記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Kyohei Yada;Tetsushi Simomura;Shenghong Ju;Makoto Kashiwagi;Hideyuki Okada;Tadaaki Nagao;Koji Tsuda;Junichiro Shiomi
We computationally designed an ultranarrow-band wavelength-selective thermal radiator via a materials informatics method alternating between Bayesian optimization and thermal electromagnetic field calculation. For a given target infrared wavelength, the optimal structure was efficiently identified from over 8 billion candidates of multilayers consisting of multiple components (Si, Ge, and SiO2). The resulting optimized structure is an aperiodic multilayered metamaterial exhibiting high and sharp emissivity with a Q-factor of 273. The designed metamaterials were then fabricated, and reasonable experimental realization of the optimal performance was achieved with a Q-factor of 188, which is significantly higher than those of structures empirically designed and fabricated in the past. This is the first demonstration of the experimental realization of metamaterials designed by Bayesian optimization. The results facilitate the machine-learning-based design of metamaterials and advance our understanding of the narrow-band thermal emission mechanism of aperiodic multilayered metamaterials.

DOI： 10.1021/acscentsci.8b00802

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A. Sakurai;Y. Matsuno
In this study, a tungsten-SiO2-based metal–insulator–metal-structured metasurface for the thermal emitter of the thermophotovoltaic system was designed and fabricated. The proposed emitter was fabricated by applying the photolithography method. The fabricated emitter has high emissivity in the visible to near-infrared region and shows excellent wavelength selectivity. This spectral emissivity tendency agreed well with the result calculated by the finite-difference time-domain method. Additionally, the underlying mechanism of its emission was scrutinized. Study of the fabrication process and theoretical mechanisms of the emission, clarified in this research, will be fundamental to design the wavelength-selective thermal emitter.

DOI： 10.3390/mi10020157

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Takuma Kogawa;Lin Chen;Junnosuke Okajima;Atsushi Sakurai;Atsuki Komiya;Shigenao Maruyama
To use and understand the large-scale natural convection in the building and systems, heat transfer analysis of the natural convection with radiation is important. The radiation effect is influenced by concentration of the participating media in the considered system. In this study, an effects of concentration of participating media on turbulent natural convection inside a cubic cavity were investigated. The turbulence effect was modeled by large eddy simulation. Further, the radiative heat transfer was calculated by the radiation element method using the ray emission model. In addition, the gas radiation was modeled by the full-spectrum k-distribution method. By varying the partial pressures of H2O and CO2, the effect of the participating media were evaluated. From the calculation, gas radiation effects affected the flow instability and restrained the temperature stratification when the concentration of the participating media was higher. However, the convective heat transfer have not been affected by the significant flow instability by the radiation effects.

DOI： 10.1016/j.applthermaleng.2017.11.135

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Ryo Kanbayashi;Koji Matsubara
We performed a direct numerical simulation (DNS) of the turbulent natural convection between two parallel plates at a Rayleigh number of Ra = 8.0 × 106, focusing on the turbulent natural convection affected by radiation in an optically thick fluid (τ ≥ 10). When the effects of the radiation were considered, the flow structure and temperature distribution in the channel changed as the optical thickness of the fluid increased. The effects of the radiation on the turbulent natural convection were clearly explained by the turbulence statistics from the DNS results.

DOI： 10.1080/10407782.2017.1412713

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Yuki Matsuno;Atsushi Sakurai
Metasurfaces with metal-insulator-metal structures have attracted significant attention because of their high optical performance. Their spectral emissivity/absorptivity can be modulated with geometrically controlled electromagnetic resonances. However, practical fabrication of these materials in the meter scale remains a challenge. In the present study, an aluminum-and ceria-based metasurface that exhibits nearly perfect emission/absorption in the infrared region was designed. Furthermore, we succeeded in fabricating the proposed metasurface in the meter scale via photolithography and wet etching. This study enhances understanding of underlying resonance mechanisms with electromagnetic simulations and equivalent circuit model, and will facilitate the experimental design of high-efficiency largearea metasurfaces. (C) 2017 Optical Society of America

DOI： 10.1364/OME.7.000618

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Yuki Matsuno;Atsushi Sakurai
The purpose of this study is to clarify the optical characteristics of a Tungsten SiO2-based film-couple metamaterial with a fishnet-shaped grating, and we aim to show that this structure could potentially be used a solar selective absorber for a solar thermophotovoltaic system. The proposed film-coupled metamateris absorber combined with a fishnet-shaped grating shows significant enhancement in its absorption in the spectral region compared with a flat Tungsten surface, and it keeps its spectral emission low in the infrare region, thereby reducing radiative heat loss. The underlying mechanisms of the proposed absorber are discusse through a 3D full-wave electromagnetic simulation, the results of which are compared with that of theoretic equations. Furthermore, its spectral absorption under oblique incident light at the transverse magnetic am transverse electric waves is scrutinized. The underlying absorption mechanisms and relations between eac optical resonance are discussed in this paper and will prove to be fundamental not only in the design of selective absorbers but also in other wavelength-selective thermal radiation controlling devices.

DOI： 10.1016/j.optcom.2016.10.044

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Takuma Kogawa;Junnosuke Okajima;Astushi Sakurai;Atsuki Komiya;Shigenao Maruyama
The turbulence structure, boundary layer, and heat transfer of turbulent natural convection, including radiation effects inside the cubic cavity, were investigated in this study. Large eddy simulation was conducted, and Vreman model was adopted for the dynamic subgrid-scale model. To calculate the radiative heat flux efficiently, a coupled calculation method, using the radiation element method by ray emission model, was constructed. To separate the radiation effects of the gas and surface radiations, four calculation conditions have been analyzed; non-radiation, gas radiation, surface radiation, and combined radiation. Observing the vortices structure using the Q value revealed that the surface radiation effect was more dominant for the flow instability than the gas radiation effect. An evaluation of the boundary layers for both the gas and surface radiation effects showed that the flow circulation inside the cubic cavity was enhanced. The surface radiation was dominant in the generation of the shear stress by the turbulent flow. The total heat transfer, which includes the convective and radiative heat transfers, have been investigated. The surface radiation affected on the radiative heat transfer significantly as compared to the gas radiation. The radiation effects changed the radiative heat transfers, while the convective heat transfers of all the calculation conditions were similar. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2016.08.059

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Tomoaki Kawamata
We numerically investigate a solar-selective absorber with tungsten core-shell nano particle arrays embedded in an SiO2 layer. The 3D full-wave finite-difference time-domain (FDTD) simulations are performed to investigate the geometric effects of different types of solar-selective absorbers. Consequently, broadband light absorption was achieved with either a tungsten nanoparticle array or a tungsten core-shell nanoparticle array because of the strong electric field enhancement in the gap between the core nanoparticles. The solar performance of the proposed structure is shown for high-efficiency solar light absorption. This study enhances understanding of the light absorption mechanism of metallic nanoparticle/dielectric composite and facilitates the design of high-efficiency solar-selective absorbers. (C) 2016 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jqsrt.2016.08.005

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Bo Zhao;Atsushi Sakurai;Zhuomin M. Zhang
Due to the interference effect, the reflectance and transmittance of an arbitrary linearly polarized wave cannot be fully described by the reflectance and transmittance of transverse electric and transverse magnetic waves. In this work, the polarization dependence of reflectance and transmittance for anisotropic metamaterials is examined. The explicit mathematical relationship between the Fresnel coefficients and the reflectance (or transmittance) for a given polarization angle is derived. A method is presented that can be used to obtain the reflectance (or transmittance) for any polarization angle from three other polarizations. Several different anisotropic metamaterials are numerically investigated with the finite-difference time-domain technique to elucidate the polarization dependence of reflectance or transmittance. The reflectance and transmittance obtained from the three-polarization-angle method are in agreement with those from the rigorous numerical simulation.

DOI： 10.2514/1.T4587

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Bo Zhao;Zhuomin M. Zhang
This work deals with the spectral radiative properties of metamaterials made of a 2D metallic pattern on a dielectric thin film that separates the top periodic structure from a metal ground plane. Two distinct patterns are considered: one consists of disconnected double-rectangle gold pattern and the other is made of L-shape pattern. Both structures exhibit dual-band emission or absorption peaks in the infrared region. Unlike the disconnected rectangular pattern for which the normal emittance is independent of the polarization angle, the L-shape structure shows strong polarization dependent due to near-field coupling. The electromagnetic fields at the resonant frequencies are analyzed using the finite-difference time-domain technique to elucidate the physical mechanisms accounting for the different behaviors. For both structures, the resonance mechanisms can be explained by magnetic polaritons. Inductor-capacitor circuit models are developed to quantitatively predict the resonance frequencies. This work helps the understanding of polarization dependence in metamaterials and may facilitate their applications in biosensing and infrared spectroscopic system. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jqsrt.2014.11.018

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

K. Matsubara;H. Sakai;Y. Kazuma;A. Sakurai;T. Kodama;N. Gokon;H.S. Cho;K. Yoshida
This study describes the flow and thermal field of a two-tower fluidized receiver, aimed to be incorporated into a beam-down reflector system. An experimental visualization and numerical simulation were made to accumulate phenomenological knowledge, in order to complete the design of a demonstration model. Visualization of the cold particle bed with no irradiation revealed that global circulation occurs between the two towers by the aeration with different line velocities. The numerical simulation revealed that this global circulation enhances the transport of sensible heat from the irradiated layer in the high pressure tower to the low pressure tower. The global circulation in the two-tower fluidized receiver has the potential to be extended for use in a thermal receiver and direct storage system. Unexpectedly, local circulations occur on the high and low pressure sides, and are stronger than the global circulation. These local circulations contribute to the thermal mixing in each tower. The bottom distributor on the low pressure side can cause an uprising flow which leads to the local circulation. The design of the distributor is suggested to be elaborated based on these findings. (C) 2015 The Authors. Published by Elsevier Ltd.

DOI： 10.1016/j.egypro.2015.03.057

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Koji Matsubara;Yuki Kazuma;Atsushi Sakurai;Tatsuya Kodama;Nobuyuki Gokon;Hyun-Seok Cho;Kazuo Yoshida;Yoshinori Nagase
This study proposes a t wo-tower t ype fluidized receiver for receiving concentrated s olar light at high temperatures is proposed. This fluidized receiver is coupled with the Miyazaki beam-down reflector system. The visualization and the numerical simulation was made for the laboratory model to show the fluid-dynamics and the heat transport as well as to elaborate the existing demonstration model. The experimental visualization of the cold model demonstrated that in each tower, the particles are moved by the aerated organized flow. The numerical simulation was made using the thermal input cited from the 5.0kWth sun simulator. The numerical simulation demonstrated that the inner particles are heated above 950 °C after 3.0 minutes of the aeration start time. The increase in temperature is caused by the intrusion of the heated particles from the high-pressure side tower to the low-pressure side tower. It is thus suggested that collective circulation occurs between high- and low-pressure side towers and this can be utilized for a direct thermal storage system.

DOI： 10.3775/jie.94.1323

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Bo Zhao;Zhuomin M. Zhang
Metamaterial thermal emitters and absorbers have been widely studied for different geometric patterns by exciting a variety of electromagnetic resonances. A resistor-inductor-capacitor (RLC) circuit model is developed to describe the magnetic resonances (i.e. magnetic polaritons) inside the structures. The RLC circuit model allows the prediction of not only the resonance frequency, but also the full width at half maximum and quality factor for various geometric patterns. The parameters predicted by the RLC model are compared with the finite-difference time-domain simulation. The magnetic field distribution and the power dissipation density profile are also used to justify the RLC circuit model. The geometric effects on the resonance characteristics are elucidated in the wire (or strip), cross, and square patterned metamaterial in the infrared region. This study will facilitate the design of metamaterial absorbers and emitters based on magnetic polaritons. (C) 2014 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jqsrt.2014.07.024

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Hiroya Tanikawa;Makoto Yamada
The purpose of this study is to computationally design a wide-angle cermet-based solar selective absorber for high temperature applications by using a characteristic matrix method and a genetic algorithm. The present study investigates a solar selective absorber with tungsten-silica (W-SiO2) cermet. Multilayer structures of 1, 2, 3, and 4 layers and a wide range of metal volume fractions are optimized. The predicted radiative properties show good solar performance, i.e., thermal emittances, especially beyond 2 mu m, are quite low, in contrast, solar absorptance levels are successfully high with wide angular range, so that solar photons are effectively absorbed and infrared radiative heat loss can be decreased. (C) 2013 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jqsrt.2013.03.004

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記述言語：英語   掲載種別：研究論文（研究会，シンポジウム資料等）  

Zhuomin Zhang;Shigenao Maruyama;Atsushi Sakurai;M. Pinar Menguc

DOI： 10.1016/j.jqsrt.2013.06.012

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

K. Matsubara;Y. Kazuma;A. Sakurai;S. Suzuki;L. Soon-Jae;T. Kodama;N. Gokon;C. Hyun Seok;K. Yoshida
This study proposes a novel fluidized receiver for absorbing concentrated solar light at high temperatures. Previously, a tubular receiver and a volumetric receiver were developed to make high-temperature air for a solar gas turbine system. The aim was to combine these elements with a tower reflector; however, it was challenging to install these heavy receivers on the top of the tower. Currently, a fluidized receiver prototype is tested by a 3 kWh solar simulator in preparation for a field test at the Miyazaki beam-down reflector system. The fluid dynamics of the prototype receiver is numerically investigated. The currently treated receiver is an inner-circulating fluidized bed spouted by concentric gas streams with high and low velocities in the center and outer annulus, respectively. The draft tube is submerged in the particles to organize particle circulation. Concentrated light irradiates the particles through a quartz window at the top of the receiver container. Such a fluidized bed was first adopted by Kodama et al. for thermochemical reactions; however, it is currently pursued for its potential as a high-temperature receiver aimed at concentrated solar power generation. Experiments of the prototype receiver (inner diameter = 45 mm) demonstrated that the inner particles are heated to a temperature greater than 900 degrees C and that an increase of the central gas velocity removes the excess temperature near the particle bed surface. A numerical computation suggests that the large-scale circulation of particles leads to the activation of thermal mixing. The currently proposed receiver is thus expected to attenuate re-radiation losses likely to occur in a conventional volumetric porous receiver. The scale-up of the receiver is being considered by the numerical computation for a field test in the Miyazaki 100 kWh beam-down reflector system. (C) 2013 The Authors. Published by Elsevier Ltd. This is an open access article under the CC BY-NC-ND license

DOI： 10.1016/j.egypro.2014.03.048

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掲載種別：研究論文（国際会議プロシーディングス）  

Atsushi Sakurai;Bo Zhao;Zhuomin M. Zhang

DOI： 10.1615/ihtc15.rad.009012

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Koji Matsubara;Kenji Takakuwa;Ryo Kanbayashi
The purpose of this study is to clarify the radiation effects on mixed turbulent convection in a horizontal channel. The present study provides turbulence statistics using direct numerical simulation (DNS) in an optically thin medium. When the radiation effect is considered, the flow structure and the temperature distribution in the channel change with an increase in the optical thickness of the fluid. The radiation effect changes the distributions of the temperature fluctuation intensity and the turbulent heat flux. These radiation effects on mixed convection can be clearly explained by the turbulence statistics obtained from the DNS results. (C) 2012 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.ijheatmasstransfer.2012.01.006

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Koji Matsubara;Atsushi Sakurai;Takahiro Miura;Takuya Kawabata
The near-wall turbulent heat transport of the three orthogonal directions was directly solved for the Prandtl numbers ranging from 0.025 to 5.0 to validate the algebraic models of the turbulent heat flux. Two kinds of thermal situations were considered in the low Reynolds number turbulent flow: (a) the case with a uniform heat flux in the spanwise direction (UHF) and (b) the case with the mean spanwise temperature gradient (STG). Among the turbulent heat flux models tested, the model of Rogers preferably predicted over the treated range of the Prandtl numbers, but it failed to reproduce the low Prandtl number effects very accurately. This paper revealed that the coefficient of the Rotta model can be modified to include the low Prandtl number effects by means of the correlation between the exact coefficient suggested by DNS and the Prandtl number. [DOI: 10.1115/1.4005077]

DOI： 10.1115/1.4005077

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Koji Matsubara;Katsuya Nishiwaki;Okiteru Fukuda;Togo Yamaguchi;Atsushi Sakurai
A newly developed electric furnace was used to pyrolyze benzene, methane, or acetylene diluted by a nonreactive gas, and the carbon aggregates were separated from the hydrogen-rich gases. The temperature was changed up to 2200K for various levels of initial concentration of hydrocarbon and residence time, and how the experimental parameters affected the mean diameter of carbon aggregates was examined. The temperature increase in experiments led to reduction of the mean diameter of the carbon aggregates, whereas increase in the initial concentration of hydrocarbon or the residence time resulted in slightly lifting it. The mean diameter removed of temperature effects correlated well with the initial carbon atom mol concentration of hydrocarbon, N-C, and this parameter was used to develop the experimental equations. This article presents three kinds of experimental equations, and the prediction accuracy was confirmed to be improved when accounting for increasing the experimental parameters.

DOI： 10.1080/00102202.2012.691582

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

Takahiro Miura;Koji Matsubara;Atsushi Sakurai
Direct numerical simulation was performed for air turbulent flows and heat transfer in a channel with square ribs attached to one wall. The spatially advancing cases and the fully advanced cases were both treated for the bulk Reynolds number of about 4,560. The rib height, H, was kept constant at 0.2 times the channel half-width, whereas the rib pitch was changed from Pi = 2H to 16 H. The heat transfer performance was evaluated using the ratio between the mean Nusselt number of the ribbed case and that of the smooth case requiring the same pumping power. This ratio was maximized at Pi/H = 9 for the fully advanced cases, but at Pi/H = 2 or 4 for the advancing cases. The mechanisms leading to this difference were discussed through turbulence statistics and their visualization. The thin thermal boundary layer in the advancing region was shown to increase heat transfer on the extended surface of Pi/H = 2 and 4, resulting the higher heat transfer performance than the case of sparse ribs. © 2012 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.78.607

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Takahiro Miura;Koji Matsubara;Atsushi Sakurai
Heat transfer and fluid flow in a single-rib mounting channel were investigated by directly solving Navier-Stokes and energy equations. The flow and thermal fields were considered to be fully developed at the inlet of the channel, and the simulation was made for spatial advancement of turbulent heat transfer. The Reynolds number based on the friction velocity at the inlet and the channel half width was 150. The Prandtl number was 0.71. The budgets for turbulent heat fluxes and temperature variance at various sections were presented and were investigated, which would be useful for testing and developing turbulence models. Near a circular vortex in front of the rib, pressure diffusion terms made an important contribution. Remarkable production terms were generated near a reattachment point. Production and dissipation terms were not dominant in front of and above the rib, and a time scale ratio exceeded 2.0 in the region.

DOI： 10.1299/jtst.7.120

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記述言語：日本語   出版者・発行元：一般社団法人日本エネルギー学会  

Double-walled reactor tubes with molten-salt thermal storage were developed for solar air receiver to generate electricity and for solar reforming to produce solar fuel. A mixture of Na_2CO_3 and MgO was loaded as a thermal storage medium into the outer annulus of that. Performances of the reactor tubes were studied as an air receiver and as a reformer tube in the present study.

DOI： 10.20550/jietaikaiyoushi.21.0_232

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Koji Matsubara;Atsushi Sakurai;Kenya Yamazaki;Makoto Takeda
Direct numerical simulation was performed for the spatially advancing turbulent flow in a two-dimensional curved channel. The fully developed turbulence was introduced into the curved channel through a straight part, and observation was made for how the near-wall turbulence advanced along curved walls. The frictional Reynolds number, Re(tau 0), was fixed at 150, whereas the radius ratio of the curved channel, alpha, was changed at three steps; 0.8, 0.92, and 0.975. Five computational tests were performed, which include simulations with changing the spanwise length of the channel or the grid arrangement. The maximum number of grid points was 43,610,112 (=936 x 91 x 512) used in the case of alpha = 0.92. Numerical results for the curved flow were nearly free from the grid arrangement or the spanwise length of the channel, and changes of the mean velocity qualitatively agreed with the experiment by Kobayashi [Trans. Jpn. Soc. Mech. Eng., Ser. B 57, 4064 (1991)], which both supported credibility of the simulation. The spanwise pre-multiplied power spectrum and the spanwise two-point correlation captured the peaks corresponding to the micro-scale structures near the straight wall, which continuously grew along the concave wall and advanced to exhibit the wave length of organized flows. Therefore, the micro-scale structures such as quasi-stream vortices and the ejection near the outer wall of the straight channel were suggested to trigger the onset of initial seeds of the organized structure, which grew into the large scale vortices expanding almost over the channel width.(C) 2011 American Institute of Physics. [doi: 10.1063/1.3584126]

DOI： 10.1063/1.3584126

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Koji Matsubara;Takahiro Miura;Atsushi Sakurai;Kenya Yamazaki;Makoto Takeda
Direct numerical simulation was performed for the spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel equating the radius ratio to 0.92 or 0.8. The frictional Reynolds number was fixed at 150, whereas the Prandtl number was set at 0.71. According to the numerical result, the remarkable enhancement of heat transfer occurred on the outer wall, suggesting the organized vortex activated the heat transfer. The budgets of Reynolds stresses clarified that the onset and growth of the organized flow was assisted by the direct energy transfer from the mean flow.

DOI： 10.1080/10407782.2011.588562

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

内田高志;松原幸治;三浦貴広;太刀川卓;櫻井篤
Direct numerical simulation was performed for a spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel. A rib was placed on either an inner-or outer-wall of the straight part nearby curved-channel inlet for controlling the flow and thermal fields. Outer-wall was heated at the constant temperature and inner-wall was cooled similarly. In the simulation, fully developed flow and temperature computed by the straight channel was given to the inlet of curved channel domain. The frictional Reynolds number was assigned at 150, and the Prandtl number was given 0.71. When a rib was attached to the inner-wall, heat transfer in the upstream region of curved channel was enhanced effectively. On the other hand, placing a rib on the outer-wall caused an enhancement of heat transfer in the relatively downstream region of curved part, suggesting active heat transport of the large-scale vortices. Consequently, the inner-rib case affected more greatly on heat transfer than the outer-rib case. Mean velocity vector and power spectrum analysis implied that development of coherent structures near the outer-wall were controlled by a rib. It was found that inner-rib restrained large-scale vortex, while outer-rib promoted growth and power of large-scale vortex. © 2011 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.77.2170

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Ryo Kanbayashi;Koji Matsubara;Shigenao Maruyama
Thermal radiation in a turbulent natural convection plays an important role in a wide area of engineering and nature. The purposes of this study are to investigate the effects of turbulent fluctuation on radiative heat transfer, and to evaluate radiative heat transfer models applied to turbulent natural convection. The present radiative heat transfer analysis of a turbulent natural convection using direct numerical simulation (DNS) provides a useful fundamental data for the complete coupling simulation in the future.

DOI： 10.1299/jtst.6.449

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記述言語：英語   掲載種別：研究論文（国際会議プロシーディングス）  

Takashi Uchida;Koji Matsubara;Takahiro Miura;Atsushi Sakurai

DOI： 10.1007/978-94-007-2482-2_49

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Shigenao Maruyama;Koji Matsubara;Takahiro Miura;Masud Behnia
The purpose of this paper is to consider a possibility of the independent column approximation for solving the radiative heat fluxes in a 3D turbulent channel flow. This simulation method is the simplest extension of the plane-parallel radiative heat transfer. The test case of the temperature profile was obtained from the direct numerical simulation. We demonstrate the comparison between the 3D radiative transfer simulation and the independent column approximation with an inhomogeneous temperature field and optical properties. The above mentioned results show the trivial discrepancies between the 3D simulation and the independent column approximation. The required processing time for the independent column approximation is much faster than the 3D radiative transfer simulation due to the simple algorithm. Although the independent column simulation is restricted to simple configurations such as channel flow in this paper, wide application areas are expected due to the computational efficiency.

DOI： 10.1115/1.4000240

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Koji Matsubara;Akihiko Matsui;Takahiro Miura;Atsushi Sakurai;Hitoshi Suto;Koji Kawai
Direct numerical simulation was performed for a spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel, where one wall was heated to a constant temperature and the other wall was cooled to a different constant temperature. In the simulation, fully developed flow and temperature from the straight-channel driver was passed through the inlet of the curved-channel domain. The frictional Reynolds number was assigned 150, and the Prandtl number was given 0.71. Since the flow field was examined in the previous paper, the thermal features are mainly targeted in this paper. The turbulent heat flux showed trends consistent with a growing process of large-scale vortices. In the curved part, the wall-normal component of the turbulent heat flux was twice as large as the counterpart in the straight part, suggesting active heat transport of large-scale vortices. In the inner side of the same section, temperature fluctuation was abnormally large compared with the modest fluctuation of the wall-normal velocity. This was caused by the combined effect of the large-scale motion of the vortices and the wide variation of the mean temperature
in such a temperature distribution, large-scale ejection of the hot fluid near the outer wall, which is transported into the near inner-wall region, should have a large impact on the thermal boundary layer near the inner wall. Wave number decomposition was conducted for various statistics, which showed that the contribution of the large-scale vortex to the total turbulent heat flux normal to the wall reached roughly 80% inside the channel 135° downstream from the curved-channel inlet. © 2009 Wiley Periodicals, Inc.

DOI： 10.1002/htj.20275

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

櫻井 篤;松原幸治
Radiative Properties of high temperature water vapor play an important role for radiative heat transfer analysis in combustion engineering, fire safety science, etc. Absorption spectrum of visible to infrared light inherently depends on the wavelength of electromagnetic waves. Ignoring the spectral dependence makes radiative heat transfer analyses wrong results. To overcome the problem, various nongray gas models have been proposed. However, there are a few studies for summarizing these characteristics in prediction. The goal of this study is to give valuable information for engineering applications. In the present study, radiative properties and simulation characteristics of high-temperature water vapor using the Planck-mean approximation, the statistical narrow band model, and the full-spectrum k-distribution model are assessed rigorously by comparing with the Line-by-Line method. The recent HITRAN/HITEMP databases are employed to calculate Line-by-Line spectrum.

DOI： 10.1299/kikaib.76.771_1681

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Subhash C. Mishra;Shigenao Maruyama
This article deals with the implementation of the radiation element method (REM) with the lattice Boltzmann method (LBM) to solve a combined mode transient conduction-radiation problem. Radiative information computed using the REM is provided to the LBM solver. The planar conducting-radiating participating medium is contained between diffuse gray boundaries, and the system may contain a volumetric heat generation source. Temperature and heat flux distributions in the medium are studied for different values of parameters such as the extinction coefficient, the scattering albedo, the conduction-radiation parameter, the emissivity of the boundaries, and the heat generation rate. To check the accuracy of the results, the problem is also solved using the finite-volume method (FVM) in conjunction with the LBM. In this case, the data for radiation field are calculated using the FVM. The REM has been found to be compatible with the LBM, and in all the cases, results of the LBM-REM and the LBM-FVM have been found to provide an excellent comparison.

DOI： 10.1080/10407780903583008

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Takahiro Miura;Koji Matsubara;Atsushi Sakurai
Heat transfer and fluid flow in a single-rib mounting channel were investigated by directly solving Navier-Stokes and energy equations. Flow and thermal fields were considered to be fully developed at the inlet of the channel, and the simulation was made for spatial advancement of turbulent heat transfer. Keeping the frictional Reynolds number, Re-tau 0, at 150, the rib height ratio was changed in four steps from H/delta = 0.05 to H/delta = 0.4. Computational results were confirmed to be nearly independent of grid meshes. In addition, numerical accuracy was confirmed through close agreement between computed mean pressure and the experiment by Yao et al. (1995). The numerical results revealed that the highest value of the mean Nusslet number was as large as 1.3 times the smooth surface consuming the same pumping power, and the local enhancement of heat transfer was correlated with the turbulence increase near the rib front and the reattachment point. According to the Reynolds stress budgets for H/delta = 0.2, there were mechanisms to induce powerful fluctuations: (1) Streamwise fluctuation was increased through production by flow deceleration in the upstream of the rib; (2) Redistribution to wall-normal and spanwise fluctuations was fortified by the fluid splattering to the rib front. Therefore, excellent performance of heat transfer was concluded to occur due to flow structures, which induce the strong disturbance near the rib front triggering smooth transition of the separated shear layer.

DOI： 10.1299/jtst.5.135

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Shigenao Maruyama;Koji Matsubara
The purpose of this study is to develop the radiation element method by ray emission method (REM2) code appropriate for coupling with the bioheat transfer equation, and to clarify the photothermal effect of various parameters inside biological tissues. First, the REM2, which involves the air-tissue interface effect, is validated with the existing literature. In order to clarify the effects of optical and thermophysical properties of biological tissues, a one-dimensional tissue model of CW light transport and bioheat transfer is employed. The present study provides nondimensional results, which are obtained by varying refractive index, extinction coefficient, scattering albedo, blood perfusion parameter, and conduction-radiation parameter, show valuable guidance for understanding the coupled light and bioheat transport in tissues.

DOI： 10.1080/10407782.2010.516698

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

A. Safavinejad;S. H. Mansouri;A. Sakurai;S. Maruyama
In this study, a combinatorial optimization methodology has been presented for determining the optimal number and location of equally powered heaters over some parts of the boundary, called the heater surface, to satisfy the desired heat flux and temperature profiles over the design surface while keeping the total heaters power constant but floating the number of heaters. In a typical enclosure, candidate locations were numerous for placing the heaters. The optimal number and location could be found by checking among all the possible combinations of heater power ranges and locations on the heater surface. The possibility of checking only a small portion of the total search space was increasingly desirable for finding an overall optimal solution. Micro-genetic algorithm was a candidate method which displayed a significant potential in achieving that task. Micro-genetic algorithm was used to minimize an objective function which was expressed by the sum of square errors between estimated and desired heat fluxes on the design surface. Radiation element method by ray emission model (REM(2)) Was used to calculate the radiative heat flux on the design surface. It enabled us to handle the effects of specular surfaces and blockage radiation due to enclosure geometry. The capabilities of this methodology were demonstrated by finding the optimal number and position of heaters in two irregular enclosures. The effects of refractory surface characteristics (i.e., diffuse and/or specular) on the optimal solution have been studied in detail. The results show that the refractory surface characteristics have profound effects on the optimal number and location of heaters. (C) 2008 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.applthermaleng.2008.05.025

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Isami Nitta;Shigenao Maruyama;Junnosuke Okajima;Koji Matsubara
The objective of this study is to develop a new simulator for laser therapy. In order to minimize undesired effects on the laser therapy, it is important to precisely predict for heat and photon transport inside a biological tissue. In the present study, the photon transport is solved with the Radiation Element Method by Ray Emission Model (REM2), and then coupled with bioheat transfer equation. The dimensionless results become valuable guidance for developing a laser therapy system.

DOI： 10.1299/jtst.4.314

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記述言語：日本語   掲載種別：研究論文（学術雑誌）  

松原幸治;松井暁彦;三浦貴広;櫻井篤;須藤仁;川合考治
Direct numerical simulation was performed for a spatially advancing turbulent flow and heat transfer in a two-dimensional curved channel, where one wall was heated at the constant temperature and another wall was cooled similarly. In the simulation, fully developed flow and temperature computed by the straight-channel driver was given to the inlet of curved channel domain. The frictional Reynolds number was assigned 150, and the Prandtl number was given 0.71. Since the flow field was examined in the previous paper, thermal features are mainly targeted in the present paper. Turbulent heat flux showed trends consistent with growing process of large-scale vortices. In the curved part, the wall-normal component of the turbulent heat flux was twice as large as the counterpart in the straight part, suggesting active heat transport of large-scale vortices. In the inner side of the same part, temperature fluctuation was abnormally large when compared with modest fluctuation of wall-normal velocity. This was caused by the combined effect of the large-scale motion of the vortices and the monotonous variation of the mean temperature
in such a temperature distribution, large-scale ejection of the hot fluid near the outer, which is transported into the near inner-wall region, should made large impact on thermal boundary layer near the inner wall. Wave number decomposition was made for various statistics, and such effort showed that contribution of the large-scale vortex to the total turbulent heat flux normal to the wall was roughly 80 percent at the channel center of 130° downstream from the curved-channel inlet.

DOI： 10.1299/kikaib.75.754_1336

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Shigenao Maruyama;Atsuki Komiya;Koji Miyazaki

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Shigenao Maruyama;Hirotaka Nakai;Atsushi Sakurai;Atsuki Komiya
Simplifications of the model for nongray radiative heat transfer analysis in participating media comprised of polydisperse water droplets are presented. Databases of the radiative properties for a water droplet over a wide range of wavelengths and diameters are constructed using rigorous Mie theory. The accuracy of the radiative properties obtained from the database interpolation is validated by comparing them with those obtained from the Mie calculations. The radiative properties of polydisperse water droplets are compared with those of monodisperse water droplets with equivalent mean diameters. Nongray radiative heat transfer in the anisotropic scattering fog layer, including direct and diffuse solar irradiations and infrared sky flux, is analyzed using REM2. The radiative heat fluxes within the fog layer containing polydisperse water droplets are compared with those in the layer containing monodisperse water droplets. Through numerical simulation of the radiative heat transfer, polydisperse water droplets can be approximated by using the Sauter diameter, a technique that can be useful in several research fields, such as engineering and atmospheric science. Although this approximation is valid in the case of pure radiative transfer problems, the Sauter diameter is reconfirmed to be the appropriate diameter for approximating problems in radiative heat transfer, although volume-length mean diameter shows better accordance in some cases. The CPU time for nongray radiative heat transfer analysis with a fog model is evaluated. It is proved that the CPU time is decreased by using the databases and the approximation method for polydisperse particulate media. (C) 2007 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jqsrt.2007.05.006

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Ali Safavinejad;Shigenao Maruyama;Seyed Hossein Mansouri;Atsushi Sakurai
This study presents an optimization methodology for finding the heaters setting that produce a desired heat flux and temperature distribution over a region of the enclosure surface, called the design surface. Radiation element method by ray emission model (REM2) was used to calculate the radiative heat flux on the design surface, which enable us to handle reflecting surfaces. Micro-genetic algorithm was used to minimize an objective function, which was expressed by the sum of square error between estimated and desired heat fluxes on the design surface. The novel features of this methodology were demonstrated by finding the optimal heaters setting of a three dimensional enclosure for three aspect ratio. The effects of refractory properties have been studied as well.

DOI： 10.1299/jtst.3.179

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Shigenao Maruyama;Atsushi Sakurai;Atsuki Komiya
A new algorithm, the discrete ordinates radiation element method (DOREM), for modeling radiative heat transfer in inhomogeneous three-dimensional participating media is described. The DOREM uses advantages of the both the radiation element method (REM) and the discrete ordinates method. Benchmark comparisons are conducted against several radiation models. The DOREM successfully implements radiative heat transfer simulations precisely, since false scattering never occurs. The DOREM has advantages of computational speed against Monte Carlo, and the CPU time and the memory size of the DOREM are 82 times faster and 767 times smaller at the maximum than that of the REM.

DOI： 10.1080/10407790600878726

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

A Sakurai;S Maruyama;S Sakai;T Nishikawa
The effects of three-dimensional (3D) radiative heat transfer in cloud fields are investigated by using the radiation element method by ray emission model (REM2). We have performed a 3D radiative heat transfer simulation in two fair-weather cumuli that are subjected to solar and sky irradiation. One of the features in this simulation is that both shortwave radiation and longwave radiation are considered. As a result, the effect of shortwave radiation is not so substantial as compared with that of longwave radiation in terms of the heat generation rate within the cloud. Also, the radiative interaction does not strongly affect the relative differences of the average heat generation rate between the single cloud model and the double cloud model. However, the distributions of heat generation rate at the thin layer beneath the cloud surface are influenced by radiative interaction and shadowing effect. Hence, these effects caused by 3D radiative heat transfer are important for horizontal inhomogeneous cloud fields. (C) 2004 Elsevier Ltd. All rights reserved.

DOI： 10.1016/j.jqsrt.2004.08.013

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記述言語：英語   掲載種別：研究論文（学術雑誌）  

Atsushi Sakurai;Tae-Ho Song;Shigenao Maruyama;Hyun Keol Kim
This paper compares and scrutinizes the characteristics of radiation element method by ray emission model (REM2) and discrete ordinates interpolation method (DOIM). A three-dimensional radiative heat transfer problem is solved within a rectangular enclosure containing absorbing, emitting, nonscattering medium with temperatures given as a sine function. The calculation results are validated with the zonal results and the analytical solution. Generally, the calculation results agree well with the exact solution. However, when the optically thickness is much larger than unity, the zonal and REM2 results overestimate the heat source strength and wall heat flux, and when it is small, DOIM results underestimate them. The reasons and remedies are carefully discussed.

DOI： 10.1299/jsmeb.48.259

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担当区分：筆頭著者  

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担当区分：筆頭著者  

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担当区分：筆頭著者  

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記述言語：英語  

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

We numerically demonstrate wavelength-selective absorption in core-shell deposited on top of a continuous Au film by excitation of magnetic resonance. The resonance of magnetic polariton at wavelength 653 nm is confirmed by electromagnetic Geld distribution. The influences of Au core diameter, SiO_2 shell thickness on the resonance wavelength are studied with 3D finite-differential time-domain (FDTD) method. The fundamental study will facilitate the development of a core-shell metamaterial for energy and sensing applications.

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

Direct numerical simulation was performed for a spatially advancing turbulent flow in a two-dimensional curved channel. The radius ratio of the curved part, α , was set at 0.92, the same as Kobayashi et al.'s experiment. And the friction Reynolds number, Re_<τ0>, was set at 550. Numerically solved mean velocity field showed trends consistent with the experiment. As a result, the validity of the simulation was confirmed. Instantaneous flow field implied that micro-scale structures near the outer wall were related to the birth and growth of large-scale vortices.

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記述言語：日本語   出版者・発行元：公益社団法人日本工学教育協会  

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

It's necessary to further improve technology of energy-saving with increasing energy consumption. And there is a current situation that low-temperature exhaust heat has been discarded from a factory. So we have started a study of the heat pipe for utilizing this exhaust heat. It's necessary to carry out heat transportation of long distance and high density for utilizing the exhaust heat. Therefore the present study had been used the loop thermosyphon. But quantities of the water which are enclosed in loop thermosyphon will affect heat transportation. So the present study has been practiced the experiment which had been changed quantities of the water and thermal dose. And we have researched the effect of heat transportation. As the result, heat transportation is improved with increasing thermal dose.

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

An experimental study was performed for freeze-concentration of 1 % water-solution of sodium chloride in a cylindrical container, where a heat transfer pipe was set vertically. Experimental results denoted that temperature gradient in the ice promote solute rejection. When the ice is given a temperature gradient for long time , solute is eliminated little by little from the ice . By varying the temperature of the inner wall, the difference of concentration rate, distribution coefficient and concentration of ice was measured.

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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記述言語：英語  

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

Direct numerical simulation was performed for a spatially advancing turbulent flow in a two-dimensional curved channel. The radius ratio of the curved part, α, was set at 0.92, the same as Kobayashi et al.'s experiment. And the friction Reynolds number, Re_<τ0>, was set at 550 and 300. Numerically solved mean velocity field showed trends consistent with the experiment. As a result, the validity of the simulation was confirmed. Instantaneous flow field implied that micro-scale structures near the outer wall were related to the birth and growth of large-scale vortices.

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記述言語：英語   出版者・発行元：一般社団法人日本機械学会  

Direct numerical simulation was performed for a spatially advanced turbulent flow in a two-dimensional curved channel. In the past research, the influence of radius ratio was not discussed. Therefore, the radius ratio of the curved part, a=0.92, the same as Kobayashi et al.'s experiment, and 0.8 were calculated. Then, we carried out simulations of the temperature condition where two walls were sustained at different temperatures. Prandtl number was assumed to be 0.71. Analogy between the friction factor and the Stanton number was confirmed through computed cases. Turbulence statistics including the turbulent heat flux budgets were presented and discussed.

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記述言語：日本語   出版者・発行元：一般社団法人日本機械学会  

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記述言語：日本語   出版者・発行元：公益社団法人 日本工学教育協会  

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開催年月日： 2019年7月

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開催年月日： 2019年4月

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開催年月日： 2019年1月

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受賞区分：国内学会・会議・シンポジウム等の賞  受賞国：日本国

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受賞国：日本国

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受賞区分：国内学会・会議・シンポジウム等の賞  受賞国：日本国

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受賞区分：国内学会・会議・シンポジウム等の賞  受賞国：日本国

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受賞国：日本国

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受賞区分：国内学会・会議・シンポジウム等の賞  受賞国：日本国

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