研究者詳細 - 石原　卓

Attempts at computer-aided understanding of turbulence 査読

Yukio Kaneda, Takashi Ishihara, Koji Morishita, Yoshinori Mizuno

IUTAM SYMPOSIUM ON COMPUTATIONAL PHYSICS AND NEW PERSPECTIVES IN TURBULENCE 4 49 - 54 2008年

記述言語：英語出版者・発行元：SPRINGER

A review is presented on some attempts to understand turbulence by using high-performance computing (HPC). Among them is the study of turbulence by the direct numerical simulation (DNS) of incompressible turbulence in a periodic box with the number of grid points up to 4096(3). The DNS data shed some light on the Reynolds number (Re)-dependence of the statistics of turbulence at high Re and on the intermittency of energy dissipation. HPC is shown to be useful also for solving a multidimensional singular partial differential equation that determines the anomalous scaling of a passive scalar field advected by a random velocity field with an infinitely small correlation time.

DOI： 10.1007/978-1-4020-6472-2_7

一様等方性乱流DNSを用いたLagrange的加速度の解析(乱流基礎(4),一般講演)

高橋一樹, 石原卓

日本流体力学会年会講演論文集 2008 169 - 169 2008年

記述言語：日本語出版者・発行元：日本流体力学会

To study the properties of extreme events in Lagrangean acceleration we analyze Lagrangian data obtained from a direct numerical simulation of forced homogeneous isotropic turbulence which was performed on 1024^3 grid points with R 283. The extreme events are known to be trapping events by vortex filaments. Our analysis shows that the extreme Lagrangian accelerations are accompanied by spiral motions whose frequency is about 0.5Τ_η^1 and whose duration is less than about 10Τ_η, where Τ_η is the Kolmogorov time scale. It is found that the extreme events are strongly correlated with time variation of Lagrangian vorticities.

金田行雄, 石原卓

ながれ 26 ( 6 ) 375-383 - 383 2007年12月

記述言語：日本語掲載種別：記事・総説・解説・論説等（学術雑誌）出版者・発行元：The Japan Society of Fluid Mechanics

乱流の計算科学への試み、とくに、周期境界条件下の非圧縮一様等方性乱流の最大格子点数40963の直接数値計算 (DNS) を用いた乱流の研究について紹介する.得られた乱流DNSデータは高いレイノルズ数 (Re) における乱流統計の基本的な疑問に対する理解への貴重な手がかりを与えてくれる.その乱流統計には (i) Re-∞ における規格化されたエネルギー散逸率 (ii) 普遍平衡領域におけるエネルギースペクトル (iii) 大スケールから小スケールへのエネルギーの輸送等が含まれる

DOI： 10.11426/nagare1982.26.375

CiNii Article

22pTW-5 乱流の大規模直接数値計算データを用いたマルチフラクタル解析(乱流・渦運動,領域11,統計力学,物性基礎論,応用数学,力学,流体物理)

樋口裕孝, 石原卓

日本物理学会講演概要集 62 ( 2 ) 296 - 296 2007年8月

Small-scale statistics in high-resolution direct numerical simulation of turbulence 査読

Yukio Kaneda, Takashi Ishihara

PROGRESS IN TURBULENCE II 109 11 - + 2007年

記述言語：英語掲載種別：研究発表ペーパー・要旨（全国大会，その他学術会議）出版者・発行元：SPRINGER-VERLAG BERLIN

We performed high-resolution direct numerical simulations (DNSs) of incompressible turbulence in a periodic box with the number of grid points up to 4096(3). The DNS data shed some light on the nature, especially on the possible universality, of small-scale statistics of turbulence at high Reynolds number Re. We report some results of the analysis of the DNS data with an emphasis on the possible dependence of the statistics on Re.

Statistical property of pressure fluctuation in fully developed turbulence 査読

Yoshiyuki Tsuji, Takashi Ishihara

IUTAM SYMPOSIUM ON ELEMENTARY VORTICES AND COHERENT STRUCTURES: SIGNIFICANCE IN TURBULENCE DYNAMICS 79 163 - + 2006年

記述言語：英語出版者・発行元：SPRINGER

Pressure fluctuation is measured by using a condenser microphone and piezoresistive transducer. In order to confirm the experimental accuracy, measured data are compared with direct numerical simulation. This basic test encourages us to study small-scale statistics from the standpoint of Kohnogorov universal scaling. The power-law exponent and proportional constant of normalized pressure spectrum are discussed. The clear power law with scaling exponent -7/3 is confirmed in the range of R-lambda >= 600. These Reynolds numbers are much larger than those in velocity fluctuation for achieving the Kolmogorov scaling. The spectral constant K-p is not universal but depends on Reynolds number.

DOI： 10.1007/1-4020-4181-0_17

High-resolution direct numerical simulation of turbulence 査読

Y Kaneda, T Ishihara

JOURNAL OF TURBULENCE 7 ( 20 ) 1 - 17 2006年

記述言語：英語掲載種別：速報，短報，研究ノート等（学術雑誌）出版者・発行元：TAYLOR & FRANCIS LTD

We performed high-resolution direct numerical simulations (DNS) of incompressible turbulence in a periodic box by using a Fourier spectral method with the number of grid points up to 4096(3). The simulations consist of two series: one with k(max)eta similar to 1 ( series 1), and the other with k(max)eta similar to 2 (series 2), where k(max) is the highest wavenumber in each simulation, and. is the Kolmogorov length scale. In the 4096(3) DNS, the Taylor scale Reynolds number R-lambda similar to 1200 and the ratio of L/eta of the integral length scale L to eta is approximately 2200, in series 1. The DNS data analysis reveals simple scaling of various spectra, and also sheds some light on (i) the energy spectrum at high R-lambda, (ii) the asymptotic R-lambda-dependence of the normalized energy dissipation rate, (iii) the anomalous scaling of the spectra of energy dissipation and enstrophy, and so on. After some preliminary remarks on the methods and limitations of the DNS, this paper presents a review of the DNS data analysis. Discussions are also made on some questions invoked by the DNS.

DOI： 10.1080/14685240500256099

AM06-03-002 乱流の大規模直接数値計算に基づくマルチフラクタル解析(乱流渦構造(1),一般講演)

石原卓, 樋口裕孝, 金田行雄

日本流体力学会年会講演論文集 2006 34 - 34 2006年

記述言語：日本語出版者・発行元：日本流体力学会

Multifractal analysis is performed by using the high-resolution DNS data of turbulence with the number of grid points up to 4096^3. The analysis shows that the so-called generalized dimensions of energy dissipation and enstrophy can be obtained as almost scale-independent expornents provided that the scale is in the inertial subrange. Reynolds number dependence of multifractal measures such as the so-called f(α) spectra is discussed.

CiNii Article

CiNii Books

Statistics of energy transfer in high-resolution direct numerical simulation of turbulence in a periodic box 査読

T Aoyama, T Ishihara, Y Kaneda, M Yokokawa, K Itakura, A Un

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 12 ) 3202 - 3212 2005年12月

記述言語：英語出版者・発行元：PHYSICAL SOC JAPAN

The statistics of energy transfer is studied by using the data of a series of high-resolution direct numerical simulations of incompressible homogeneous turbulence in a periodic box with the Taylor micro-scale Reynolds number R-lambda and grid points up to approximately 1130 and 4096(3), respectively. The data show that the energy transfer T across the wave number k is highly intermittent and the skewness S and flatness F of T increase with k approximately as S proportional to (kL)(alpha S), F proportional to (kL)(alpha F) in the inertial subrange, where alpha(S) similar to 2/3, alpha(F) similar to 1 and L the characteristic length scale of energy containing eddies. The comparison between the statistics of T, the energy dissipation rate epsilon and its average epsilon(r) over a domain of scale r shows that T is less intermittent than epsilon, while there is a certain similarity between the probability distribution functions of T and epsilon(r).

DOI： 10.1143/JPSJ.74.3202

Box 乱流の大規模 DNS 結果から見た Channel 乱流

石原卓, 長田將明, 金田行雄

京都大学数理解析研究所講究録 1434 ( 1434 ) 188-194 - 194 2005年5月

結合コンパクトスキームを用いたチャネル乱流の直接数値シミュレーション

高林大作, 林一樹, 石原卓

豊田研究報告 ( 58 ) 155-160 - 160 2005年5月

Energy spectrum in the near dissipation range of high resolution direct numerical simulation of turbulence 査読

T Ishihara, Y Kaneda, M Yokokawa, K Itakura, A Uno

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 5 ) 1464 - 1471 2005年5月

記述言語：英語出版者・発行元：PHYSICAL SOC JAPAN

The energy spectrum in the near dissipation range of turbulence is studied by analyzing the data of a series of high-resolution direct numerical simulations of incompressible homogeneous turbulence in a periodic box with the Taylor micro-scale Reynolds number R-lambda and resolution ranging up to about 675 and 4096(3), respectively. The spectra in the Reynolds number range fit well to the form C(k eta)(alpha) exp(-beta k eta) in the wavenumber range 0.5 less than or similar to k eta less than or similar to 1.5, where eta is the Kolmogorov dissipation length scale and C, alpha and beta are constants independent of k. The values of alpha and beta decrease monotonically with R-lambda, and they are consistent with the conjecture that they approach to constants as R-lambda -> infinity, but the approach, especially that of beta, is slow.

DOI： 10.1143/JPSJ.74.1464

AM05-02-001 乱流のUltraDNSデータ解析 : 乱流の慣性小領域におけるエネルギー流束とエネルギー散逸(地球シミュレータを用いた大規模計算,一般講演)

石原卓, 青山知弘, 金田行雄

日本流体力学会年会講演論文集 2005 53 - 53 2005年

記述言語：日本語出版者・発行元：日本流体力学会

Energy flux in turbulence from scales larger than a filter size γ to small scales is given by T(x, t)=-Τ_<ij>S^^-_<ij>, where Τ_<ij> is the subgrid stress and S^^-_<ij> is the resolved strain-rate tensor. The statistics of T is studied by using the data of a series of high-resolution direct numerical simulations of incompressible turbulence in a periodic box with the number of grid points up to 4096^3. The data show that T is highly intermittent and the skewness S and flatness F of T increase with the wavenumber κ(∝1/γ) approximately as S ∝(κL)^<αS> F ∝(κL)^<αF> in the inertial subrange, where α_S and α_F are constants independent of R_λ, and L is the characteristic length scale of energy containing eddies. The relation between the statistics of T, the energy dissipation rate ε and its local average ε_γ over a domain of scale r is also studied; T is less intermittent than ε and there is a certain similarity in the probability distribution functions of T and ε_γ.

CiNii Article

CiNii Books

Scalability of hybrid programming for a CFD code on the Earth Simulator

K Itakura, A Uno, M Yokokawa, T Ishihara, Y Kaneda

PARALLEL COMPUTING 30 ( 12 ) 1329 - 1343 2004年12月

記述言語：英語出版者・発行元：ELSEVIER SCIENCE BV

The Earth Simulator (ES) is an SMP cluster system. There are two types of parallel programming models available on the ES. One is a flat programming model, in which a parallel program is implemented by MPI interfaces only, both within an SMP node and among nodes. The other is a hybrid programming model, in which a parallel program is written by using thread programming within an SMP node and MPI programming among nodes simultaneously. It is generally known that it is difficult to obtain the same high level of performance using the hybrid programming model as can be achieved with the flat programming model.
In this paper, we have evaluated scalability of the code for direct numerical simulation of the Navier-Stokes equations on the ES. The hybrid programming model achieves the sustained performance of 346.9Gflop/s, while the flat programming model achieves 296.4Gfiop/s with 16 PNs of the ES for a DNS problem size of 256 3. For small scale problems, however, the hybrid programming model is not as efficient because of microtasking overhead. It is shown that there is an advantage for the hybrid programming model on the ES for the larger size problems. (C) 2004 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.parco.2004.09.006