Faculty Profiles - ISHIHARA Takashi

Multifractal analysis by using high-resolution direct numerical simulation of turbulence Reviewed

Takashi Ishihara, Hirotaka Higuchi

IUTAM SYMPOSIUM ON COMPUTATIONAL PHYSICS AND NEW PERSPECTIVES IN TURBULENCE 4 61 - 66 2008

Language：English Publisher：SPRINGER

Multifractal analysis based on the energy dissipation epsilon and the enstrophy Omega in isotropic turbulence is made by using high-resolution direct numerical simulation of turbulence with the number of grid points up to 20483. The analysis shows that the singularity exponents alpha and alpha' that characterize the intermittencies associated with epsilon and Omega, respectively, agree well with each other in the inertial subrange. This result is consistent with log epsilon(r) and log Omega(r) correlating well with each other for the scale r in the inertial subrange, where the subscript denotes the local average over a cubic domain of size r.

DOI： 10.1007/978-1-4020-6472-2_9

Analysis of Lagrangian acceleration by DNS of isotropic turbulence

Takahashi Kazuki, Ishihara Takashi

2008 169 - 169 2008

Language：Japanese

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.

CiNii Books

Attempts at Computational Science of Turbulence Invited

KANEDA Yukio, ISHIHARA Takashi

nagare 26 ( 6 ) 375-383 - 383 2007.12

Language：Japanese Publishing type：Article, review, commentary, editorial, etc. (scientific journal) Publisher：The Japan Society of Fluid Mechanics

A review is presented on attempts to understand turbulence by using high-performance computing. An emphasis is puton the study of turbulence by the direct numerical simulation (DNS) of incompressible turbulence in a periodic boxwith the number of grid points up to 4096³. The DNS data shed some light on the basic questions on the statisticsof turbulence at high Reynolds number Re. The statistics include (i) the normalized mean rate of kinetic energydissipation in the limit Re→→, (ii) the energy spectrum in the universal equilibrium range, (iii) intermittency of thenergy dissipation rate, and (iv) energy transfer from large to small scales.

DOI： 10.11426/nagare1982.26.375

22pTW-5 Multifractal analysis of turbulence by high resolution DNS

Higuchi Hirotaka, Ishihara Takashi

Meeting abstracts of the Physical Society of Japan 62 ( 2 ) 296 - 296 2007.8

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

Yukio Kaneda, Takashi Ishihara

PROGRESS IN TURBULENCE II 109 11 - + 2007

Language：English Publishing type：Research paper, summary (national, other academic conference) Publisher：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.

High-resolution direct numerical simulation of turbulence Reviewed

Y Kaneda, T Ishihara

JOURNAL OF TURBULENCE 7 ( 20 ) 1 - 17 2006

Language：English Publishing type：Rapid communication, short report, research note, etc. (scientific journal) Publisher：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

Statistical property of pressure fluctuation in fully developed turbulence Reviewed

Yoshiyuki Tsuji, Takashi Ishihara

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

Language：English Publisher：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

AM06-03-002 Multifractal Analysis by Using High-Resolution Direct Numerical Simulation of Turbulence

Ishihara Takashi, Higuchi Hirotaka, Kaneda Yukio

2006 34 - 34 2006

Language：Japanese

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 Books

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

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 12 ) 3202 - 3212 2005.12

Language：English Publisher：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 2005.5

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

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

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 74 ( 5 ) 1464 - 1471 2005.5

Language：English Publisher：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

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 2005.5

AM05-02-001 Data analysis based on the ultra DNS of turbulence : Energy flux and dissipation in the inertial subrange of turbulence

Ishihara Takashi, Aoyama Tomohiro, Kaneda Yukio

2005 53 - 53 2005

Language：Japanese

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 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 2004.12

Language：English Publisher：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