研究者詳細 - 芳松　克則

論文 - 芳松　克則

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Wavelet-Based Extraction of Coherent Vortices from High Reynolds Number Homogeneous Isotropic Turbulence 査読有り

K. Yoshimatsu, N. Okamoto, K. Schneider, M. Farge and Y. Kaneda

IUTAM Symposium on Computational Physics and New Perspectives in Turbulence 頁： 243-248 2008年

担当区分：筆頭著者記述言語：英語

A wavelet-based method to extract coherent vortices is applied to data of
three-dimensional incompressible homogeneous isotropic turbulence with the
Taylor micro-scale Reynolds number 471 in order to examine contribution of
the vortices to statistics on the turbulent flow. We observe a strong scaleby-
scale correlation between the velocity field induced by them and the total
velocity field over the scales retained by the data.We also find that the vortices
almost preserve statistics of nonlinear interactions of the total flow over the
inertial range.

Coherent vortices in high resolution direct numerical simulation of homogeneous isotropic turbulence: A wavelet viewpoint 査読有り

Naoya Okamoto, Katsunori Yoshimatsu, Kai Schneider, Marie Farge and Yukio Kaneda

Physics of Fluids 19 巻 ( 11 ) 頁： 115109 2007年11月

担当区分：筆頭著者記述言語：英語掲載種別：研究論文（学術雑誌）

Coherent vortices are extracted from data obtained by direct numerical simulation DNS of
three-dimensional homogeneous isotropic turbulence performed for different Taylor microscale
Reynolds numbers, ranging from Re=167 to 732, in order to study their role with respect to the
flow intermittency. The wavelet-based extraction method assumes that coherent vortices are what
remain after denoising, without requiring any template of their shape. Hypotheses are only made on
the noise that, as the simplest guess, is considered to be additive, Gaussian, and white. The vorticity
vector field is projected onto an orthogonal wavelet basis, and the coefficients whose moduli are
larger than a given threshold are reconstructed in physical space, the threshold value depending on
the enstrophy and the resolution of the field, which are both known a priori. The DNS dataset,
computed with a dealiased pseudospectral method at resolutions N=2563 , 5123 , 10243, and 20483,
is analyzed. It shows that, as the Reynolds number increases, the percentage of wavelet coefficients
representing the coherent vortices decreases; i.e., flow intermittency increases. Although the number
of degrees of freedom necessary to track the coherent vortices remains small e.g., 2.6% of N
=20483 for Re=732, it preserves the nonlinear dynamics of the flow. It is thus conjectured that
using the wavelet representation the number of degrees of freedom to compute fully developed
turbulent flows could be reduced in comparison to the standard estimation based on Kolmogorov's
theory.

Wavelet-Based Statistics in High-Resolution Direct Numerical Simulations of Three-Dimensional Homogeneous Isotropic Turbulence 査読有り

Naoya Okamoto, Katsunori Yoshimatsu and Yukio Kaneda

Frontiers of Computational Science: Proceedings of the International Symposium on Frontiers of Computational Science, Springer-Verlag 頁： 235-238 2007年6月

担当区分：筆頭著者記述言語：英語

Statistics of kinetic energy and transfer localized in space and scale are examined by using the datasets of high-resolution direct numerical simulations of three-dimensional incompressible homogeneous isotropic turbulence with the Taylor micro-scale Reynolds number up to 732. We find that the standard deviation spectra of the local energy σe and that of energy transfer σt decrease with a representative wavenumber k approximately as σe ∝ k^{−5/3} and σt ∝ k^{−1/2} in the inertial subrange, respectively.

3次元一様等法制乱流大規模直接数値計算データベースのウェーブレット解析－エネルギートランスファーについて－

岡本直也、芳松克則

乱流現象及び多自由度系の動力学, 構造と統計法則九州大学応用力学研究所研究集会報告 18ME-S7 頁： 95-101 2007年3月

Contribution of coherent and incoherent vorticity fields to high Reynolds number homogeneous isotropic turbulence : a wavelet viewpoint 査読有り

Katsunori Yoshimatsu, Naoya Okamoto, Kai Schneider, Marie Farge and Yukio Kaneda

Advances in Turbulence XI Proceedings of the 11th Euromech European Turbulence Conference, June 25-28, 2007, Porto, Portugal edited by J.M.L.M. Palma, A. Silva Lopes, Springer-Verlag 頁： 535-537 2007年

担当区分：筆頭著者記述言語：英語

A wavelet-based method to extract coherent vortices is applied to data
obtained by direct numerical simulations of three-dimensional incompressible homogeneous
isotropic turbulence for different Taylor microscale Reynolds numbers,
ranging from Rλ = 167 to 732. We find that the coherent vortices well preserve
statistics of the total flow. The incoherent flow is structureless and noise like. The
percentage of wavelet coefficients representing the coherent vortices decreases as the
Reynolds number increases.

3次元一様等方性乱流の直接シミュレーションにおけるスペクトル法と高次精度差分法との比較査読有り

芳松克則, 石原卓, 金田行雄, 中井聡, 西田秀利, 里深信行

日本機械学会論文集(B編) 69 巻 ( 679 ) 頁： 541-546 2003年

Symmetry Breaking of Radially Outgoing Flow between Two Parallel Disks 査読有り

K. Yoshimatsu and J. Mizushima

Journal of the Physical Society of Japan 72 巻 ( 12 ) 頁： 3028-3031 2003年

Surface Waves in a Square Container Due to Resonant Horizontal Oscillations 査読有り

K. Yoshimatsu and M. Funakoshi

Journal of the Physical Society of Japan 70 巻 ( 2 ) 頁： 394-406 2001年

Third-Harmonic Resonance in Two-Dimensional Faraday Waves 査読有り

K. Yoshimatsu and M. Funakoshi

Journal of the Physical Society of Japan 69 巻 ( 8 ) 頁： 2468-2478 2000年

Primary Patterns in Faraday Surface Waves at High Aspect Ratio 査読有り

K. Yoshimatsu and M. Funakoshi

Journal of the Physical Society of Japan 67 巻 ( 2 ) 頁： 451-461 1998年

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