詳細

道岡　武信 （ミチオカ　タケノブ）

  • 理工学部 機械工学科　教授
Last Updated :2024/04/25

コミュニケーション情報 byコメンテータガイド

  • コメント

    化学反応装置などの機械装置内や環境中の流れ場などにおける流れ・熱・物質の詳細な挙動を解明およびモデル化し、産業界に役立つ実用的な数値モデルを開発する研究を行っています。

研究者情報

学位

  • 博士（工学）（京都大学）

ホームページURL

科研費研究者番号

  • 20371370

J-Global ID

研究キーワード

  • 数値シミュレーション   乱流構造   都市防災   都市キャニオン   風洞実験   ガス拡散   大気拡散   

現在の研究分野（キーワード）

    化学反応装置などの機械装置内や環境中の流れ場などにおける流れ・熱・物質の詳細な挙動を解明およびモデル化し、産業界に役立つ実用的な数値モデルを開発する研究を行っています。

研究分野

  • 社会基盤（土木・建築・防災） / 建築環境、建築設備
  • ものづくり技術（機械・電気電子・化学工学） / 流体工学

経歴

  • 2015年04月 - 現在  近畿大学 理工学部 機械工学科Faculty of Science and Engineering, Department of Mechanical Engineering
  • 2001年04月 - 2015年03月  一般財団法人電力中央研究所
  • 2012年04月 - 2013年03月  九州大学 工学部 非常勤講師School of Engineering
  • 2006年04月 - 2011年03月  東京工業大学大学院環境理工学創造専攻連携准教授
  • 2006年10月 - 2007年09月  カリフォルニア大学バークレイ校客員研究員

学歴

  • 1998年04月 - 2001年03月   京都大学大学院   工学研究科 機械工学専攻   博士後期課程
  • 1996年04月 - 1998年03月   九州大学大学院   工学研究科 化学機械工学専攻   修士課程
  • 1993年04月 - 1996年03月   九州大学   工学部   化学機械工学科

所属学協会

  • 土木学会   日本建築学会   化学工学会   大気環境学会   日本流体力学会   日本機械学会   

研究活動情報

論文

  • Takenobu Michioka; Ryo Funaki; Takumi Kawai
    BOUNDARY-LAYER METEOROLOGY 2023年01月 [査読有り]
     
    Large-scale turbulent motions at a streamwise street coupled with spanwise motion in a canyon have been observed within an idealized urban canopy, but the effects of building array geometry on large-scale turbulent motions within the canopy remain unresolved. To address this issue, large eddy simulation is performed for the canyon width of 0.5 H-1.5 H (H = cube height) and the street width of H-1.5 H. In the case of a large canyon with (1.5 H) and a large street width (1.5 H), large-scale turbulent motions are observed at the streamwise street. However, large-scale turbulent motions are not generated in the case of a small canyon width (0.5 H). The size of the canyon or street width affects the generation of the large-scale turbulent motions. When a pair of the high- and low-momentum motions are present at the adjacent intersection pathways under the generation of the large-scale turbulent motions, large-scale streamwise vortices are occasionally generated. These streamwise vortices maintain the generation of large-scale turbulent motions.
  • Takenobu Michioka
    Environmental Fluid Mechanics 2022年06月 [査読有り]
  • Takumi Sato; Yusei Kobayashi; Takenobu Michioka; Noriyoshi Arai
    SOFT MATTER 17 15 4047 - 4058 2021年04月 [査読有り]
     
    In this study, a coarse-grained molecular simulation was performed to investigate the morphologies and phase diagrams of self-assembled polymer-tethered nanoparticles (NPs) confined in nanotubes (NTs). Unlike ordinary NPs, polymer-tethered NPs have two distinct characteristic lengths, which are key factors that determine their self-assembly. Herein, two distinct types of NT walls and three types of polymer-tethered NPs were considered: hydrophilic and hydrophobic walls, and hydrophilic, hydrophobic, and Janus surfaces. First, the qualitative phase diagrams of the axial pressure, P-z, versus the ratio of the NT radius to the NP radius, L, were derived. The results revealed that diverse self-assembled morphologies, which are not formed in non-tethered NPs, were observed in the polymer-tethered NPs. For example, three types of ordered structures with different structural characteristic lengths, depending on P-z, were obtained. In addition, the effect of the chemical nature of the polymer-tethered NP surface on the self-assembled morphology confined in NTs was investigated. Clusters of water molecules were formed, particularly in the hydrophobic polymer-tethered NPs, and these clusters caused the structural distortion of the NP. Moreover, in the polymer-tethered NPs with the Janus amphiphilic surface, the hydrophobic and hydrophilic polymer tethered NPs assembled in the axial direction to form an ordered structure, and a double-helix structure was formed at L = 3.0 in the hydrophobic NT. The results of these simulations indicate that the self-assembly behaviours of polymer-tethered NPs can be qualitatively predicted based on the chemical nature of the NT walls and the surface design of the polymer-tethered NP.
  • 林 将史; 道岡 武信
    大気環境学会誌 55 3 116 - 124 公益社団法人 大気環境学会 2020年 [査読有り]
     

    近年、電力自由化に伴い、既設の風力発電所近くに火力発電所が建設される事例があり、周辺地域への影響が懸念されている。風車によるガス拡散への影響については簡易モデルで検討されている例はあるが、風洞実験や数値シミュレーションなどで風車後流域を考慮した検討は実施されていない。本研究では風車の風下側および風上側にガスの放出源がある場合の風車後流域の排ガス拡散挙動を数値シミュレーションにより検討した。ガス放出点が風車風上に位置する場合、ガスの放出点の高さの違いにより風車がガス拡散に及ぼす影響度が変化することがわかった。ガス放出点が風車ハブ高さと同じ高さに位置する場合、風車後方でガスは風車ブレード長さ程度まで一様に拡散し、地表付近でのガス濃度が高くなる。ガス放出点が風車ブレードの上端付近に位置する場合、風車近傍で風車ハブ高さよりも低い高さまでガスが拡散され、風下に行くにつれガスは地表付近まで拡散され、風車遠方位置において地表面付近のガス濃度が高くなる。ガス放出点が風車ブレードの上端よりも上に位置する場合、風車風下で風車回転によるガス拡散挙動への影響は小さい。一方、ガス放出点が風車風下に位置する場合、ガス拡散範囲、ガス濃度ともに風車有無に関わらず、同じ傾向を示し、風車による影響は小さいことがわかった。

  • Suzuki Naoya; Michioka Takenobu; Konda Masanori; Kutsuwada Kunio; Masuda Yuji
    Journal of Advanced Marine Science and Technology Society 25 1 1 - 14 海洋理工学会 2019年 [査読有り]
     
    <p>Generally, the air-sea momentum, heat, and CO<sub>2</sub> gas flux are calculated in field observation using the eddy correlation method, which simultaneously measures the horizontal and vertical wind components. Measuring the components of wind velocity is usually limited to fixed installations owing to the minor effect of the platform on the wind flow. Occasionally, numerical simulations are sometimes used for shipboard observations. However, the details of the effect of the wind flow around an observation ship are scarcely investigated using numerical simulations, although ships affect the wind flow and wind direction by wind distortion. In this study, we investigated the effect of ships on the wind flow around the Hakuho–Maru of the Japan Agency for Marine-Earth Science and Technology using a numerical simulation. As a result of the flow visualization, measuring the horizontal and vertical components of wind velocity was very difficult because the wind distortion (upward and downward gusts, among others) was very large owing to the effect of the ship. This showed that the effect of the ship was significant for the measurements of air-sea momentum, heat, and CO<sub>2</sub> gas flux.</p>
  • Takenobu Michioka; Hiroshi Takimoto; Hiroki Ono; Ayumu Sato
    Boundary-Layer Meteorology 2019年01月 [査読有り]
     
    © 2019, Springer Nature B.V. Large-eddy simulation of turbulent flow and gas dispersion in a cubical canopy is used to investigate the effect of wind-direction fluctuations on gas dispersion. Square blocks are set at regular intervals on the bottom surface, with line sources placed within the first, second, third, fifth and seventh rows. Large-eddy simulation without wind-direction fluctuations produces a good prediction of the mean streamwise velocity component, and the standard deviations of the fluctuations in the streamwise and spanwise velocity components, obtained from a wind-tunnel experiment. Wind-direction fluctuations marginally affect the mean streamwise velocity component above the canopy in the first row, and do not significantly affect the component beyond the third row. The standard deviations of the fluctuations in the streamwise and spanwise velocity components above the canopy are also affected by wind-direction fluctuations, but within the canopy the components are less sensitive to the fluctuations beyond the third row. The spatially-averaged concentrations within the canyon with wind-direction fluctuations before the third row are marginally greater than concentrations without the fluctuations, but they are essentially identical beyond the fifth row. The low-frequency turbulent flow that passes through the canyon is generated with and without wind-direction fluctuations.
  • 瀧本 浩史; 小野 浩己; 佐藤 歩; 道岡 武信
    日本風工学会論文集 44 3 59 - 67 一般社団法人 日本風工学会 2019年 [査読有り]
     
    When a stack in industrial facilities is not sufficiently high compared to the surrounding buildings, the dispersion of discharged pollutants can be affected by the buildings; this is commonly termed as building downwash. To enable more precise prediction of the building downwash, we have developed a computational fluid dynamics model that can reproduce momentum plume-rise process. We confirmed that the most of the surface concentrations predicted using the proposed model are within a factor of two of the wind-tunnel experimental results. Our study suggests that the mesh types around a stack can affects the prediction of surface concentration in high wind speed conditions.
  • Takenobu Michioka
    International Journal of Heat and Mass Transfer 125 569 - 579 2018年10月 [査読有り]
     
    Large-eddy simulation is implemented for turbulent flow and gas dispersion over wavy walls across a wide range of the wave amplitude to wavelength ratio (α = 1.0, 1.5, and 2.0). Two tracer gases are emitted from point sources located at a single crest and trough of the wavy wall. Because the values of α increase under the Reynolds number based on the bulk velocity and the wavelength is 6.67×104, the flow separates behind the crest and the standard deviations of the fluctuation in streamwise and spanwise velocity components become relatively large especially at the upslope of the wavy wall. The increase are related to the vortices linked to the Görtler instability mechanism. The change in the flow pattern with respect to the value of α significantly affects the gas dispersion within the valley. As the Reynolds number increases under the wavy wall with α = 2.0, the flow tends to follow the bottom surface of the wavy wall and the number of the vortices increases at the upslope, but the vortices do not significantly affect the gas dispersion over the wavy wall.
  • Takenobu Michioka; Hiroshi Takimoto; Hiroki Ono; Ayumu Sato
    Boundary-Layer Meteorology 168 1 - 21 2018年03月 [査読有り]
     
    The effects of fetch on turbulent flow and pollutant dispersion within a canopy formed by regularly-spaced cubical objects is investigated using large-eddy simulation. Six tracer gases are simultaneously released from a ground-level continuous pollutant line source placed parallel to the spanwise axis at the first, second, third, fifth, seventh and tenth rows. Beyond the seventh row, the standard deviations of the fluctuations in the velocity components and the Reynolds shear stresses reach nearly equivalent states. Low-frequency turbulent flow is generated near the bottom surface around the first row and develops as the fetch increases. The turbulent flow eventually passes through the canopy at a near-constant interval. The mean concentration within the canopy reaches a near-constant value beyond the seventh row. In the first and second rows, narrow coherent structures frequently affect the pollutant escape from the top of the canopy. These structures increase in width as the fetch increases, and they mainly affect the removal of pollutants from the canopy.
  • T. Michioka; H. Takimoto; H. Ono; A. Sato
    Asian Journal of Atmospheric Environment 11 4 270 - 282 2017年12月 [査読有り]
     
    To evaluate the deposition amount on a ground surface, mesoscale numerical models coupled with atmospheric chemistry are widely used for larger horizontal domains ranging from a few to several hundreds of kilometers however, these models are rarely applied to high-resolution simulations. In this study, the performance of a dry and wet deposition model is investigated to estimate the amount of deposition via computational fluid dynamics (CFD) models with high grid resolution. Reynolds-averaged Navier-Stokes (RANS) simulations are implemented for a cone and a two-dimensional ridge to estimate the dry deposition rate, and a constant deposition velocity is used to obtain the dry deposition flux. The results show that the dry deposition rate of RANS generally corresponds to that observed in wind-tunnel experiments. For the wet deposition model, the transport equation of a new scalar concentration scavenged by rain droplets is developed and used instead of the scalar concentration scavenged by raindrops falling to the ground surface just below the scavenging point, which is normally used in mesoscale numerical models. A sensitivity analysis of the proposed wet deposition procedure is implemented. The result indicates the applicability of RANS for high-resolution grids considering the effect of terrains on the wet deposition.
  • Takenobu Michioka; Hiroshi Takimoto; Hiroki Ono; Ayumu Sato
    BOUNDARY-LAYER METEOROLOGY 164 3 401 - 418 2017年09月 [査読有り]
     
    Large-eddy simulation is used to investigate the Reynolds-number dependence of gas dispersion over a wavy wall, because the Reynolds-number dependence is important for reproducing normal flow and gas dispersion in a wind tunnel. The ratio of amplitude to wavelength of the wavy surface is set to 0.1, and the Reynolds number based on the bulk velocity and the channel height is varied from to . Two tracer gases are emitted from point sources located at a single crest and trough of the wavy wall. For the lowest Reynolds number, the flow over the wavy wall separates behind the crest and reattaches to the upslope. A recirculation zone is observed near the trough, and the gas emitted from the trough is transported upwind by the recirculating reverse flow. Some gas is discharged from the valley by intermittent velocity bursts that originate in the recirculation zone. As the Reynolds number is increased, the recirculation zone shrinks and the flow increasingly follows the wavy wall. The gas generally disperses in the forward direction and is discharged by the advective flow. As for the gas emitted from the crest, this disperses with the separating flow, while some gas is trapped within the recirculation zone at the lower Reynolds number. As the Reynolds number is increased, the gas advection increasingly follows the wavy wall and the height of the peak concentration approaches the wavy wall. In addition, the accumulated concentration within the valley in both sources depends strongly on the Reynolds number.
  • 小野浩己; 瀧本浩史; 佐藤歩; 道岡武信; 道岡武信; 佐田幸一
    大気環境学会誌 52 1 19‐29 - 29 公益社団法人 大気環境学会 2017年01月 [査読有り]
     

    地熱発電所の環境アセスメントにて実施される硫化水素の大気拡散予測評価の期間短縮および費用削減を目的として、従来行われている風洞実験の代替として用いることのできる3次元数値モデルを開発した。

    地熱発電所の冷却塔から放出される硫化水素の大気拡散評価を行うためには、冷却塔からの排気上昇過程、周辺建屋による拡散への影響、周囲の地形による拡散への影響を的確に再現できる必要がある。そのため、これらの現象を高精度に再現可能と期待されるラージ・エディ・シミュレーション (LES) をベースとした数値モデル構築を行い、さらに、LESに適した格子生成プログラムを開発した。

    また、開発した数値モデルの予測精度検証のため、実際の地熱発電所を想定した風洞実験を行った。風洞実験との比較の結果、開発した数値モデルは風洞実験で得られた地表濃度の傾向を精度よくとらえられており、環境アセスメントで重要となる最大着地濃度に関しては、すべてのケースで風洞実験結果の0.5～2.0倍以内に収まる結果となった。これらの結果から、開発した数値モデルは地熱発電所環境アセスメントの硫化水素拡散予測に十分適用可能であると結論づけられた。

  • 鈴木直弥; 早稲田卓爾; 道岡武信; 辰巳公亮; 竹本剛志
    海洋理工学会誌(Web) 23 1 11‐19(J‐STAGE)  2017年 [査読有り]
  • Takenobu Michioka; Hiroshi Takimoto; Hiroki Ono; Ayumu Sato
    BOUNDARY-LAYER METEOROLOGY 160 1 185 - 199 2016年07月 [査読有り]
     
    Large-eddy simulation is conducted to investigate the effect of fetch on the pollutant-removal mechanism from a two-dimensional street canyon with a building-height to street-width (aspect) ratio of 1. The line sources were placed within the first, second, third, fifth, seventh and tenth canyons, and the six tracer gases are simultaneously released by a ground-level continuous pollutant line source placed parallel to the spanwise axis at the canyons. The mean concentration and the deviation of the concentration fluctuation within the canyon roughly reach a near-constant value downwind of the seventh canyon, which is similar to the behaviour of the turbulent intensities. In the first canyon, pollutant removal is affected by both advective flow and turbulent flow; however, the turbulent motions mainly affect pollutant removal from the top of the canyon as the fetch increases. In the first and third canyons, the low-momentum fluid does not always affect pollutant removal, but does so gradually as the fetch increases.
  • 小野浩己; 瀧本浩史; 道岡武信; 佐藤歩; 佐田幸一
    大気環境学会誌 51 3 161 - 173 公益社団法人 大気環境学会 2016年05月 [査読有り]
     

    近年、任意の格子形状を扱えるCFDソフトウェアが台頭してきたことにあわせ、表面形状が複雑な物体に対しても多面体格子を自動的に配置することで柔軟に計算格子を生成することのできるシステムが多数開発されている。しかし、これらのシステムによって生成された格子を地形上の流れや汚染質拡散のラージエディシミュレーション（LES）に用いた例はほとんどなく、その適用可能性は不明である。そこで、本研究では単純地形上の流れおよび拡散を対象に、これらのシステムによって生成された格子を用いた計算を行い、これまで地形上流れの計算で多く用いられていた直交曲線座標系格子との比較を行った。風洞実験の結果との比較によりLESの再現精度について検討した結果、地表面付近の格子形状によって地形からの剥離気流の性状が変化することを明らかにし、地形周りの平均速度・乱流統計量および汚染質濃度を精度よく再現するには、地表面近傍の格子を地表面形状および流れ方向に沿わせることが必要であることを示した。

  • Kazutaka Takata; Takenobu Michioka; Ryoichi Kurose
    ATMOSPHERE 7 4 2016年04月 [査読有り]
     
    Heated moist air from a cooling tower forms a visible plume and needs to be predicted, not only for the performance design of the cooling tower, but also for environmental impact assessments. In this study, a computational fluid dynamics analysis is conducted to predict the scale of a visible plume rising from a cross flow cooling tower with mechanical draft (provided by a rotating fan). The results of computational fluid dynamics analysis are verified by comparing predictions with an actual observed plume. The results show that the predicted visible plume represents the observed plume in an error range of 15%-20%, which is permissible for designing a cooling tower. Additionally, the mixing condition of heated dry air and moist air under dry and wet combined operation is examined, and the condition is thought to affect the scale of the visible plume. It is found that, in the case of a mechanical-draft cooling tower, the fan has a mixing function which performs the complete mixing of wet and dry air, and this suggests that the generation of the plume can be determined by the intersection of the operation line and saturation line. Additionally, the effect of external wind on the scale of the visible plume is large, especially for dry and wet combined operation.
  • Takenobu Michioka; Koichi Sada; Kazuki Okabayashi
    ATMOSPHERE 7 4 2016年04月 [査読有り]
     
    Wind-tunnel experiments were conducted to evaluate the effect of additional structure (building, sea wall and banking) on the effective stack height, which is usually used in safety analyses of nuclear power facilities in Japan. The effective stack heights were estimated with and without the additional structure in addition to the reactor building while varying several conditions such as the source height, the height of additional structure and the distance between the source position and the additional structure. When the source height is equivalent to the reactor building height, the additional structure enhances both the vertical and horizontal gas dispersion widths and decreases the ground gas concentration, and it means that the additional structure does not decrease the effective stack height. When the source height is larger than the reactor height, the additional structures might affect the effective stack height. As the distance between the source and the additional structure decreases, or as the height of the additional structure increases, the structure has a larger effect on the effective stack height.
  • 瀧本浩史; 小野浩己; 佐藤歩; 道岡武信; 佐田幸一
    大気環境学会誌 50 5 226 - 232 2015年09月 [査読有り]
  • 小野浩己; 瀧本浩史; 道岡武信; 佐藤歩
    日本建築学会環境系論文集 80 718 1143 - 1151 2015年 [査読有り]
     
    Validation of Large Eddy Simulation based on a Finite Volume Method was undertaken using data from our previous experiment. Four schemes for convection-term discretization were tested on a momentum transport equation, a passive scalar transport equation and an active scalar transport equation. The results support the use of a low-dissipation scheme for the momentum transport equation to avoid overestimating circulation on a rooftop. Such overestimation of circulation can lead to an underestimation of concentrations behind the building. Conversely, a bounded scheme, even in cases that resulted in excess numerical dissipation, is preferred for each scalar transport equation to maintain a profile and peak concentration value.
  • 小野 浩己; 瀧本 浩史; 道岡 武信
    日本建築学会環境系論文集 79 701 607 - 613 日本建築学会 2014年07月 [査読有り]
     
    Wind tunnel experiments were carried on the concentration fields with rooftop exhaust under neutral and stably stratified flow. Mean velocity distribution behind the building was not affected by atmospheric stability, nevertheless turbulence intensity and contaminant distribution became quite different. Partial spread width was estimated with assuming Gaussian distribution therefore it was found that strength of thermal stratification behind the building was attenuated locally by wake from the building.
  • Takenobu Michioka; Hiroshi Takimoto; Ayumu Sato
    BOUNDARY-LAYER METEOROLOGY 150 2 259 - 275 2014年02月 [査読有り]
     
    Large-eddy simulations were conducted to investigate the mechanism of pollutant removal from a three-dimensional street canyon. Five block configurations with aspect ratios (building height to length) of 1, 2, 4, 8 and were used to create an urban-like array. A pollutant was released from a ground-level line source at the centre of the target canyon floor. For smaller aspect ratios, the relative contribution of the turbulent mass flux to net mass flux at the roof level, which was spatially averaged along the roof-level ventilation area, was closer to unity, indicating that turbulent motions mainly affected pollutant removal from the top of the canyon. As aspect ratio increased, the relative contribution became smaller, owing to strong upwind motions. However, the relative contribution again reached near unity for the infinite aspect ratio (i.e. a two-dimensional street canyon) because of lowered lateral flow convergence. At least 75 % of total emissions from the three-dimensional street canyon were attributable to turbulent motions. Pollutant removal by turbulent motions was related to the coherent structures of low-momentum fluid above the canyons. Though the coherent structure size of the low-momentum fluid differed, the positions of low-momentum fluid largely corresponded to instantaneous high concentrations of pollutant above the target canyon, irrespective of canyon geometry.
  • 丹野 賢二; 野田 直希; 山本 融; 黒瀬 良一; 道岡 武信; 牧野 尚夫
    粉体工学会誌 50 10 733 - 740 The Society of Powder Technology, Japan 2013年10月 [査読有り]
     
    In coal-fired power plants, selective catalytic de-NOx systems are widely used and offer a very efficient method to reduce NOx emissions from such plants. However, de-NOx catalyst degrades in long-term operation and catalysts must be periodically exchanged. Exchange of catalysts costs a great deal, hence there is a strong economic incentive to elucidate the degradation mechanism of catalysts and optimize the operation conditions of de-NOx equipment. In this study, fluorescent X-ray analysis is performed to investigate the elemental distribution on the catalyst surface. Also, X-ray absorption fine structure (XAFS) analysis is applied to determine the chemical form of Vanadium in the catalyst. The results show that elements found in fly ash are detectable in the upstream region near the inlet, whereas such elements are not detected in the downstream region near the outlet. This tendency is in good qualitative agreement with the author's previous numerical result. Vanadium in the fresh catalyst is mainly in its 3+ valence state, whereas that in used catalyst is mainly in the 4+ or 5+ valence states. The ratio of vanadium in 5+ valence state is larger in the inlet region than in the downstream region. This is due to turbulent eddy mixing which promotes vanadium oxidation in the inlet region.
  • Kenji Tanno; Ryoichi Kurose; Takenobu Michioka; Hisao Makino; Satoru Komori
    ADVANCED POWDER TECHNOLOGY 24 5 879 - 885 2013年09月 [査読有り]
     
    Selective catalytic reaction is a very efficient method to reduce NOx emissions from thermal power plants and is widely used in Japan. To develop a higher performance de-NOx system and optimize its maintenance schedule, it is important to understand the NOx reduction mechanism in the honeycomb channel which supports the de-NOx catalysts. In this study, the effects of duct channel flow behavior on the de-NOx, reaction at the catalyst surface were investigated using a direct numerical simulation (DNS). The DNS computations were performed for three inflow conditions, one laminar and two turbulent. The results show that although the flow transitions from turbulent to laminar flow as the flow moves downstream for the turbulent inflow conditions, de-NOx reaction rates for the turbulent inflow conditions are higher than that for the laminar inflow condition even in the downstream region. This is because of the remaining cross-sectional fluid motions caused by the inflow turbulence. As a result, de-NOx efficiencies for the turbulent conditions are higher than that for the laminar case. For both laminar and turbulent inflow conditions, de-NOx reaction is suppressed in the corner regions due to the flow stagnation. (C) 2013 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.
  • T. Michioka; A. Sato; K. Sada
    ATMOSPHERIC ENVIRONMENT 75 153 - 162 2013年08月 [査読有り]
     
    A microscale large-eddy simulation (LES) model coupled to a mesoscale LES model is implemented to estimate a ground concentration considering the meteorological influence in an actual urban district. The microscale LES model is based on a finite volume method with an unstructured grid system to resolve the flow structure in a complex geometry. The Advanced Regional Prediction System (ARPS) is used for mesoscale meteorological simulation. To evaluate the performance of the LES model, 1-h averaged concentrations are compared with those obtained by field measurements, which were conducted for tracer gas dispersion from a point source on the roof of a tall building in Tokyo. The concentrations obtained by the LES model without combing the mesoscale LES model are in quite good agreement with the wind-tunnel experimental data, but overestimates the 1-h averaged ground concentration in the field measurements. On the other hand, the ground concentrations using the microscale LES model coupled to the mesoscale LES are widely distributed owing to large-scale turbulent motions generated by the mesoscale LES, and the concentrations are nearly equal to the concentrations from the field measurements. (C) 2013 Elsevier Ltd. All rights reserved.
  • Hiroshi Takimoto; Atsushi Inagaki; Manabu Kanda; Ayumu Sato; Takenobu Michioka
    Boundary-Layer Meteorology 147 2 217 - 236 2013年05月 [査読有り]
     
    We examine the similarity of turbulent organized structures over smooth and very rough wall flows. Turbulent flow fields in horizontal cross-sections were measured using particle image velocimetry, and the characteristics of turbulent organized structures over four types of surfaces were investigated. Measurements were conducted at several measurement heights across the internal boundary layer. The length and width of turbulence structures were quantified using a two-point correlation method. We selected two thresholds of two-point correlation coefficients to consider both large-scale and small-scale structures the validity of these choices was examined through the analyses using proper orthogonal decomposition. For large-scale structures, the length and aspect ratios (streamwise length/spanwise width) of structures were highly correlated with the velocity gradient for each measurement height and boundary-layer thickness. This relationship was also examined in the results of previous studies, and the scaling of the aspect ratio with the non-dimensional velocity gradient again showed the importance of the velocity gradient, with slight differences found between smooth and rough surfaces. In contrast, the small-scale structures exhibited weak dependency on the velocity gradient and boundary-layer thickness. Instantaneous snapshots of turbulent organized structures at the same shear level also displayed differences in small-scale structures, but the structures of the organized motions resembled each other, as in the results of the two-point correlation method. © 2012 Springer Science+Business Media Dordrecht.
  • 丹野 賢二; 黒瀬 良一; 道岡 武信; 牧野 尚夫; 小森 悟
    粉体工学会誌 50 3 204 - 211 The Society of Powder Technology, Japan 2013年03月 [査読有り]
     
    In coal-fired thermal power plants, selective catalytic de-NOx system is widely used and very efficient method to reduce NOx emission from the plant. However, ash particles laden in flue gas adhere on a de-NOx catalyst surface, and ash coverage causes the severe degradation of de-NOx catalyst. Authors numerically investigated the effect of flow behavior in a honeycomb channel on the adhesion characteristics of particles to the wall in the previous study. However, previous study was performed under the assumption that all particles, which reach the wall, adhere. Therefore, in this study, the effect of particle collision and rebound behavior on the adhesion characteristics on the wall of honeycomb shaped catalyst was investigated by applying a direct numerical simulation (DNS). In order to take account of particle collision and rebound behavior, the probability coefficient of adhesion was introduced. The results show that although particle adheres on the wall only in the upstream region, in which flow condition is turbulent, irrespective of adhesion probability coefficient, the amount of adhered particles decreases with decreasing probability coefficient. The results also indicate that particle re-adhesion also occurs only in the upstream region even though some particle rebound and return to the flow from the wall.
  • Takenobu Michioka; Ayumu Sato
    BOUNDARY-LAYER METEOROLOGY 145 3 469 - 484 2012年12月 [査読有り]
     
    Large-eddy simulations are conducted to investigate the effects of the incoming turbulent structure of the flow on pollutant removal from an ideal canyon. The target canyon is a two-dimensional street canyon with an aspect ratio of 1.0 (building height to street width). Three turbulent flows upwind of the street canyon are generated by using different block configurations, and a tracer gas is released as a ground-level line source at the centre of the canyon floor. Mean velocity profiles for the three flows are similar, except near the roof. However, the root-mean-square values of the velocity fluctuations and the Reynolds shear stress increase with the friction velocity of the incoming turbulent flow. The spatially-averaged concentration within the canyon decreases with increasing friction velocity. Coherent structures of low-momentum fluid, generated above the upwind block configurations, contribute to pollutant removal, and the amount of pollutant removal is directly related to the size of the coherent structure.
  • 佐田 幸一; 佐藤 歩; 道岡 武信; 市川 陽一
    大気環境学会誌 = Journal of Japan Society for Atmospheric Environment 47 6 261 - 269 大気環境学会 2012年11月 [査読有り]
     
    火力発電所の環境アセスメントでは排ガス拡散の地形影響評価に三次元数値モデルが使用されている。近年、火力発電所の設備更新時には、航空法の遵守や景観への配慮に加えて、高効率発電システムの導入や燃料転換により環境負荷が大幅に低減されることから、従来よりも煙突高さを低くするケースが見られる。本論文では数値モデルを低煙突に適用できるように、非静力学モデルや地表付近の乱流量を経験的に修正する方法の導入をはかった。また、将来の地表面付近の低い煙突からの排ガス拡散予測への適用に先立ち、本論文では火力発電所の高所煙源を対象に本論文の数値モデルと現行の数値モデルの整合性を確認した。その結果、地表煙軸濃度分布は風洞実験で得られた地形による地表煙軸濃度分布の変化をほぼ再現できることが示されるとともに、環境アセスメントの評価項目である最大着地濃度比や最大着地濃度距離比は現行の数値モデルと同程度の予測精度が得られることが確認できた。
  • 丹野 賢二; 黒瀬 良一; 道岡 武信; 牧野 尚夫; 小森 悟
    粉体工学会誌 49 10 738 - 744 The Society of Powder Technology, Japan 2012年10月 [査読有り]
     
    In a coal-fired thermal power plant, ash particles laden in flue gas adhere on de-NOx catalyst surface, and ash coverage causes the degradation of de-NOx catalyst. Therefore, in this study, effect of the flow in a honeycomb rectangular channel, which represents a single channel of de-NOx catalyst, on the adhesion characteristics of particles to the wall was investigated by applying a direct numerical simulation (DNS). Results show that the adhesion of particles is strongly affected by the flow. The particle adhesion is enhanced by turbulence near the inlet of channel, whereas suppressed due to the attenuation of turbulence in the downstream region. The particle adhesion also depends on particle diameter. Small particles adhere on the wall only in the upstream region, whereas large particles adhere all the way down to outlet, nevertheless flow transients to laminar. This is due to the fact that large particles keep the inertial force even in the downstream region. Moreover, the cross sectional position of particle adhesion also depends on both flow stagnation near the corner and a secondary flow which is driven on the plane normal to the streamwise direction.
  • 道岡 武信; 佐藤 歩
    大気環境学会誌 = Journal of Japan Society for Atmospheric Environment 47 3 119 - 126 大気環境学会 2012年05月 [査読有り]
     
    単純建物周辺および実低層市街地内の気流・拡散場に対してRANSを実行し、風洞実験値との比較によりその適用性を検討した。本数値モデルでは、複雑な建物形状を詳細に解像できるように、座標系に関係なく格子点を不規則に配置できる非構造格子の有限体積法を採用した。また、非構造格子で煙源近傍にも密な計算格子が設定できるため、ガス拡散を気流場と同様にオイラー的に解いた。RANSは比較的大きな建物の後流域において、平均速度および速度変動強度の標準偏差を過小評価する傾向にある。そのため、乱流モデル中に存在するモデルパラメータである乱流シュミット数には比較的小さな値を選択する必要がある。本解析では、乱流シュミット数を 0.2～0.5を適用した場合に、風洞実験値に比較的良い一致を示すが、乱流シュミット数はガス拡散に大きな影響を及ぼし、適切な値を選択しなければ数倍程度の誤差を含む場合がある。
  • Ryoichi Kurose; Naohisa Takagaki; Takenobu Michioka; Naoki Kohno; Satoru Komori
    AICHE JOURNAL 58 2 377 - 384 2012年02月 [査読有り]
     
    The subgrid scale (SGS) variance for a high-Schmidt-number passive scalar of Sc >> 1 is measured using a high-resolution planar laser-induced fluorescence technique in a grid-generated turbulent liquid flow, and the values of the model coefficients in the scale-similarity model and the scalar-gradient model used for estimating the SGS scalar variance are experimentally evaluated. The results show that for both models, the measured values are much larger than the well-known values obtained in the previous studies done for non-high-Sc scalars of Sc congruent to 1. Similarly, the measured value of the model coefficient in the scalar-gradient model tends to be larger than the value estimated by the dynamic procedure. The increases in the measured values of the model coefficients for the high-Sc scalar can be explained by the presence of the viscous-convective range showing a nearly (-1)-slope in the high-wavenumber range of the power spectrum of concentration fluctuation. (C) 2011 American Institute of Chemical Engineers AIChE J, 58: 377-384, 2012
  • 道岡 武信; 佐藤 歩
    土木学会論文集B1（水工学） 68 4 I_1795 - I_1800 Japan Society of Civil Engineers 2012年 [査読有り]
     
    Large-eddy simulation was implemented for airflow and thermal diffusion in an urban canyon. To evaluate the performance of the LES, the mean velocities, standard deviations of turbulent fluctuations and mean temperature estimated by the LES are compared with those obtained by wind-tunnel experiments. The results show that the LES can capture the flow and temperature within the canyon, and accurately represent the effect of the wall heating on flow within the canyon. Though the previous studies only focused on the vertical cross section, it is found that two axisymmetrical vortexes are formed in the horizontal cross section with a large clockwise vortex in vertical cross section irrespective of the wall heating conditions. The horizontal vortexes are enlarged by wall heating, and horizontal turbulent fluctuations are increased. Thus, the thermal environment within the canyon is affected not only by the vertical large vortex, but also by the horizontal turbulent flow.
  • Takenobu Michioka; Ayumu Sato; Koichi Sada
    BOUNDARY-LAYER METEOROLOGY 141 1 35 - 51 2011年10月 [査読有り]
     
    Large-scale turbulent motions enhancing horizontal gas spread in an atmospheric boundary layer are simulated in a wind-tunnel experiment. The large-scale turbulent motions can be generated using an active grid installed at the front of the test section in the wind tunnel, when appropriate parameters for the angular deflection and the rotation speed are chosen. The power spectra of vertical velocity fluctuations are unchanged with and without the active grid because they are strongly affected by the surface. The power spectra of both streamwise and lateral velocity fluctuations with the active grid increase in the low frequency region, and are closer to the empirical relations inferred from field observations. The large-scale turbulent motions do not affect the Reynolds shear stress, but change the balance of the processes involved. The relative contributions of ejections to sweeps are suppressed by large-scale turbulent motions, indicating that the motions behave as sweep events. The lateral gas spread is enhanced by the lateral large-scale turbulent motions generated by the active grid. The large-scale motions, however, do not affect the vertical velocity fluctuations near the surface, resulting in their having a minimal effect on the vertical gas spread. The peak concentration normalized using the root-mean-squared value of concentration fluctuation is remarkably constant over most regions of the plume irrespective of the operation of the active grid.
  • Ryoichi Kurose; Takenobu Michioka; Naoki Kohno; Satoru Komori; Yuya Baba
    AICHE JOURNAL 57 4 911 - 917 2011年04月 [査読有り]
     
    Large-eddy simulations using the flamelet models are applied to turbulent reacting liquid flows and validated by comparing with the experiments. The computations are performed for two reaction conditions, namely a rapid reaction and a moderately fast reaction in a grid-generated turbulent flow. For the flamelet models, both the steady flamelet model and the unsteady Lagrangian flamelet model are tested. A second-order, irreversible, and isothermal reaction is considered. The results show that the flamelet models inherently developed for turbulent combustion are applicable to turbulent reacting liquid flows, provided that the model coefficient in evaluating the subgrid scale variance of mixture fraction in the scale-similarity model is set to be 5.0. The rapid reaction can be adequately predicted by both the steady and unsteady Lagrangian flamelet models, whereas the moderately fast reaction can be predicted only by the unsteady Lagrangian flamelet model which is capable to take slow chemical processes into account. (C) 2010 American Institute of Chemical Engineers AIChE J, 57: 911-917, 2011
  • Takenobu Michioka; Ayumu Sato; Hiroshi Takimoto; Manabu Kanda
    BOUNDARY-LAYER METEOROLOGY 138 2 195 - 213 2011年02月 [査読有り]
     
    Large-eddy simulation (LES) is conducted to investigate the mechanism of pollutant removal from a two-dimensional street canyon with a building-height to street-width (aspect) ratio of 1. A pollutant is released as a ground-level line source at the centre of the canyon floor. The mean velocities, turbulent fluctuations, and mean pollutant concentration estimated by LES are in good agreement with those obtained by wind-tunnel experiments. Pollutant removal from the canyon is mainly determined by turbulent motions, except in the adjacent area to the windward wall. The turbulent motions are composed of small vortices and small-scale coherent structures of low-momentum fluid generated close to the plane of the roof. Although both small vortices and small-scale coherent structures affect pollutant removal, the pollutant is largely emitted from the canyon by ejection of low-momentum fluid when the small-scale coherent structures appear just above the canyon where the pollutant is retained. Large-scale coherent structures also develop above the canyon, but they do not always affect pollutant removal.
  • A. Sato; T. Michioka; H. Takimoto
    INTERNATIONAL JOURNAL OF ENVIRONMENT AND POLLUTION 47 1-4 184 - 192 2011年 [査読有り]
     
    Field experiments of air flow and pollution dispersion within a street canyon in the Comprehensive Outdoor Scale Model (COSMO) facility were conducted to investigate the effect of the mean and turbulent flow above the canyon on pollutant dispersion inside the canyon. Tracer gas concentration was measured using fast-response photo ionisation detectors. Three-dimensional wind velocity components were also simultaneously measured using ultrasonic anemometers within and above the same canyon. Using both tracer gas concentration and velocity fluctuation data, we investigated the effects of atmospheric turbulence above the height of the buildings on pollution dispersion within the street canyon.
  • 道岡 武信; 佐藤 歩; 服部 康男
    日本機械学會論文集. B編 76 765 823 - 829 一般社団法人日本機械学会 2010年 [査読有り]
     
    A wind tunnel experiment was conducted to simulate large-scale turbulent motions in an atmospheric boundary layer (ABL). The large-scale turbulent motions originating from outer-layer disturbance were generated using an active grid installed at the front of the test section and the winglets of the active grid were randomly rotated. The large-scale horizontal motions in the ABL were generated in the wind tunnel using the active grid when appropriate values of the angle and rotation speed were chosen. The validity of the present method using the active grid was confirmed by comparing the integral scale and energy spectra obtained by the experiments with empirical formulas inferred from field observations. This indicates that the present method of using the active grid accurately simulates the turbulent motions in a nearly neutral ABL.
  • 道岡 武信; 佐藤 歩; 佐田 幸一
    日本機械学會論文集. B編 75 749 93 - 100 一般社団法人日本機械学会 2009年01月 [査読有り]
     
    We developed a method for a wind tunnel experiment to predict a visible plume region from a mechanical-draft cooling tower. The diffusions of water vapor and temperature emitted from the cooling tower in the wind tunnel experiment are tracked using tracer gas. It is assumed that the plume-induced fog is generated whenever the instantaneous specific humidity predicted from the concentration of the tracer gas at measuring points is larger than the inferred saturation specific humidity. To estimate the accuracy of the present method, the measurements are compared with the observations. The results show that the visible plume length and height are in good agreement with the observations. Furthermore, it is found that the visible length and height is strongly affected by wind direction to the cooling tower, temperature difference between atmosphere and exit of the cooling tower and atmospheric humidity, and hence the present wind tunnel method considered these conditions is valid to predict the visible plume.
  • 河野 直紀; 黒瀬 良一; 小森 悟; 道岡 武信; 馬場 雄也
    化学工学会 研究発表講演要旨集 2009 118 - 118 公益社団法人 化学工学会 2009年
  • 佐田 幸一; 込山 有人; 道岡 武信; 市川 陽一
    日本原子力学会和文論文誌 = Transactions of the Atomic Energy Society of Japan 8 2 184 - 196 Atomic Energy Society of Japan 2009年 [査読有り]
     
    A numerical simulation method has been developed to predict atmospheric flow and stack gas diffusion, considering the buildings and complex terrain located near and relatively far from a stack, respectively. The turbulence closure technique was used for flow calculation, some calculation grids on the ground near a stack were treated as buildings, and stack gas diffusion was predicted using the Lagrangian particle model. The calculated flow and stack gas diffusion results were compared with those obtained by wind tunnel experiments under actual terrain containing buildings. Effective stack height was estimated by comparing the surface concentration along the plume axis with those under a flat-plate condition, and it was apparent that the effective stack heights estimated by calculations were almost the same as those obtained by the wind tunnel experiment. Then, the effective dose and relative concentration of stack gas were calculated using the effective stack heights obtained by a numerical model. Almost the same effective dose and relative concentration were obtained when compared with those using the effective stack height obtained by wind tunnel experiment.
  • 道岡 武信; 佐藤 歩; 佐田 幸一
    日本機械学會論文集. B編 75 752 604 - 611 一般社団法人日本機械学会 2009年 [査読有り]
     
    A Large-eddy simulation (LES) was developed to predict a visible plume region from a mechanical-draft cooling tower. This numerical model solves the equations for conservation of mass, momentum, energy, vapor and liquid water. It is assumed that the visible plume is generated whenever the instantaneous liquid water mixing ratio is existed. To estimate the accuracy of the present numerical model, the predictions of visible plume length and height are compared with observations. The results show the visible plume length and height are in good agreement with the observations. Furthermore, we investigate the basic behavior of the visible plume and temperature emitted from the cooling tower under severe metrological condition. It is found that whether the visible plume reaches the ground or not mostly depends on the wind angle to the cooling tower, and temperature emitted from the cooling tower has little influence on atmosphere environment on the ground.
  • 下田 昭郎; 道岡 武信; 佐田 幸一; 佐藤 歩; 神崎 隆男; 和田 浩治; 市川 陽一
    大気環境学会誌 44 5 255 - 261 Japan Society for Atmospheric Environment 2009年 [査読有り]
     
    近年，我が国に設置されることの多い白煙化対策機能の付いた機械通風式の発電所冷却塔の白煙予測，飛散液滴予測，および温度・湿度影響が予測可能なモデル開発にあたり，既存モデルおよび開発モデルの適用性検証に必要な情報収集を目的として，実際の冷却塔を対象とした実態調査を実施した。調査の結果，白煙による地上温度・湿度への影響は確認できなかった。白煙の高さおよび長さに関しては，夜間の測定も可能なサーモグラフィを用いることにより，観測期間中で100ケース以上の白煙についてデータ収集ができた。冷却塔からの飛散液滴については，調査対象冷却塔が飛散防止のためのエリミネータを装備したものであったため，地上への沈着は極めて少ないものであった。
  • 道岡 武信; 佐藤 歩; 下田 昭郎; 佐田 幸一; 市川 陽一; 大蔵 革
    大気環境学会誌 44 5 227 - 235 Japan Society for Atmospheric Environment 2009年 [査読有り]
     
    我が国の機械通風式冷却塔からの白煙，湿度，温度および液滴飛散量を予測するための解析解モデルを開発した。本モデルは冷却塔ファン位置，大気安定度，大気の気温減率を考慮でき，さらに湿式・乾式併用冷却塔にも適用可能である。既存モデル(FOGモデル，SACTIモデル)および本モデルの精度を検討するために，我が国の機械通風式冷却塔での実態観測から得られた白煙長さ・高さ，地表面温度・湿度，液滴飛散量を比較検討した。その結果，FOGモデルおよびSACTIモデルでは冷却塔からの白煙を精度良く予測できないこと，また，SACTIモデルでは液滴沈着量を過小評価する傾向があることがわかった。一方，本モデルから予測した白煙長さ・高さ，地表面温度・湿度，液滴飛散量は実態観測値に良く一致しており，各種統計値から判断しても既存モデルより精度良く白煙予測可能であることが明らかとなった。
  • 道岡 武信; 佐藤 歩; 佐田 幸一; 下田 昭郎; 市川 陽一
    大気環境学会誌 44 3 147 - 154 Japan Society for Atmospheric Environment 2009年 [査読有り]
     
    機械通風式冷却塔の建屋形状や複数ファンの配列がプルーム上昇および拡散幅に及ぼす影響を風洞実験により検討した。単一のファンを想定した拡散実験により，冷却塔の建屋長さ・高さがプルーム上昇，水平方向および鉛直方向拡散幅に及ぼす影響は非常に小さいことが明らかになった。また，複数ファンを有する冷却塔の拡散実験より，プルーム上昇高さは，冷却塔ファン数および風向に強く依存することがわかった。風向が冷却塔の長手方向に平行の場合，ファン数が増加するほどプルーム上昇高さは大きくなるが，風向が垂直の場合，ファン数とともにプルーム上昇高さはあまり大きくならない。また，鉛直および水平方向拡散幅はプルーム上昇高さとは異なり，ファンの配列よりも冷却塔ファンの個数に強く依存する。<BR>風洞実験結果を基に機械通風式冷却塔白煙に適用可能なプルーム上昇モデルおよび拡散幅モデルの開発を行った。また，既存モデル(FOGモデル)および開発モデル式の精度を検討するために，風洞実験値と比較した。その結果，既存モデルはファン配置や個数を考慮することができず，上記現象を再現できない。それに対して，ファン配置や個数を考慮できる本開発モデルは，プルーム上昇高さおよび拡散幅の風洞実験値を良好に再現することができた。
  • Takenobu Michioka; Fotini Katopodes Chow
    Journal of Applied Meteorology and Climatology 47 12 3150 - 3169 2008年12月 [査読有り]
     
    This paper presents high-resolution numerical simulations of the atmospheric flow and concentration fields accompanying scalar transport and diffusion from a point source in complex terrain. Scalar dispersion is affected not only by mean flow, but also by turbulent fluxes that affect scalar mixing, meaning that predictions of scalar transport require greater attention to the choice of numerical simulation parameters than is typically needed for mean wind field predictions. Large-eddy simulation is used in a mesoscale setting, providing modeling advantages through the use of robust turbulence models combined with the influence of synoptic flow forcing and heterogeneous land surface forcing. An Eulerian model for scalar transport and diffusion is implemented in the Advanced Regional Prediction System mesoscale code to compare scalar concentrations with data collected during field experiments conducted at Mount Tsukuba, Japan, in 1989. The simulations use horizontal grid resolution as fine as 25 m with up to eight grid nesting levels to incorporate time-dependent meteorological forcing. The results show that simulated ground concentration values contain significant errors relative to measured values because the mesoscale wind typically contains a wind direction bias of a few dozen degrees. Comparisons of simulation results with observations of arc maximum concentrations, however, lie within acceptable error bounds. In addition, this paper investigates the effects on scalar dispersion of computational mixing and lateral boundary conditions, which have received little attention in the literature-in particular, for high-resolution applications. The choice of lateral boundary condition update interval is found not to affect time-averaged quantities but to affect the scalar transport strongly. More frequent updates improve the simulated ground concentration values. In addition, results show that the computational mixing coefficient must be set to as small a value as possible to improve scalar dispersion predictions. The predicted concentration fields are compared as the horizontal grid resolution is increased from 190 m to as fine as 25 m. The difference observed in the results at these levels of grid refinement is found to be small relative to the effects of computational mixing and lateral boundary updates.
  • MICHIOKA Takenobu; KUROSE Ryoichi
    Journal of Fluid Science and Technology 3 5 610 - 621 The Japan Society of Mechanical Engineers 2008年 
    Large-eddy simulations (LES) are applied to particle-laden swirling jets, and effect of the swirl on particle dispersion is investigated. The trajectories of all particles are individually pursued with a Lagrangian method. The particles with different diameters are uniformly injected into a non-swirling flow or swirling flows with different swirling numbers. The results show that the trajectories of the particles largely differ depending on their diameters. In swirling jets, the peak of particle number density for small particle is located on the central axis, whereas that for larger particles is shifted outward by the centrifugal force. However, the larger particles, which migrate outward in the upstream region, tend to gradually migrate inward toward downstream, and this trend is remarkable as the particle diameter decreases. This is due to the fact that the direction of the particle migration in the downstream region is dominated by the turbulent motions, which act to transport the smaller particles inward in wide range of the swirling jets.
  • Koichi Sada; Takenobu Michioka; Yoichi Ichikawa
    Asian Journal of Atmospheric Environment 2 1 1 - 13 2008年 [査読有り]
     
    A numerical simulation method has been developed to predict atmospheric flow and stack gas diffusion using a calculation domain of several km around a stack under complex terrain conditions containing buildings. The turbulence closure technique using a modified k-ε-type model under a nonhydrostatic assumption was used for the flow calculation, and some of the calculation grids near the ground were treated as buildings using a terrain-following coordinate system. Stack gas diffusion was predicted using the Lagrangian particle model, that is, the stack gas was represented by the trajectories of released particles. The numerical model was applied separately to the flow and stack gas diffusion around a cubical building and to a two-dimensional ridge in this study, before being applied to an actual terrain containing buildings in our next study. The calculated flow and stack gas diffusion results were compared with those obtained by wind tunnel experiments, and the features of flow and stack gas diffusion, such as the increase in turbulent kinetic energy and the plume spreads of the stack gas behind the building and ridge, were reproduced by both calculations and wind tunnel experiments. Furthermore, the calculated profiles of the mean velocity, turbulent kinetic energy and concentration of the stack gas around the cubical building and the ridge showed good agreement with those of wind tunnel experiments.
  • 佐藤 歩; 瀧本 浩史; 道岡 武信
    風工学シンポジウム論文集 20 0 21 - 21 Japan Association for Wind Engineering 2008年 [査読有り]
     
    都市の建物周辺の流れ場は大気の温度成層状態に影響を受けるため、都市内での汚染物質の拡散を予測するためには温度成層の影響を考慮することが重要である。本研究では、不安定成層が建物後流に与える影響を検討するため、温度成層風洞内に３種類の不安定成層流を模擬し、立方体建物後流における流れ場をLDV及びPIVにより計測し、以下の知見を得た。不安定時の建物背後では、中立時と同様に平均風速が負の値を示す逆流域が形成され、逆流風速の大きさや風下方向への広がりは中立時と類似の分布を示す。特に、建物背面近傍では熱浮力による乱れの生成に比べ建物による乱れの生成が卓越するため変動風速の標準偏差やレイノルズ応力は中立時とほぼ等しい値を示す。一方、強い不安定時には建物屋根面より放出される剥離渦が熱浮力により大きく乱され、また逆流域の温度上昇により上空気流の巻き込みが抑制されるため、建物背後の循環渦は形成されにくくなる。
  • Takenobu Michloka; Ayumu Sato; Takao Kanzaki; Kouichl Sada
    JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS 95 8 741 - 754 2007年08月 [査読有り]
     
    We developed a new method for a wind tunnel experiment to predict a visible plume region from a wet cooling tower. The diffusion of water vapor and beat emitted from a cooling tower in a wind tunnel is estimated using a tracer gas. The instantaneous concentration of the tracer gas is measured using high-response flame ionization detectors. A moist plume-induced fog is assumed to be generated whenever the instantaneous specific humidity predicted from the concentration of the tracer gas at measured points is larger than the inferred saturation specific humidity. To confirm the validity of the present method, the results in the wind tunnel experiments are roughly compared with the observations obtained at the mechanical-draft cooling tower of the Benning Road plant. The results show that the visible plume length and height are nearly in agreement with observations and the present method has the capability to predict the visible plume region from the cooling tower. (c) 2007 Elsevier Ltd. All rights reserved.
  • 道岡 武信; 黒瀬 良一
    日本機械学会論文集 B編 73 725 30 - 37 The Japan Society of Mechanical Engineers 2007年 [査読有り]
     
    Three-dimensional large-eddy simulation (LES) is applied to a particle-laden swirling jet, and the effect of swirl on particle diffusion is investigated. The trajectories of all particles are individually pursued with a Lagrangian method. The particles with different diameters are uniformly injected into the non-swirling and swirling flows with different Swirling numbers. The result shows that the trajectories of the particles with different diameters are quite different. The smaller particles have the peak of the particle number densities at central axis, and diffuse across swirling jet. On the other hand, the larger particles at the exit of the nozzle migrate outward by the centrifugal force, but the particles gradually migrate inward with the axial distance increases. The inward movement of the particle in the downstream region is dominated by turbulent motions, which transport the particles inward near central axis. Furthermore, above behavior is shifted upstream with the particle diameter decrease because the smaller particles are easily transferred by smaller inward fluid motions existing in the wide range of the swirling jet.
  • 黒瀬 良一; 道岡 武信; 牧野 尚夫; 小森 悟
    粉体工学会誌 44 2 107 - 112 The Society of Powder Technology, Japan 2007年 [査読有り]
     
    Effect of flow behavior in a honeycomb rectangular channel of a de-NOX catalyst on the adhesion of particles onto the wall is studied using a direct numerical simulation (DNS). The results show that the adhesion of particles is markedly affected by the turbulent-laminar-transition flow and is enhanced by the turbulence in the upstream region near the inlet. This agrees well with the previous experimental observation, in which the degradation of catalyst appeared in the region near the inlet. The adhesion of particles is found to be enhanced by the turbulence especially for larger particles. In the downstream region, the adhesion on the wall near the corners of rectangular channels is suppressed since the turbulent-laminar transition proceeds from these regions.
  • Koichi Sada; Takenobu Michioka; Yoichi Ichikawa
    JSME International Journal, Series B: Fluids and Thermal Engineering 49 1 48 - 59 2006年08月 
    A numerical simulation method has been developed to predict atmospheric flow and stack gas diffusion under a neutral stratification condition, considering the buildings and complex terrain located near and relatively far from a stack, respectively. The turbulence closure technique was used for flow calculation, some calculation grids on the ground within a plant area were treated as buildings, and stack gas diffusion was predicted using the Lagrangian particle model. The calculated flow and stack gas diffusion results were compared with those obtained by wind tunnel experiments under a neutral stratification condition, and the features of surface concentration, such as the occurrence of downdraft phenomena behind the buildings, were reproduced by both calculations and wind tunnel experiments. Furthermore, effective stack heights were estimated by the comparison of the surface concentration along the plume axis with those under a flat-plate condition, and it was apparent that the effective stack heights estimated by calculations were almost the same as those obtained by wind tunnel experiments. Copyright © 2006 by The Japan Society of Mechanical Engineers.
  • T Michioka; R Kurose; K Sada; H Makino
    INTERNATIONAL JOURNAL OF MULTIPHASE FLOW 31 7 843 - 866 2005年07月 [査読有り]
     
    A direct numerical simulation (DNS) is applied to a particle-laden turbulent mixing layer with a chemical reaction, and the effects of particles on turbulence and chemical species' diffusion and reaction in both zero and finite gravity cases are investigated. Unreactive particles, whose response time, tau(P), is smaller than the Kolmogorov time scale, tau(K) [tau(P)/tau(K) = O(10(-1))], are uniformly injected into the high-speed side of the mixing layer. Two reactive chemical species are separately introduced through different sides. The results show that although laden particles generally depress turbulent intensities, they begin to enhance turbulent intensities downstream as the particle size decreases provided that the inlet particle volume fraction is fixed. This is because that the small particles with small particle response time easily accumulate at the circumference of coherent vortices and act to suppress the growth of primitive small-scale coherent vortices upstream but enhance that of relatively developing large-scale ones downstream. Also, since the small-scale turbulence, which promotes the chemical reaction, is suppressed by the laden particles in the entire region, chemical product decreases overall. Furthermore, the presence of finite gravity on the particles acts to depress the turbulent intensities, but its effects on chemical species' diffusion and reaction are quite small. (c) 2005 Elsevier Ltd. All rights reserved.
  • T Michioka; S Komori
    AICHE JOURNAL 50 11 2705 - 2720 2004年11月 [査読有り]
     
    A subgrid-scale (SGS) model for the filtered reaction source term is presented to develop the large-eddy simulation (LES) of a nonpremixed, turbulent liquidflow with a moderately fast reaction. The SGS model is based on the SGS probability density function (PDF) and SGS conditional expectation. The SGS probability density function (SGS-PDF) is assumed to follow a beta distribution and a simple algebraic model for the SGS conditional expectation is developed using the filtered data obtained from the direct numerical simulation (DNS) of stationary isotropic liquid turbulence with a second-order chemical reaction. For a rapid reaction, the SGS-PDF model based on the conserved scalar is used as the SGS model. The LES based on these SGS models is applied to a liquid mixing layer flow downstream of a turbulence-generating grid with a chemical reaction, and the LES predictions of the mean concentration and concentration variance are directly compared with the previous measurements for both moderately fast and rapid reactions to examine the proposed SGS models. The results show that the predictions by the LES are in good agreement with the measurements and the present LES can well describe the diffusive-reactive process in a turbulent reacting liquidflow. (C) 2004 American Institute of Chemical Engineers.
  • 大西 領; 道岡 武信; 長田 孝二; 小森 悟
    日本機械学会論文集Ｂ編 69 679 636 - 643 一般社団法人 日本機械学会 2003年 [査読有り]
     
    The effects of thermal stratifications on turbulent mixing and chemical reaction in the liquid mixing layer were investigated by both laboratory experiments and numerical simulations. The experiments were conducted in neutrally, unstably and stably stratified water flows with a rapid chemical reaction. Instantaneous velocities and concentration were simultaneously measured using a combined technique with a two component laser-Doppler velocimeter (LDV) and a later-induced fluorescence (LIF) method. Turbulence quantities such as the mean concentration of chemical product and turbulent mass fluxes were estimated and the effects of thermal stratifications on the quantities were clarified. Further, the large-eddy simulation (LES) using the large-eddy probabil- ity-density function (LEPDF) model as a SGS model was applied to the thermally-stratified reacting liquid flows. The results show that the effects of the stratifications on the turbulent mixing and chemical reaction can be well explained by the LES.
  • R Kurose; H Makino; T Michioka; S Komori
    COMBUSTION AND FLAME 127 3 2157 - 2163 2001年11月 [査読有り]
  • 道岡武信; 長田孝二; 井田敦巳; 小森悟
    日本機械学会論文集(B編) 66 651 2815 - 2822 2000年 [査読有り]
     
    A large eddy simulation (LES) based on a finite volume method was applied to a liquid mixing layer flow downstream of a turbulence-generating grid with chemical reactions. The large eddy probability density function (LEPDF) model and joint LEPDF model were used as a SGS model for a rapid reaction and for a moderately fast reaction, respectively. The results of the LES were compared with the measurements to examine the proposed subgrid-scale (SGS) models. Furthermore, the correlation coefficient in the scale similarity model between the variance of SGS concentration and that of test-filtered concentration was determined using the data of the direct numerical simulation (DNS) of liquid isotropic turbulence. The results show that the correlation coefficient for a liquid flow is 5 times bigger than that for a gas flow. When the appropriate correlation coefficent is given, the LES results are in good agreement with the measurements.
  • 道岡武信; 小森悟
    日本機械学会論文集(B編) 65 32 839 - 846 1999年 [査読有り]

MISC

受賞

  • 2018年04月 日本原子力学会 関東・甲越支部 技術貢献賞
     安全解析のための原子力発電所排ガス拡散予測の数値モデルの開発 
    受賞者: 佐田幸一;道岡武信
  • 2012年 粉体工学会 技術賞
     数値シミュレーションによるハニカム形脱硝触媒の劣化特性評価 
    受賞者: 丹野賢二;道岡武信;牧野尚夫;黒瀬良一;小森悟
  • 2010年 日本原子力学会 保健物理・環境科学部会 論文賞
     安全解析のための数値モデルによる排ガス大気拡散予測および被ばく線量評価－風洞実験と数値モデルによる放出源の有効高さ・被ばく線量－ 
    受賞者: 佐田幸一;込山有人;道岡武信;市川陽一
  • 2010年 大気環境学会 論文賞（原著論文）
     機械通風式冷却塔からの白煙予測手法（その１）―プルーム上昇・拡散モデルの開発― 
    受賞者: 道岡武信;佐藤歩;佐田幸一;下田昭朗;市川陽一
  • 2005年 日本機械学会 日本機械学会
     化学反応を伴う乱流場に対するLarge-Eddy Simulationの開発 
    受賞者: 道岡武信

共同研究・競争的資金等の研究課題

  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2022年04月 -2025年03月 
    代表者 : 道岡 武信
  • 日本学術振興会：科学研究費助成事業 基盤研究(C)
    研究期間 : 2018年04月 -2022年03月 
    代表者 : 道岡 武信
     
    都市街区内には乱流の理論では説明することができない低周波数の周期を有する流れ（風の揺らぎ）が存在することが次第に明らかになってきた。この風の揺らぎは都市内の汚染物質拡散に大きな影響を与える可能性がある乱流現象であるものの、その発生メカニズムおよび構造はほとんど分かっていない。本研究題目では、都市街区を対象に、詳細数値シミュレーションにより風の揺らぎの構造およびその発生メカニズムを解明することを目的とする。平成30年度の実施概要は以下の通りである。 理想的な都市街区を対象に詳細数値シミュレーション（ラージ・エディ・シミュレーション）を実施した結果、低周波数乱流変動（風の揺らぎ）が発生することがわかった。また、その低周波数乱流変動は、2列目の地表面近傍で形成され、風下に行くに従い低周波数乱流変動は発達し、7列目以降では一定の低周波数で運動することが明らかになった。しかしながら、なぜ2列目で生成されるのか、また、なぜ一定の周期で運動するのかは分かっておらず、今後詳細な検討が必要である。 風が一方向から吹く定常の条件下では，理想的な都市街区内の低周波数乱流変動が発生することが明らかになったが，実際の大気中には風向変動などの大きな変動が存在しており，風向変動が存在する流れ場において低周波数乱流変動の存在は明らにされていない．そこで，風向変動が街区内の乱流，特に低周波数乱流変動に及ぼす影響をラージ・エディ・シミュレーションにより検討した。その結果，風向変動を考慮した場合でも，街区内に低周波数乱流変動が生成されることが明らかになった。ただし，風向変動はその運動の周期に影響を与えるため、今後詳細を解明する必要がある。
  • 文部科学省：科学研究費補助金(基盤研究(C))
    研究期間 : 2015年04月 -2018年03月 
    代表者 : 道岡 武信
     
    我が国の環境影響評価では１時間以上平均化された濃度値が使用されている。都市キャニオンにおいてその濃度値を正確に評価するためには風洞変動など大きな風の変動を考慮した数値シミュレーションでガス拡散を評価する必要がある可能性がある。しかしながら、風向変動の有無がガス拡散に及ぼす影響は明らかにされていない。本研究では理想的な街区を対象に風向変動を考慮した数値シミュレーションを実行し、風向変動がガス拡散に及ぼす影響を検討した。その結果、本解析で対象とした理想的な街区では、1時間程度の風向変動は都市キャニオン内のガス拡散に及ぼす影響は小さいことがわかった。
  • 文部科学省：科学研究費補助金(若手研究(B))
    研究期間 : 2013年04月 -2015年03月 
    代表者 : 道岡 武信
     
    都市内での大気質の改善策や、防災などに関連した都市内のガス拡散においては、接地境界層内のシアーなどの機械的に生成される乱流渦がガス拡散を支配すると言われてきた。しかしながら、実際の都市キャニオンでは接地層外の大規模な乱流やキャニオン外の乱流も都市内のガス拡散に大きな影響を与える可能性がある。そこで、キャニオン内で生成される乱流だけではなく、接地境界層外の大規模な乱流構造やキャニオン外の乱れが都市内のガス拡散に及ぼす影響を検討する。平成25年度は、立方体建物が規則的に配列された理想的な都市キャニオンにおいて、キャニオン内からのガスの排出メカニズムに関して検討した。その結果、我々のグループが理想的な２次元のストリートキャニオンにおける研究から明らかにしてきたように、キャニオン上空に存在する組織的な乱流構造が、３次元の都市キャニオン内からのガス放出にも寄与することが明らかになった。ただし、十分に発達した乱流場においては接地境界層外の大規模な乱流構造が理想的な都市内のガス拡散に明確に影響を及ぼすことを確認できなかった。次に、都市キャニオンで生成される接地境界層内の乱流ではなく、キャニオン外の流れ場がキャニオン内のガス拡散に及ぼす影響を検討するために、最も風上側の建物からの距離(フェッチ)が都市内のガス拡散に及ぼす影響を検討した。その結果、風上側から3列目程度のキャニオンでは、上空の組織的な乱流構造がガス拡散に影響を及ぼしているのではなく、建物近傍で生成された乱れがガス拡散に寄与していることがわかった。
  • 文部科学省：科学研究費補助金(若手研究(B))
    研究期間 : 2011年04月 -2013年03月 
    代表者 : 道岡 武信
     
    大気安定度が中立、安定、不安定の条件下において、都市キャニオンからのガス放出メカニズムをラージ・エディ・シミュレーションにより検討した。その結果、都市キャニオン上空で発達する組織的な低速流体塊の大きさとガス放出には非常に強い相関があることがわかった。また、大気安定度にかかわらず、その低速流体塊が持ち上げられるイジェクションと呼ばれる乱流運動により、キャニオン内のガスは上空に放出されることを明らかにした。

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