Details of a Researcher - Obi, Shinnosuke

Papers - Obi, Shinnosuke

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Drag reduction in channel flow by traveling wave-like surface heating/cooling

MAMORI HIROYA, FUKAGATA KOJI, OBI SHINNOSUKE

6th International Symposium on Turbulent Shear Flow Phenomena (6th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2009) 2009-June 581-586 - 586 2009.06

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

Reduction of skin-friction drag in a channel flow by traveling wave-like surface heating/cooling is investigated by means of linear analysis and direct numerical simulation. The linear analysis reveals that a downstream traveling wave can reduce the skin-friction drag. Due to non-quadrature between the streamwise and the wall-normal velocity disturbances induced by the buoyancy force, negative Reynolds shear stress is created in the regions near the walls, which contributes to the skin-friction drag reduction. The direct numerical simulation shows that a traveling wave at a high wavenumber slightly reduces the friction drag in a fully developed turbulent channel flow. The velocity fluctuations and the Reynolds shear stress are slightly attenuated by this control. The friction drag increases for larger magnitudes and lower wavenumbers of the traveling waves. Non-zero mean temperature profile is created due to the turbulent heat flux induced by the control.

Velocity-pressure correlation measurements in complex free shear flows

NAKA YOSHITSUGU, OBI SHINNOSUKE

International Journal of Heat and Fluid Flow (Elsevier) 30 ( 3 ) 411-420 2009.06

Research paper (scientific journal), Joint Work, Accepted

Simultaneous measurements of fluctuating velocity and pressure were performed in various turbulent free shear flows including a turbulent mixing layer and the wing-tip vortex trailing from a NACA0012 half-wing. Two different methods for fluctuating static pressure measurement were considered: a direct method using a miniature Pitot tube and an indirect method where static pressure was calculated from total pressure. The pressure obtained by either of these methods was correlated with the velocity measured by an X-type hot-wire probe. The results from these two techniques agreed with each other in the turbulent mixing layer. In the wing-tip vortex case, however, some discrepancies were found, although overall characteristics of the pressure-related statistics were adequately captured by both methods.

Modification of flow around a circular cylinder using porous media

NAITO HIROSHI, FUKAGATA KOJI, OBI SHINNOSUKE

6th International Symposium on Turbulent Shear Flow Phenomena (6th International Symposium on Turbulence and Shear Flow Phenomena, TSFP 2009) 2009-June 1019-1024 - 1024 2009.06

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

Flow around a circular cylinder having a porous surface is studied numerically by means of direct numerical simulation (DNS) and large eddy simulation (LES). The flow in the porous media is represented by a spatially-averaged (i.e., macroscopic) model. The parameters of the most effective porous media are found from a two-dimensional parametric test at the Reynolds number, based on the free stream velocity and the diameter of cylinder, of Re = 1000. The lift force fluctuation is notably reduced in the case of thicker porous surface. The DNS of three-dimensional flow at Re = 1000 reveals that the porous surface works to stabilize the shear layer. The LES at a very high Reynolds number (Re = 105) shows that the vortex shedding is completely suppressed by the porous media, which supports the experimental observation by Sueki et al. (2007). Simulations at different Reynolds numbers show that the stabilization effect works better at higher Reynolds numbers.

Simultaneous measurement of velocity and pressure in a wing-tip vortex

NAKA YOSHITSUGU, AZEGAMI SUGURU, KAWATA TAKUYA, FUKAGATA KOJI, OBI SHINNOSUKE

Journal of Fluid Science and Technology (JSME) 4 ( 1 ) 107-115 2009.02

Research paper (scientific journal), Joint Work, Accepted

Simultaneous measurements of fluctuating velocity and pressure have been conducted in the near field of a wing-tip vortex trailing from a NACA0012 half wing. In the
vortex core, the time-averaged streamwise velocity shows a wake-like profile which exhibits a deficit by approximately 25% of free stream velocity. The meandering of the vortex is evident from both velocity and pressure measurements: The power spectral density (PSD) of the transverse velocity fluctuation increases in the lower frequency range, and the distribution of the pressure fluctuation exhibits an elongated shape in the z direction as well as two peaks slightly off from the vortex center. The distribution of the measured velocity-pressure correlation varies significantly near the center of the
vortex especially in downstream locations.

Fast multipole methods on a cluster of GPUs for the meshless simulation of turbulence

YOKOTA R., NARUMI T., SAKAMAKI R., KAMEOKA S., OBI S., YASUOKA K.

Computer Physics Communications (Computer Physics Communications) 180 ( 11 ) 2066-2078 - 2078 2009

Research paper (scientific journal), Joint Work, Accepted, ISSN 00104655

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平行平板間乱流における渦法の検証 (解析・予測・制御乱流の予測とモデリング (1), 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 2009, 253 2009

等温度差チャネル流における進行波状吹出し・吸込みを用いた摩擦抵抗低減と伝熱促進の同時制御

東孝祐，守裕也，深潟康二，小尾晋之介

日本伝熱シンポジウム講演論文集第 46 回日本伝熱シンポジウム, 77-77 2009

レイノルズ平均乱流モデルの現状と展望

小尾晋之介

化学工学= Chemical engineering 73 (5), 214-217 2009

Comparing vortex methods and finite difference methods in a homogeneous turbulent shear flow

横田理央，小尾晋之介

International Journal for Numerical Methods in Fluids 63 (7) (International Journal for Numerical Methods in Fluids) 63 ( 7 ) 828 - 846 2009

ISSN 02712091

The vortex method is applied to the calculation of a homogeneous shear turbulence, and compared with a finite difference code using identical calculation conditions. The core spreading method with spatial adaptation is selected as the viscous diffusion scheme of the vortex method. The shear rate is chosen so that it matches the maximum value observed in a fully developed channel flow. The isosurface, anisotropy tensors, and joint probability density functions reflect the ability of the present vortex method to quantitatively reproduce the anisotropic nature of strongly sheared turbulence, both instantaneously and statistically. Copyright © 2009 John Wiley & Sons, Ltd.

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405 L929 線維芽細胞の増殖性・接着性に及ぼす基材表面凹凸形状の影響 (生体・医療材料 II, 生体・医療材料, オーガナイスドセッション 10)

長井篤，斎藤万里雄，宮田昌悟，小茂鳥潤，小尾晋之介

学術講演会講演論文集 58, 65-66 2009

0507 円柱周りのべき乗則流体の流れの数値シミュレーション (OS5-2 非ニュートン流体の流動現象, オーガナイズドセッション)

犬飼翼，内藤弘士，深潟康二，小尾晋之介

流体工学部門講演会講演論文集 2009, 223-224 2009

0229 熱線流速計と小型静圧プローブを用いた変動速度・圧力の同時測定 (OS2-6 乱流の計測・解析・制御, オーガナイズドセッション)

中吉嗣，河田卓也，深潟康二，小尾晋之介

流体工学部門講演会講演論文集 2009, 147-148 2009

0128 プラズマアクチュエータを用いた吹出し・吸込みによる翼端渦の抑制 (OS1-5 噴流, 後流および剥離流れの流動解析と応用, オーガナイズドセッション)

長谷部仁美，中吉嗣，深潟康二，小尾晋之介

流体工学部門講演会講演論文集 2009, 57-58 2009

プラズマアクチュエータによる三次元撹乱を用いた円柱周りの流れの制御 (解析・予測・制御流れの制御 (1), 一般講演)

井上薫，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 2009, 350 2009

Lagrangian Vortex Methods in Turbulent Channel Flows

Yokota R., Fukagata K., Obi S.

Springer Proceedings in Physics (Springer Proceedings in Physics) 132 2009

ISSN 09308989

In our present study, we compare the turbulent statistics obtained from a vortex method calculation with a finite difference calculation for the turbulent channel flow. The present vortex method is a standard vortex particle method, which uses the core spreading method with spatial adaptation [1] as the diffusion scheme. The Reynolds number was Reb = 5600 and the calculation domain was 3δ × 2δ ×3 δ ×, where δ is the channel half width. The mean velocity profile after one wash-out time is shown in Fig. 1(a), while the mean velocity gradient and Reynolds stress after one wash-out time are shown in Fig. 1(b). The results of the vortex method show an excessive production of Reynolds stress in the viscous layer.

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On the weak-equilibrium condition for derivation of algebraic heat flux model

QIU JIFENG, OBI SHINNOSUKE, TOMAS B. GATSKI

International Journal of Heat and Fluid Flow (Elsevier) 29 ( 6 ) 1628-1637 - 1637 2008.12

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

Analogous to an algebraic Reynolds stress model, the algebraic heat flux model (AHFM) is derived from a
second-moment closure by invoking the weak-equilibrium condition. The present study investigates this condition in detail as it applies to the advection and diffusive-transport terms. For the advection term, the correct form of this condition in non-inertial frames is obtained by means of an invariant Euclidean transformation. The validity of the diffusive-transport condition is examined through an a priori test using a DNS database for rotating turbulent channel flow with heat transfer. It is shown that the weak-equilibrium condition applied to diffusive-transport term tends to fail in the near-wall region. An alternative form is proposed that is based on an asymptotic analysis of the transport equation budget in the near wall region. An evaluation of proposed form shows that it has the potential to improve the predictive ability of an ARSM for flows involving system rotation and/or streamline curvature.

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Simultaneous measurement of velocity and pressure in a wingtip vortex

AZEGAMI SUGURU, KAWADA TAKUYA, NAKA YOSHITSUGU, OBI SHINNOSUKE

7th JSME-KSME Thermal and Fluids Engineering Conference 2008.10

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

Simultaneous measurements of fluctuating velocity and pressure have been conducted in the near field of a wing-tip vortex trailing from a NACA0012 half wing. In the vortex core, time-averaged streamwise velocity shows a wake-like profile which exhibits a deficit by approximately 25% of free stream velocity. The meandering of vortex is evident from both velocity and pressure measurements: The PSD of transverse velocity fluctuation increases in lower frequency range, and the distribution of pressure fluctuation exhibit elongated shape in z-direction and two peaks slightly off from the vortex center. The measured velocity-pressure correlation shows significant gradient near the center of the vortex especially in a downstream location.

The effect of wing tip vortex to force generation of a flapping wing

SURYADI ALEXANDRE, ISHII TAKAYUKI, OBI SHINNOSUKE

7th JSME-KSME Thermal and Fluids Engineering Conference 2008.10

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

Flow visualization and velocity measurements with particle image velocimetry (PIV) have been conducted in the near field of the tip of a sinusoidally flapping plate with the initial condition of fluid at rest. Experiments were conducted at Reynolds number of 1580 and 3160. We visualized the evolution of vortices and performed force calculation based on stereo PIV velocity field data. Three planes near the wing tip were measured with PIV and we found that several features of the flow from PIV measurements are similar with flow visualization.

The pressure-velocity correlation in the turbulent wingtip vortex flow

ISHII TAKAYUKI, SURYADI ALEXANDRE, OBI SHINNOSUKE

7th JSME-KSME Thermal and Fluids Engineering Conference 2008.10

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

The present study attempts to characterize the fluctuating pressure field in turbulent flow associated with strong streamwise vortex. The instantaneous velocity distribution is measured by a stereoscopic PIV and the corresponding pressure field is obtained as a solution of discrete Poisson equation. The results are presented for the
statistics of turbulence containing the pressure velocity correlation. It is indicated that the distribution of normal components of Reynolds stress are attributable to the magnitude of velocity pressure-gradient correlation terms in the corresponding transport equations.

Numerical simulation of a plane mixing layer with periodic excitation

SHIMADA KOSUKE, FUKAGATA KOJI, OBI SHINNOSUKE

7th JSME-KSME Thermal and Fluids Engineering Conference 2008.10

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

We perform direct numerical simulation (DNS) of a plane mixing layer under a predetermined control. The inlet velocity is given as the sum of a hyperbolic-tangent base flow and random disturbances. The base flow is periodically excited to mimic the actuation in the experiment. The Reynolds number (Re) based on the velocity difference and the vorticity thickness is 400. The effects of excitation amplitude and frequency are systematically investigated and it is found that the mixing is enhanced for lower frequency, while suppressed for higher frequency. Through the examination of flow statistics, we clarify the mechanisms of mixing enhancement/suppression due to the control input.

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