Faculty Profiles - ISHIHARA Takashi

Papers - ISHIHARA Takashi

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Numerical analysis of intermediate species diffusion effect on low temperature oxidation in a homogeneous n-heptane mixture Reviewed

Atsushi Teraji, Masashi Nishida, Takahiro Morikawa, Takashi Ishihara, Yukio Kaneda

Nihon Kikai Gakkai Ronbunshu, B Hen/Transactions of the Japan Society of Mechanical Engineers, Part B 77 ( 779 ) 1592 - 1600 2011

Language：Japanese Publishing type：Research paper (scientific journal)

Two-dimensional direct numerical simulation (DNS) was applied to auto-ignition of n-heptane/air mixture. The diffusion of intermediate species was studied in terms of the influence on the ignition delay. The chemical reaction process. The simplified reaction mechanism was used in this study. Likewise, the influence of turbulence was investigated by comparing the results of 0 dimensional simulation and two-dimensional direct simulation of non-turbulence condition. In conclusions, the ignition delay was strongly affected by the different diffusion speeds of intermediate species. It was shown that the outflow of OH radical having larger diffusion coefficient decreases the reaction rate at the high temperature point. On the contrary, the reaction rate was enhanced by the influx of OH radical at the low temperature point. © 2011 The Japan Society of Mechanical Engineers. © 2012 The Japan Society of Mechanical Engineers.

DOI： 10.1299/kikaib.77.1592

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Study of High-Reynolds Number Isotropic Turbulence by Direct Numerical Simulation Reviewed

Takashi Ishihara, Toshiyuki Gotoh, Yukio Kaneda

ANNUAL REVIEW OF FLUID MECHANICS 41 165 - 180 2009

Language：English Publisher：ANNUAL REVIEWS

We review studies of the statistics of isotropic turbulence in an incompressible fluid at high Reynolds numbers using direct numerical simulation (DNS) from the viewpoint of fundamental physics. The Reynolds number achieved by the largest DNS, with 4096(3) grid points, is comparable with the largest Reynolds number in laboratory experiments. The high-quality DNS data in the inertial subrange and the dissipative range enable the examination of detailed statistics at small scales, such as the normalized energy-dissipation rate, energy and energy-flux spectra, the intermittency of the velocity gradients and increments, scaling exponents, and flow-field structure. We emphasize basic questions of turbulence, universality in the sense of Kolmogorov's theory, and the dependence of the statistics on the Reynolds number and scale.

DOI： 10.1146/annurev.fluid.010908.165203

Web of Science

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Examination of Kolmogorov's 4/5 law by high-resolution direct numerical simulation data of turbulence Reviewed

Yukio Kaneda, Junya Yoshino, Takashi Ishihara

JOURNAL OF THE PHYSICAL SOCIETY OF JAPAN 77 ( 6 ) 064401 2008.6

Language：English Publishing type：Research paper (scientific journal) Publisher：PHYSICAL SOC JAPAN

Kolmogorov's 4/5 law is examined quantitatively by using the data of direct numerical simulations of incompressible turbulence in a periodic box with the number of grid points and the Taylor micro-scale Reynolds number 2048(3) and R-gimel approximate to 732, respectively. The examination is based on a generalization of the Karman-Howarth-Kolmogorov (KHK) equation for isotropic turbulence to anitropic turbulence. An emphasis is put on the influence of the finite Reynolds number, length-scale and the weak but finite anisotropy. The analysis of the DNS data gives a quantitative idea on the role of the viscous and forcing terms in the KHK equation. It also suggests that the anisotropy has substantial influence on the 4/5 law for a wide scale-range.

DOI： 10.1143/JPSJ.77.064401

Web of Science

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Small-scale statistics in high-resolution direct numerical simulation of turbulence: Reynolds number dependence of one-point velocity gradient statistics Reviewed

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

JOURNAL OF FLUID MECHANICS 592 335 - 366 2007.12

Language：English Publishing type：Research paper (scientific journal) Publisher：CAMBRIDGE UNIV PRESS

One-point statistics of velocity gradients and Eulerian and Lagrangian accelerations are studied by analysing the data from high-resolution direct numerical simulations (DNS) of turbulence in a periodic box, with up to 4096 3 grid points. The DNS consist of two series of runs; one is with k(max)eta similar to 1 (Series 1) and the other is with k(max)eta similar to 2 (Series 2), where k(max) is the maximum wavenumber and eta the Kolmogorov length scale. The maximum Taylor-microscale Reynolds number R-lambda in Series 1 is about 1130, and it is about 675 in Series 2. Particular attention is paid to the possible Reynolds number (Re) dependence of the statistics. The visualization of the intense vorticity regions shows that the turbulence field at high Re consists of clusters of small intense vorticity regions, and their structure is to be distinguished from those of small eddies. The possible dependence on Re of the probability distribution functions of velocity gradients is analysed through the dependence on R-lambda of the skewness and flatness factors (S and F). The DNS data suggest that the R-lambda dependence of S and F of the longitudinal velocity gradients fit well with a simple power law: S similar to -0.32R(lambda)(0.11) and F similar to 1.14(lambda)(0.34), in fairly good agreement with previous experimental data. They also suggest that all the fourth-order moments of velocity gradients scale with R-lambda similarly to each other at R-lambda > 100, in contrast to R-lambda < 100. Regarding the statistics of time derivatives, the sccond-order time derivatives of turbulent velocities are more intermittent than the first-order ones for both the Eulerian and Lagrangian velocities, and the Lagrangian time derivatives of turbulent velocities are more intermittent than the Eulerian time derivatives, as would be expected. The flatness factor of the Lagrangian acceleration is as large as 90 at R-lambda approximate to 430. The flatness factors of the Eulerian and Lagrangian accelerations increase with R-lambda approximately proportional to R-lambda(alpha E) and R-lambda(alpha L), respectively, where alpha(E) approximate to 0.5 and alpha(L) approximate to 1.0, while those of the second-order time derivatives of the Eulerian and Lagrangian velocities increases approximately proportional to R-lambda(beta E) and R-lambda(beta L), respectively, where beta(E) approximate to 1.5 and beta(L) approximate to 3.0.

DOI： 10.1017/S0022112007008531

Web of Science

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Introduction to Spectral Methods

Ishihara Takashi

Bulletin of the Japan Society for Industrial and Applied Mathematics 15 ( 3 ) 280 - 281 2005

Similarity scaling of pressure fluctuation in turbulence

Yoshiyuki Tsuji, Takashi Ishihara

Physical Review E - Statistical, Nonlinear, and Soft Matter Physics 68 ( 2 2 ) 2003.8

Publishing type：Research paper (scientific journal)

The static pressure fluctuation in a fully developed turbulence was measured. The aim was to determine how the spectral form varies depending on the Reynolds number. In particular, the spectral exponent and constant Kp were studied from the standpoint of Kolmogorov scaling. Probability density functions were computed and compared with DNS in order to ascertain the qualitative accuracy.

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