineers) 30 ( 6 ) 2152-2159 2002.12

Research paper (scientific journal), Joint Work, Accepted

In an MHD generator using a frozen inert gas plasma (FIP), the availability of a frozen argon plasma, the influence of plasma uniformity at the generator inlet on the performance, and the feasibility of a large-scale generator are numerically examined by r-theta two-dimensional imulation. The FIP is produced by pre-ionizing inert gas without an alkali metal seed at the generator inlet, then the ionization degree of the plasma is kept almost constant in the whole of the channel because of considerable slow recombination of the inert gas just like frozen reaction plasma. It is found that not only helium but also argon frozen plasma MHD generation is realized, although highly accurate control of inlet onization degree is necessary for argon. It is important to reduce the nonuniformity of plasma properties at the generator inlet in order to raise the maximum enthalpy extraction ratio. Even for the large-scale generator with 1000MW thermal input, the ionization degree is kept almost constant in the whole of the channel and the high performance is obtainable. This result is extremely attractive for the FIP MHD generator.

Performance of High Temperature Air Combustion Boiler with Low NOx Emission

Hiromichi Kobayashi, Yohito Ito, Naoki Tsuruta, Kunio Yoshikawa

JSME International Journal, Series B (Japanese Society of Mechanical Engineering) 45 ( 3 ) 481-486 2002.08

Research paper (scientific journal), Joint Work, Accepted

Thermal performance in the experiments and three-dimensional numerical simulations for a high temperature air combustion boiler where fuel can be efficiently combusted by high temperature preheated air (800C-1000C) is examined. The boiler can burn not only natural gas but also low calorific gas (e.g. full gasification gas obtained from coal or wastes). In the boiler, four regenerative burners are installed. This boiler has new features that not only air but also gasification gas is heated up to 900C, and combination of burners is switched every 15 seconds where two burners are used as inlets of fuel and air and the other two burners are used as outlets of exhaust gas. Natural gas and syngas obtained from coal are burned. The NOx emission for each fuel is less than 50ppm. The heat transfer of three-dimensional calculation is predicted higher than that of experiment.

High Temperature Air Combustion Boiler for Low BTU Gas

K.Kawai, K.Yoshikawa, H.Kobayashi, J.S.Tsai, M.Matsuo and H.Katsushima

Energy Conversion and Management (Elsevier Science) 43 ( 9-12 ) 1563-1570 2002.06

Research paper (scientific journal), Joint Work, Accepted

A new concept boiler where fuel can be efficiently combusted by high temperature preheated air is proposed and experimental demonstration is done. This boiler is suitable for low BTU gas derived from gasification process of coal and wastes with no dioxin emission. This boiler is characterized by the following features; uniform heat flux field, augmentation of heat transfer, reduction of combustion noise level, suppression of NOx emission and compactness. Preliminary experiments using natural gas as a fuel demonstrate above distinct performance as well as good agreement with three-dimensional numerical simulation.

高温空気燃焼ボイラの熱特性に関する研究（第１報，実験による検討）

小林宏充，吉川邦夫

日本機械学会論文集Ｂ (日本機械学会) 67 ( 633 ) 2877-2882 2001.11

Research paper (scientific journal), Joint Work, Accepted

A new concept compact boiler using high temperature air is proposed and experimental demonstration is done. In the boiler, high temperature air combustion is realized. Fuel can be efficiently burned by high temperature preheated air of about 800C-1000C under low oxygen content ( < 5% ). The temperature distribution in the furnace is very uniform and there is no hot spot, so that low NOx emission ( < 40ppm) and relatively high average temperature in the furnace can be achieved. Thermal efficiency of more than 90% is accomplished including waste heat recovery of exhaust gas. This boiler is useful to partial load operation, because the response of thermal output is linear. This boiler is also suitable for low calorific value gas derived from gasification process of coal and wastes with no dioxin emission. Simulated low calorific value gas made from natural gas diluted with argon can be burned with low NOx emission.

凍結希ガスプラズマを利用したディスク形MHD発電機の性能数値計算

小林宏充，佐藤幸正，奥野喜裕

電気学会論文誌Ｂ (電気学会) 121 ( 8 ) 1023-1028 2001.08

Research paper (scientific journal), Joint Work, Accepted

MHD electrical power generation with frozen helium plasma (FHP) is examined numerically. The FHP can be initiated by pre-ionized helium without the alkali metal seed at the generator inlet. Since the three-body recombination coefficient of helium ions is low at the electron temperature above 5000K, the ionization degree can be kept almost constant in the entire region of the generator channel. The r-theta two-dimensional numerical results show that the performance of the FHP MHD generator is comparable to that of the seeded plasma MHD generator, if the additional power consumed to pre-ionization is ignored. In the FHP MHD generator, the ionization degree at the inlet should be controlled precisely, as well as the seed fraction in the seeded plasma MHD generator. Under the adequate inlet ionization degree for sustaining the FHP plasma, the plasma maintains the uniform structure. On the other hand, a slightly excess ionization degree causes the strong Lorentz force in the upstream region of the generator, then the generator performance is deteriorated.

The Performance of Dynamic Subgrid-Scale Models in the Large Eddy Simulation of Rotating Homogeneous Turbulence

Hiromichi Kobayashi, Yutaka Shimomura

Physics of Fluids (American Institute of Physics) 13 ( 8 ) 2350-2360 2001.08

Research paper (scientific journal), Joint Work, Accepted

The performance of dynamic subgrid-scale models is numerically examined in the large eddy simulation (LES) of rotating homogeneous turbulences in comparison with the corresponding filtered data of the direct numerical simulation (DNS). The examined dynamic SGS models are: the dynamic Smagorinsky model (DSM), the dynamic mixed model (DMM), the dynamic Clark model (DCM), and the dynamic two-parameter Clark model (DTCM). All models are mathematically reformulated in a rotating frame from the corresponding expressions in an inertial frame. It is shown that the DSM and the DMM are not consistent with the constraint of asymptotic material frame indifference, but the DCM and the DTCM are consistent. All models except the DSM show similar decays of the grid-scale turbulent energies both in non-rotating and in rotating frames; they agree well with the DNS in the non-rotating case, but they are slightly less dissipative than the DNS in the rotating case. The DSM underestimated the GS energy dissipation in the non-rotating case, though there is no major difference from other models in the rotating case. However, the DSM in a rotating frame, which takes a different form from that in an inertial frame, leads to an unphysical fluctuating decay for a homogeneous turbulence suddenly submitted to a rotation.

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