Papers - Obi, Shinnosuke

Passive control of flow around a circular cylinder using porous media

NAITO HIROSHI, FUKAGATA KOJI, OBI SHINNOSUKE

7th JSME-KSME Thermal and Fluids Engineering Conference  2008.10

Research paper (conference, symposium, etc.), Joint Work, Accepted

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Passive flow control around circular cylinder using porous media is studied by means of two-dimensional numerical simulation. Brinkman-Navier-Stokes equation is used to simulate flow in the porous media. The simulation is performed at the Reynolds number of Re = 100 and 1000. Both the drag and lift forces are found to be modified due to the presence of porous media. Especially, the fluctuation of lift force is suppressed at Re = 1000 with an intermediate value of porosity. The case of minimum lift force fluctuation is investigated in detail by examining the statistics and flow visualization.

Velocity-pressure correlation measurements in complex free shear flows

NAKA YOSHITSUGU, OBI SHINNOSUKE

7th Int. Symp. Engineering Turbulence Modelling and Measurements (European Research Collaboration on Flow Turbulence and Combustion)     375-380 2008.06

Research paper (conference, symposium, etc.), Single Work, Accepted

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乱流せん断層において変動圧力速度相関を計測する新しい手法を開発しその性能評価を行なった。従来のミニチュアピトー管ではマルチセンサー型熱線風速計との併用において空間解像度に制限があったが、新しくミニチュア全圧プローブを併用する手法を開発し、基本性能の評価と旋回乱流への適用を通じて妥当性を示した。

A modification of the elliptic relaxation equation to account for pressure transport in RANS modelling

HUI JING and OBI SHINNOSUKE

7th Int. Symp. Engineering Turbulence Modelling and Measurements (European Research Collaboration on Flow Turbulence and Combustion)     95-100 2008.06

Research paper (conference, symposium, etc.), Joint Work, Accepted

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レイノルズ応力の圧力拡散モデルについて、楕円型緩和方程式を用いたモデルの援用を提唱し、乱流クウェット流れへの適用を通じてその妥当性を示した。また、DNSデータによるアプリオリテストを行い、従来言われていた斉次モデルの選択方法に対して壁面近傍の漸近挙動を満たすモデルを採用しなければならないことを指摘した。

Shearless and sheared flow past a circular cylinder: comparative analysis by means of LES

OMORI TAKESHI, JAKIRLIC SUAD, TROPEA CAMERON and OBI SHINNOSUKE

International Journal of Heat and Fluid Flow 29   703-720 2008.06

Research paper (scientific journal), Joint Work

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固気昆相流中の球形粒子の振る舞いを解明する目的でLESによる数値シミュレーションを行なった。主流の速度分布が一様な場合とせん断がある場合について、円柱に作用する抗力に発生する変化を詳細に調べ、レイノルズ応力の発生機構との関連で論じた。

Evaluation of extended weak-equilibrium condition for fully developed rotating channel flow

QIU JIFENG, GATSKI TOMAS, and OBI SHINNOSUKE

Flow, Turbulence and Combustion 80 ( 4 ) 435-454 2008.06

Research paper (scientific journal), Joint Work, Accepted

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The weak-equilibrium condition, which is the basis in the development of algebraic Reynolds stress models is assessed in the prediction of fully developed
turbulent channel flow under the influence of system rotation. The budget of the various terms of the exact transport equation for the anisotropy tensor is evaluated
by using a DNS database. Two diffusive transport constraints are evaluated by using the DNS data. The results show that neither of them can hold for the nearwall
region. An asymptotic analysis of the near-wall behavior is performed and an alternative form of the diffusive transport constraint is proposed. The analysis shows that the proposed alternative diffusive transport constraint has the potential to improve the predictive ability of the resultant ARSM.

Evaluation of extended weak-equilibrium conditions for fully developed rotating channel flow

Qiu J.F., Obi S., Gatski T.B.

Flow, Turbulence and Combustion (Flow, Turbulence and Combustion)  80 ( 4 ) 435 - 454 2008.06

ISSN  13866184

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The weak-equilibrium condition, which is the basis in the development of algebraic Reynolds stress models is assessed in the prediction of fully developed turbulent channel flow under the influence of system rotation. The budget of the various terms of the exact transport equation for the anisotropy tensor is evaluated by using a DNS database. Two diffusive transport constraints are evaluated by using the DNS data. The results show that neither of them can hold for the near-wall region. An asymptotic analysis of the near-wall behavior is performed and an alternative form of the diffusive transport constraint is proposed. The analysis shows that the proposed alternative diffusive transport constraint has the potential to improve the predictive ability of the resultant ARSM. © 2008 Springer Science+Business Media B.V.

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The study of colliding vortex rings using a special-purpose computer and FMM

SHEEL TARUN KUMAR, YOKOTA RIO, YASUOKA KENJI, and OBI SHINNOSUKE

Transactions of the Japan Society for Computational Engineering and Science 2008   20080003 2008.02

Research paper (scientific journal), Joint Work, Accepted

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分子動力学専用計算機MDGRAPE3を渦法による流体の数値シミュレーションに応用し、FMMとの組み合わせにより計算速度の加速を試みた。汎用計算機の場合と異なり、FMMにおける最適化に際して直接計算の比重を考慮した結果、100倍以上の加速性能を得ることができた。

翼端渦流れにおける速度・圧力相関の測定 (境界層・せん断流・遷移 (3), 一般講演)

中吉嗣， 河田卓也， 深潟康二， 小尾晋之介

日本流体力学会年会講演論文集 2008, 48  2008

多孔質体の表面を持つ円柱周りの流れの数値シミュレーション (流れの制御 (4), 一般講演)

内藤弘士， 深潟康二， 小尾晋之介

日本流体力学会年会講演論文集 2008, 347  2008

専用計算機と FMM を用いた衝突渦輪の渦法解析

シール・タルン・クマー， 横田理央， 泰岡顕治， 小尾晋之介

日本計算工学会論文集 2008, 20080003-20080003  2008

平行平板間流れにおける進行波状体積力による摩擦抵抗低減効果の線形解析 (流れの制御 (2), 一般講演)

守裕也， 深潟康二， オプフナージェローム， 小尾晋之介

日本流体力学会年会講演論文集 2008, 330  2008

渦法を用いた平行平板間乱流の解析 (乱流の予測とモデリング (1), 一般講演)

横田理央， 深潟康二， 小尾晋之介

日本流体力学会年会講演論文集 2008, 337  2008

周期撹乱を用いた二次元混合層の混合制御の数値シミュレーション (流れの制御 (2), 一般講演)

島田幸輔， 深潟康二， 小尾晋之介

日本流体力学会年会講演論文集 2008, 331  2008

639 タービンブレードにおけるラビリンスブラシシールのもれ特性に関する数値解析 (OS8. 流体の数値計算手法と数値シミュレーション (4), オーガナイズドセッション)

李軍， 小尾晋之介

計算力学講演会講演論文集 2008, 822-823  2008

乱流混合層におけるピエゾフィルムアクチュエータを用いた混合促進 (流れの制御 (3), 一般講演)

亀谷幸憲， 中吉嗣， 深潟康二， 小尾晋之介

日本流体力学会年会講演論文集 2008, 341  2008

Turbulent structure and relaminalization of a rotating turbulent channel flow at high rotaton number

Sato S., Obi S.

2007 Proceedings of the ASME/JSME Thermal Engineering Summer Heat Transfer Conference - HT 2007 (2007 Proceedings of the ASME/JSME Thermal Engineering Summer Heat Transfer Conference - HT 2007)  1   211 - 216 2007.12

ISSN  9780791842744

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The present study reports on a series of direct numerical simulation of turbulent rotating channel flows at rotation numbers higher than those previously reported. The bulk Reynolds number (Re) was set approximately constant at 5800, while the non-dimensional rotation number Ro was increased up to 5.79. The flow visualization showed that the structure of the enlarged eddies on the pressure side, and the orientation of the structure was inclined towards downstream. The investigation of the budget of Reynolds stress transport equation indicated that the pressure transport of Reynolds stress and re-distribution term were extraordinary large at higher Ro. This led the conventional decomposition of velocity-pressure correlation terms to being not appropriate in this flow. It is suggested that the Reynolds stress modeling should better target the correlation between velocity and pressure gradient, or pressure diffusion and re-distribution terms must be handled with the same efforts, which indeed increases the task of modeling. Copyright © 2007 by ASME.

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Calculation of isotropic turbulence using a pure Lagrangian vortex method

YOKOTA RIO, SHEEL TARUN KUMAR, OBI SHINNOSUKE

Journal of Computational Physics (Journal of Computational Physics)  226 ( 2 ) 1589-1606 - 1606 2007.10

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00219991

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渦法における粘性拡散モデルの性能評価を目的として、これまで計算例がない一様等方乱流のシミュレーションを行った。乱流エネルギーおよびエンストロフィーの散逸率ならびにスペクトルの分布を調べ、従来頻繁に使用されてきたコアスプレッディングモデルに欠陥があることを指摘し、改良方法を提案した。

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Flow instability and disk vibration of shrouded corotating disk sytem

KANAGAI SHUNSUKE, SUZUKI JOE, OBI SHINNOSUKE, MASUDA SHIGEAKI

Trans. ASME, Journal of Fluids Engineering 129   1306-1313 2007.10

Research paper (scientific journal), Joint Work, Accepted

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ハードディスクドライブを模した容器内積層円盤系における空力特性と円盤振動の関係について実験的研究を行なった。PIVにより円盤表面に複数個の大規模渦構造が発生すること、それにより周期的な速度・圧力変動が発生することを見出し、円盤の固有振動とこの圧力変動の関係について論じた。

Flow instability and disk vibration of shrouded corotating disk system

Kanagai S., Suzuki J., Obi S., Masuda S.

Journal of Fluids Engineering, Transactions of the ASME (Journal of Fluids Engineering, Transactions of the ASME)  129 ( 10 ) 1306 - 1313 2007.10

ISSN  00982202

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This paper focuses on the interaction between the flow unsteadiness and disk vibration of shrouded corotating disk system to identify the nature of the flow-induced vibration of disks in the wide range of rotation speed below critical. Special attention is paid to the role of the vortical flow structure on the disk vibration and vice versa. The water test rig for optical measurement and the air test rig for hot-wire and vibration measurements are employed, both being axisymmetric models of 3.5 in. hard disk drive. Before investigating fluid-solid interaction, the velocity and vorticity fields between disks are examined by employing a particle image velocimetry, in order to check the flow within our own apparatus to have the same characteristics as those commonly accepted. In the course of this preliminary experiment, it is found that "vortical structures" reported in the previous papers based on the flow visualization are actually "vortices" in the sense that it exhibits closed streamlines with concentrated vorticity at its center when seen from an observer rotating with the structure itself. The measurements of out-of-plane displacement of the disk employing different disk materials reveal that disk vibration begins to occur even in low subcritical speed range, and amplitude of nonrepeatable run out (NRRO) can be uniquely correlated by using the ratio between the rotating speed and the critical speed. The power spectral densities of disk vibration showed that the disk vibrates as a free vibration triggered by, but not forced by, the flow unsteadiness even in the high subcritical speed range. The disk vibration has negligible effect on the vortical flow structure suggesting the soundness of the rigid disk assumption employed in the existing CFD. However, RRO has significant influence on the flow unsteadiness even if the disks are carefully manufactured and assembled. Since the RRO is unavoidable in the real disk system, the flat disk assumption should be considered more carefully. Copyright © 2007 by ASME.

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Fast Vortex method calculation using a special-purpose computer

SHEEL TARUN KUMAR, YASUOKA KENJI and OBI SHINNOSUKE

Computers and Fluids (Computers and Fluids)  36 ( 8 ) 1319-1326 - 1326 2007.09

Research paper (scientific journal), Joint Work, Accepted,  ISSN  00457930

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An application of a special purpose computer MDGRAPE2, developed for molecular dynamics simulation, to vortex flow simulation is presented. In particular, computational ambiguity inherent to the hardware is addressed and improved results are shown for calculating impinging vortex rings.

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