Papers - Obi, Shinnosuke

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

　View Summary

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。

• Access to Document (DOI)

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

　View Summary

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

　View Summary

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.

• Access to Document (DOI)

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

　View Summary

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.

• Access to Document (DOI)

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

OMORI TAKESHI, JAKIRLIC SUAD, TROPEA CAMERON, OBI SHINNOSUKE

Proceedings of 5th Int. Symp. Turbulent Shear Flow Phenomena  2007.08

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

　View Summary

円柱が、一様流中に置かれた場合と、一様せん断流中に置かれた場合で、流れとの力学的な相互作用にどのような変化が生れるかをLESにより詳細に調べた。従来、混相流中での粒子の運動を議論する際に焦点とされた浮力項が主流のせん断によって発生する機構を明らかにすることができた。

Evaluation of diffusion/transport constraints for ARSM in calculation of fully developed rotating channel flow

QIU JIFENG, OBI SHINNOSUKE, GATSKI THOMAS B.

Proceedings of 5th Int. Symp. Turbulent Shear Flow Phenomena  2007.08

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

　View Summary

従来の代数応力モデルを回転系に適用した際に問題となる座標系依存性について調べ、特に壁面近傍における拡散項の振る舞いに大きな問題が発生することを示した。また、改良モデルを提案し、DNSデータベースによる評価を行なった。

Pure Lagrangian vortex methods for the simulation of decaying isotropic turbulence

YOKOTA RIO, OBI SHINNOSUKE

Proceedings of 5th Int. Symp. Turbulent Shear Flow Phenomena  2007.08

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

　View Summary

一様等方性乱流場を渦法により計算し、従来行なわれることのなかったDNSとの直接的な比較を通じて、双方の手法の比較を行なうとともに、渦法でこれまで評価が十分にされなかったエネルギー保存性などについて検討を加えた。

Development of a miniature probe for velocity-pressure correlation measurement

NAKA YOSHITSUGU, OBI SHINNOSUKE, MASUDA SHIGEAKI

Proceedings of 5th Int. Symp. Turbulent Shear Flow Phenomena  2007.08

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

　View Summary

乱流中で変動する速度と圧力を同時に計測し、速度－圧力相関項を評価する目的で、超ミニチュア圧力プローブを開発した。X型熱線風速計プローブとの組み合わせにより、従来の方法に比べて空間解像度を格段に改良した。ノイズ除去方法について系統的な検討を加えた。

Computational analysis of the shear-induced lift force on a cylindrical particle by means of LES with relevance to particle-laden liquid flow in an upward duct

OMORI TAKESHI, JAKIRLIC SUAD, OBI SHINNOSUKE, TROPEA CAMERON

Proceedings of 6th International Conference on Multiphase Flow  2007.07

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

　View Summary

固気混相乱流中における固体粒子の運動を評価する目的でLESを実行し、主流中にせん断が含まれる場合に発生する浮力の効果について詳細に調べた。

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

SATO SHINICHIRO, OBI SHINNOSUKE

Proceedings of 2007 ASME-JSME Thermal Engineering Summer Heat Transfer Conference (ASME)   2007.07

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

　View Summary

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.

A Validation of Viscous Dissipation Models for Fast Vortex Methods in Simulations of Decaying Turbulence

TOTSUKA YOSHITAKA, OBI SHINNOSUKE

Journal of Fluid Science and Technology (日本機械学会)  2 ( 1 ) 248-257 2007.06

Research paper (scientific journal), Joint Work, Accepted

　View Summary

For realistic turbulent flow simulations, quantitative representation of turbulent flow dynamics is desired.
In the present study, two-dimensional homogeneous isotropic turbulence is simulated by using a grid-free vortex method to focus on the viscous dissipation process.
The results are compared with those of spectral DNS.
Two viscous diffusion models, i.e., a core spreading model and Moving Particle Semi-implicit(MPS) Laplacian model, are compared.
For the former model, merging and insertion of particles are incorporated to ensure uniform distribution of vortex elements.
It is shown that the MPS Laplacian model is superior to the conventional core spreading model in terms of the decay rate of enstrophy and energy spectra.
Furthermore, the computational time is remarkably reduced by using a Fast Multipole Method(FMM), while retaining accuracy.

渦法による一様せん断流の解析 (乱流の予測とモデリング (4), 一般講演)

横田理央， 小尾晋之介

日本流体力学会年会講演論文集 2007, 195  2007

代数熱流束乱流モデルのユークリッド普遍性について (乱流の予測とモデリング (3), 一般講演)

邱継峰， 小尾晋之介

日本流体力学会年会講演論文集 2007, 191  2007

変動全圧・速度の同時計測による速度・圧力相関の計測 (境界層・せん断流・遷移 (4), 一般講演)

中吉嗣， 小尾晋之介

日本流体力学会年会講演論文集 2007, 155  2007

FPB 処理を施したチタン合金表面における細胞接着性の評価

田口智之， 小茂鳥潤， 小尾晋之介

JCOM 講演論文集 36, 339-343  2007

663 回転チャネル乱流の再層流化に関する DNS (OS2-1 乱流のモデリングとシミュレーション)

佐藤眞一郎， 小尾晋之介

東海支部総会講演会講演論文集 2007.56, 325-326  2007

662 渦法によるメッシュフリー乱流解析 (OS2-1 乱流のモデリングとシミュレーション)

横田理央， 小尾晋之介

東海支部総会講演会講演論文集 2007.56, 323-324  2007

329 乱流混合層における変動全圧・速度の同時計測 (2)(OS3-7 噴流, 後流, せん断流の構造・普遍的特性 (せん断流 1), OS3 噴流, 後流, せん断流の構造・普遍的特性)

中吉嗣， 小尾晋之介

流体工学部門講演会講演論文集 2007, _329-1_-_329-4_  2007

311 翼端渦の乱流速度場計測 (2)(OS3-3 噴流, 後流, せん断流の構造・普遍的特性 (後流 3・噴流 1), OS3 噴流, 後流, せん断流の構造・普遍的特性)

畔上俊， 中吉嗣， 小尾晋之介

流体工学部門講演会講演論文集 2007, _311-1_-_311-4_  2007

The pressure-velocity correlation in oscillatory turbulent flow between a pair of bluff bodies

OBI SHINNOSUKE, TOKAI NORIHIKO

International Journal of Heat and Fluid Flow (Elsevier)  27 ( 5 ) 768-776 - 776 2006.10

Research paper (scientific journal), Joint Work, Accepted,  ISSN  0142727X

　View Summary

The velocity field obtained with PIV was averaged with respect to either time or phase of periodic pressure oscillation induced by vortex shedding from the bluff body, i.e., Reynolds decomposition or three-level decomposition. The effect of organized vortex motion caused strong correlations between velocity and pressure gradient when observed from the framework of the Reynolds averaging.

• Access to Document (DOI)