著者

辻村 真治 飯田 雄章 長野 靖尚

出版者

一般社団法人 日本機械学会

雑誌

日本機械学会論文集B編 (ISSN:03875016)

巻号頁・発行日

vol.67, no.659, pp.1762-1769, 2001

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In the Earth's atmosphere, zonal currents with a vertical velocity gradient are induced under the action of rotation and horizontal temperature gradient. These currents satisfying the so-called "thermal wind equation" generate the cyclones and anticyclones through the baroclinic instability, and hence have serious effects on the global circulation. In this study, the generation and development mechanisms of vertical vortices associated with the cyclones and anticyclones are investigated by using direct numerical simulation of the thermal wind. By imposing the stable density stratification in the vertical direction, the effects of the stable stratification and the Reynolds number are studied in detail. As a result, we have found the distinct effects of stable stratification on the anisotropy of the flow field and the generation of the vortical structure. It is also found that the cyclone becomes dominant in comparison to the anticyclone at a relatively low Reynolds number under the weak stable stratification. At a higher Reynolds number, both cyclonic and anticyclonic vortices are enhanced by the nonlinear vortex stretching term, and hence the asymmetry between them becomes negligible. The intensive stable stratification attenuates the nonlinear vortex stretching and contributes to the occurrence of the asymmetry in the vortices even at the higher Reynolds numbers

著者

福留 功二 飯田 雄章 長野 靖尚

出版者

社団法人 日本伝熱学会

雑誌

日本伝熱シンポジウム講演論文集 第45回日本伝熱シンポジウム

巻号頁・発行日

pp.143, 2008 (Released:2008-05-14)

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ポアズイユ乱流において,レイノルズ数を減少させていくと,乱流構造が間欠的になり,摩擦の大きい乱流領域と小さい擬層流領域が現れる.この構造は熱や運動量の輸送に大きな影響を与える.しかし,その発生メカニズムや維持機構など未知な部分が多い.本研究では,ポアズイユ乱流のレイノルズ数を100から60まで段階的に低下させた.この場合に発生する間欠構造を乱流領域と擬層流領域に分割し,それぞれの領域で縦渦やストリークなどの準秩序構造について議論する.

著者

安倍 賢一 長野 靖尚 近藤 継男

出版者

一般社団法人日本機械学会

雑誌

日本機械学會論文集. B編 (ISSN:03875016)

巻号頁・発行日

vol.60, no.573, pp.1743-1750, 1994-05-25

被引用文献数

3

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We propose a new two-equation heat-transfer model which is modified from the model developed by Nagano, Tagawa and Tsuji (Proc. ASME/JSME Thermal Eng. Joint Conf., 3 (1991), 233). The main improvement is made by introducing the Kolmogorov velocity scale, u_ε≡(νε)^<1/4>, instead of the friction velocity u_τ, to account for the wall-limiting behavior. After investigating the characteristics of various time scales for the heat-transfer model, we employed a composite time scale which gives weight to a shorter scale among the velocity- and temperature-field time scales. With these modifications, it is shown that the present model quite successfully predicts the turbulent heat transfer in a boundary layer subjected to sudden change of heat flux, and in a separating and reattaching flow downstream of a backward-facing step.

著者

長野 靖尚 服部 博文 宮澤 純 稲垣 賢一郎

出版者

一般社団法人日本機械学会

雑誌

日本機械学會論文集. B編 (ISSN:03875016)

巻号頁・発行日

vol.70, no.696, pp.1911-1918, 2004-08-25

被引用文献数

1

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It is well known that the turbulence energy is overpredicted by the k-ε model at the stagnation point. This problem causes inadequate predictions of flow field. In particular, since the wind-power energy is proportional to wind velocity cubed, it is crucial to predict a correct profile of wind in selecting the best site for a wind-power plant. The effects of the ground are often neglected owing to the very large length scale of the real environment. However, the complex terrain affects a profile of wind near the ground. Therefore, we have to consider the ground effects to obtain an exact profile of wind near the ground. In this study, to evaluate the performance of a low-Reynolds-number type turbulence model for flows on a complex terrain, we carried out a simulation of a flow around various complex terrain. From evaluation, we have improved the model introducing the time scale based on the velocity gradient parameter. The proposed model is evaluated in four complex turbulent flows, i.e., forward-facing step, two-dimensional block, two-dimensional hill and three-dimensional block flows. The proposed model indicates good agreement with the experimental data.