Details of a Researcher - Obi, Shinnosuke

Papers - Obi, Shinnosuke

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S0550302 ナノ秒パルスプラズマアクチュエータによる矩形翼, 後退翼上における流体制御 ([S055-03] プラズマアクチュエータ (3))

加藤賢太郎，小尾晋之介

年次大会 2014, _S0550302--_S0550302- 2014

7・3 乱流 (7. 流体工学,< 特集> 機械工学年鑑)

小尾晋之介

日本機械学会誌 117 (1149), 521 2014

LES Study of Flow between Shrouded Co-rotating Disks

WASHIZU TOMOYA, LUBISCH FLORIAN, OBI SHINNOSUKE

Flow, Turbulence and Combustion (Flow, Turbulence and Combustion) 91 ( 3 ) 607 - 621 2013.10

Research paper (scientific journal), Joint Work, Accepted, ISSN 1386-6184

Large eddy simulations of turbulent flow between shrouded co-rotating disks, representing a simplified model of a hard disk drive, are performed. The computation domain surrounds a complete disk and is bounded at top and bottom by half a disk. Therefore, it is possible to compute the fluctuating pressure field surrounding the middle disk.
Also, the influence of the shroud geometry is taken into account by comparing a flat shroud wall and a wall with rib chambers. In the flat shroud case, the fluctuating pressure on the upper- and lower-surface of a disk indicates a strong correlation with fluid motion travelling across the disk-tip clearance region. However, in the ribbed shroud case the organized flow structure that is observed in the flat shroud case disappears and the fluctuating pressure acting on the surface of the disk is remarkably diminished.

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An experimental study on the flow behavior near the read-and-write arm in a hard disk drive model with a shroud opening

SHIRAI KATSUAKI, BUETTNER LARS, OBI SHINNOSUKE, CZARSKE JUERGEN

Microsystem Technologies (Microsystem Technologies) 19 ( 9-10 ) 1519 - 1527 2013.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 0946-7076

Complex flow inside a hard disk drive (HDD) was investigated using a simplified 3.5in model for clarifying
the mechanism causing flow-induced vibration. Flow measurements were carried out with a test rig which consisted of transparent disks, RWA and covers. The high
spatial resolution of the results was achieved using a laser
Doppler velocity profile sensor with a physical resolution
in micrometers and a velocity uncertainty of 0.2 %. The resulting velocity statistics exhibit turbulent Couette-like flow in the narrow 1 mm space between the disks and the RWA.

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Simulation and PIV experiment of the ducted water current turbine and extremely low had helical turbine

SOUNTHISACK PHOMMACHANH, OBI SHINNOSUKE, PRIYONO SUTIKNO, ARYADI SOEWONO

ASEAN Engineering Journal Part A (AUN/SEED-Net) 3 ( 2 ) 54-69 2013.09

Research paper (scientific journal), Joint Work, Accepted, ISSN 2229-127X

0617 時間分解 PIV と小型静圧プローブを用いた速度・圧力相関計測 (OS6-4 噴流, 後流およびはく離流れ現象の探求と先端的応用, OS6 噴流, 後流およびはく離流れ現象の探求と先端的応用)

河田卓也，前田星秀，小尾晋之介

流体工学部門講演会講演論文集 2013, _0617-01_-_0617-02_ 2013

1102 円筒容器内回転積層円盤間乱流における圧力変動とディスク振動の同時計測 (OS11-1 流体関連振動・騒音, OS11 流体関連振動・騒音)

高橋昌之，小尾晋之介，河田卓也

流体工学部門講演会講演論文集 2013, _1102-01_-_1102-02_ 2013

0639 自由せん断乱流中の局所圧力変動の計測 (OS6-8 噴流, 後流およびはく離流れ現象の探求と先端的応用, OS6 噴流, 後流およびはく離流れ現象の探求と先端的応用)

前田星透，河田卓也，小尾晋之介

流体工学部門講演会講演論文集 2013, _0639-01_-_0639-02_ 2013

Simultaneous measurment of fluctuating velocity and pressure using time-resolved PIV and miniature static-pressure probes

Kawata T., Obi S.

International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2013 (International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2013) 2 2013

ISSN 9780000000002

Simultaneous measurement of the fluctuating velocity and pressure is performed combining a miniature staticpressure probe and a time-resolved PIV aiming at further improvement in evaluation of the velocity-pressure correlation. Two static-pressure probes were placed in the measurement domain of the time-resolved PIV and the instantaneous velocity field and the fluctuating velocity are measured simultaneously. The instantaneous pressure filed is estimated from the measured velocity field by numerically solving a discrete Poisson equation for pressure. The values of the estimated pressure are corrected based on the pressure values which are directly measured by the static-pressure probe.

An attempt to evaluate pressure force on a flapping rigid plate using velocity data of PIV measurements

ALEXANDRE SURYADI, OBI SHINNOSUKE

ASEAN Engineering Journal 2 ( 1 ) 30-44 2012.06

Research paper (scientific journal), Joint Work

The flow field generated by a sinusoidally flapping rigid flat plate was measured using stereo particle image velocimetry to estimate the pressure field on two cross sections of the flapping plate. The pressure field was estimated by integrating the three–dimensional Poisson equation derived from the Euler equation. The solution of this Poisson equation is obtained as a function of the measured phase-averaged velocity field. Simultaneous to PIV measurements, the torque on the flapping axis, which depicts the forces acting on the wing, was measured using strain gauges. The maximum torque coefficients, observed from both methods, of each cycle are delayed from the maximum acceleration of the plate. One of the factors of the phase delay is attributed to the separation of vortex structure along the edges of the plate. After the separation point the increase of pressure drag is delayed relative to the flapping motion. At the same phase, vortex structure is generated on the leeward side of the plate at the free end. Low pressure region was observed on the leeward side of the plate which further add to the pressure drag.

1009 移動壁面を有する密閉容器内流れの渦法解析 (OS10 渦流れのダイナミクス, オーガナイズドセッション)

宮内新喜，小尾晋之介

流体工学部門講演会講演論文集 2012, 389-390 2012

Experimental and numerical investigation on a fully developed turbulent pipe flow over a semicircle orifice

Okuda S., Lepeut C.H., Rasti M., Kawata T., Obi S.

Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer (Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer) 2012-September 2504 - 2512 2012

The internal separated flow associated with remarkable mean secondary flow is investigated both experimentally and computationally. The computational investigation indicates that the commercially available RANS model group and LES provide obvious difference in terms of the prediction of the flow reattachment and recovery. On the other hand, some over-proportional magnitude of the velocity fluctuation across the mean flow direction is found by velocity measurement by stereo PIV. The recirculation region in either side of the orifice seems to be the source of the streamwise vortex that governs the development of the flow near the flow reattachment point. The considered flow serves as a useful test case for both RANS modeling and LES.

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Simultaneous measurement of fluctuating velocity and pressure using stereo-PIV and static-pressure probe in a turbulent wing-tip vortex

Kawata T., Obi S.

Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer (Proceedings of the International Symposium on Turbulence, Heat and Mass Transfer) 2012-September 2311 - 2320 2012

Simultaneous measurement of the fluctuating pressure and velocity field is performed combining a miniature static-pressure probe and a stereo-PIV. The static-pressure probe is placed just behind the velocity measuring plane illuminated by the laser sheet, and the instantaneous velocity field and the fluctuating pressure are measured simultaneously in a turbulent wing-tip vortex flow. The instantaneous pressure field is estimated by numerically solving a discrete two-dimensional Poisson equation for pressure. The result is compared with directly measured pressure for validation.

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The estimation of pressure on the surface of a flapping rigid plate by stereo PIV

Suryadi A., Obi S.

Experiments in Fluids (Experiments in Fluids) 51 ( 5 ) 1403 - 1416 2011.11

ISSN 07234864

The method to estimate the dynamic load of a flapping wing by the integration of pressure on the wing's surface is discussed. The flapping wing was modeled as a plate flapping sinusoidally in hovering condition. The flow around the flapping plate was measured using stereo PIV on multiple measurement planes along the out-of-plane direction. The phase-averaged velocity field of each measurement plane was calculated so that three-dimensional analyses could be applied. The phase-averaged pressure field was obtained from the integration of the three-dimensional Poisson equation for pressure using the available information acquired from stereo PIV measurements. The pressure field is visualized on the measurement planes. In this study, the estimated load was the torque of the axis of rotation. This torque was compared with the result from strain gauge measurements. The torque estimation, although only on a partial surface of the plate, is within reasonable agreement with the measured torque. The integration of the Poisson equation based on stereo PIV measurements and estimations of the torque shows that an increase in the torque at the start of a flapping stroke is caused by the stagnation on the surface of the plate from the flow that is induced by the leading-edge vortices. © 2011 Springer-Verlag.

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Estimation of pressure on the surface of a flapping rigid plate by stereo PIV

SURYADI ALEXANDRE, OBI SHINNOSUKE

Experiments in Fluids (Springer) 51 ( 5 ) 1403-1416 2011.10

Research paper (scientific journal), Joint Work, Accepted

The method to estimate the dynamic load of a flapping wing by the integration of pressure on the wing's surface is discussed. The flapping wing was modeled as a plate flapping sinusoidally in hovering condition. The phase-averaged pressure field was obtained from the integration of the three-dimensional Poisson equation for pressure using the available information acquired from stereo PIV measurements. The torque estimation, although only on a partial surface of the plate, is within reasonable agreement with the measured torque.

Simultaneous measurements of disk vibration and pressure fluctuation in turbulent flow developing in a model hard disk drive

KURASHIMA DAISUKE, NAKA YOSHITSUGU, FUKAGATA KOJI, OBI SHINNOSUKE

International Journal of Heat and Fluid Flow (Elsevier) 32 ( 3 ) 567–574 - 574 2011.05

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

The complex flow features inside hard disk drive models are investigated in an axisymmetric and a semi-open shroud configurations.
For the axisymmetric case, we have employed both experimental and computational approaches.
The experiment focuses on both flow dynamics and the disk vibration, where measurements of the fluctuating pressure and velocity are undertaken at some representative points.
The correlation between the disk vibration and the fluctuating pressure in the turbulent flow between disks is evident from the spectral analysis.
The experimentally observed fluctuating pressure and velocity are partly due to the disk vibration and its contribution could be estimated by comparing the experiment with the results of a large eddy simulation.
For the semi-open shroud case, although the characteristic peaks attributable to the large-scale vortical structure are still observed in the power spectra, the pressure fluctuation and the disk vibration are suppressed when the arm is inserted.

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Simultaneous measurement of velocity and fluctuating pressure in a turbulent wing-tip vortex using triple hot-film sensor and miniature total pressure probe

Kawata Takuya, Naka Yoshitsugu, Fukagata Koji, Obi Shinnosuke

Flow, Turbulence and Combustion 86 ( 3-4 ) 419 - 437 2011.04

ISSN 1386-6184

<p>We have developed a probe-system for simultaneous measurement of three velocity components and pressure in turbulent flows. A miniature total pressure probe is placed adjacent to the sensors of a triple hot-film probe in order to achieve the spatial resolution which is equivalent to that of the triple hot-film probe itself. The instantaneous static pressure is calculated from measured velocity and total pressure by means of a newly developed processing method based on the Bernoulli equation for unsteady flows. The measurements were undertaken in a turbulent wing-tip vortex flow. The look-up table method is employed for the calibration of the hot-film probe so accurate velocity data could be obtained over a wide range of the flow-attack angles. It is also demonstrated that the present probe-system is capable of measuring fluctuations in both velocity and pressure in the 20-650 Hz frequency range. The distribution of the fluctuating pressure obtained by this indirect method is in good agreement with the results from direct measurements of static pressure, demonstrating the promising performance of the present method. Furthermore, an improvement in the ability to make measurements of the velocity-pressure correlation across the wing-tip vortex is achieved. This improvement is possible because the effects of lateral velocity components are properly taken into account in the present formulation. The investigation regarding the transport equation budget for turbulent kinetic energy shows an anomalous structure of turbulence in this flow, mainly due to the meandering of the vortex, and the measurement of pressure diffusion is found to play an important role in the characterization of this kind of flow. © 2010 Springer Science+Business Media B.V.</p>

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Highly spatially resolving laser Doppler velocity measurements of the tip clearance flow inside a hard disk drive model

SHIRAI KATSUAKI, YAGUCHI YUSUKE, BUETTNER LARS, CZARSKE JUERGEN, OBI SHINNOSUKE

Experiments in Fluids (Springer) 50 ( 3 ) 573-586 - 586 2011.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 07234864

The flow in the tip clearance of a hard disk drive model has been investigated with laser Doppler techniques. The flow was driven by co-rotating disks inside a cylindrical enclosure in order to simulate a hard disk drive used for data storage devices. The main focus of the investigation was on the understanding of complex flow behavior in the narrow gap region between the disk tip and the outer shroud wall, which is supposed to be one of the causes of flow induced vibration of the disks. Experiments in the past have never been able to examine this region because of the lack of the spatial resolution of sensors in the highly three dimensional flow in the region. In the present investigation, the flow velocity in the tip clearance region was measured with optical measurement techniques for the first time.

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Simultaneous measurement of velocity and fluctuating pressure in a turbulent wing-tip vortex using triple hot-film sensor and miniature total pressure probe

KAWATA TAKUYA, NAKA YOSHITSUGU, FUKAGATA KOJI, OBI SHINNOSUKE

Flow, Turbulence and Combustion (Springer) 86 ( 3-4 ) 419-437 2011.03

Research paper (scientific journal), Joint Work

We have developed a probe-system for simultaneous measurement of three velocity components and pressure in turbulent flows. A miniature total pressure probe is placed adjacent to the sensors of a triple hot-film probe in order to achieve the spatial resolution which is equivalent to that of the triple hot-film probe itself. The investigation regarding the transport equation budget for turbulent kinetic energy shows an anomalous structure of turbulence in this flow, mainly due to the meandering of the vortex, and the measurement of pressure diffusion is found to play an important role in the characterization of this
kind of flow.

Vortex Methods for the Simulation of Turbulent Flows: Review

YOKOTA RIO, OBI SHINNOSUKE

Journal of Flow Science and Technology (Japan Society of Mechanical Engineers) 6 ( 1 ) 14-29 2011.01

Research paper (scientific journal), Joint Work, Accepted

Vortex methods are a group of Lagrangian and semi-Lagrangian methods based on the vorticity-streamfunction or vorticity-velocity formulation of the Navier-Stokes equation, and provide an interesting alternative to grid based methods for external flows dominated by unsteady vortical motion. In the present review article, we will assess the advantages and disadvantages of vortex methods for the simulation of incompressible turbulent flows, based on the speed and accuracy benchmarks that have been performed recently. Our goal is to objectively and quantitatively evaluate the performance of this non-standard method, by directly comparing it's speed and accuracy against finite difference and pseudo-spectral DNS codes under identical calculation conditions. We also present examples of vortex methods in engineering applications of turbulent flows.

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