渡邉 智昭 (Tomoaki Watanabe)

X. Zhang, T. Watanabe, and K. Nagata Reynolds number dependence of the turbulent/non-turbulent interface in temporally developing turbulent boundary layers Journal of Fluid Mechanics, 964 A8 2023 This article may be found at  https://doi.org/10.1017/jfm.2023.329 . Accepted manuscript is available here.  This version is free to view and download for private research and study only.  Abstract Direct numerical simulations (DNS) of temporally developing turbulent boundary layers are performed with a wide range of Reynolds numbers based on the momentum thickness  Reθ=2000-13000 for investigating the Reynolds number dependence of the turbulent/non-turbulent interface (TNTI) layer. The grid spacing in the DNS is determined carefully such that small-scale turbulent motions near the TNTI are well resolved. The outer edge of the TNTI layer, called the irrotational boundary, is detected with vorticity magnitude. The mean thicknesses of the TNTI layer, δTNTI, turbulent sublayer,  δTSL , and viscou

K. Nakamura, T. Watanabe, and K. Nagata The response of small-scale shear layers to perturbations in turbulence Journal of Fluid Mechanics, 963 A31 2023 (Open Access) This article may be found at https://doi.org/10.1017/jfm.2023.316 . The article is also available  here .  Abstract The perturbation response of small-scale shear layers in turbulence is investigated with direct numerical simulations (DNS). The analysis of shear layers in isotropic turbulence suggests that the typical layer thickness is about four times the Kolmogorov scale η. Response for sinusoidal perturbations is investigated for an isolated shear layer, which models a mean flow around the shear layers in turbulence. The vortex formation in the shear layer is optimally promoted by the perturbation whose wavelength divided by the layer thickness is about 7. These results indicate that the small-scale shear instability in turbulence is efficiently promoted by velocity fluctuations with a wavelength of about 30η. Further

K. Nakamura, T. Watanabe, and K. Nagata Turbulent/turbulent interfacial layers of a shearless turbulence mixing layer in temporally evolving grid turbulence Physics of Fluids, 35 045117 2023 This article may be found at  https://doi.org/10.1063/5.0141253 . The PDF is also available  here .  This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.  Abstract Turbulent/turbulent interfacial (TTI) layers are investigated with direct numerical simulation of temporally evolving grid turbulence. The present study considers a temporally evolving wake of two parallel-bar grids with different mesh sizes, which generate homogeneous isotropic turbulent regions with large and small turbulent kinetic energies (TKE). A shearless mixing layer of turbulence forms between the large- and small-TKE regions. The TTI layer bounded by the large- or small-TKE region is identified with a passive scalar field, and the flow statistics are eva

Y. Zheng, K. Nakamura, K. Nagata, and T. Watanabe Unsteady dissipation scaling in static- and active-grid turbulence Journal of Fluid Mechanics, 956 A20 2022 This article may be found at  https://doi.org/10.1017/jfm.2022.937 . Accepted manuscript is available here.  This version is free to view and download for private research and study only.  Abstract A new time-dependent analysis of the global and local fluctuating velocity signals in grid turbulence is conducted to assess the scaling laws for non-equilibrium turbulence. Experimental datasets of static- and active-grid turbulence with different Rossby numbers Ro(=U/ΩM: U is the mean velocity, Ω is the mean rotation rate and M is the grid mesh size) are considered. Although the global (long-time-averaged) non-dimensional dissipation rate Cε is independent of the Reynolds number Reλ based on the global Taylor microscale, the local (short-time-averaged) non-dimensional dissipation rate ⟨Cε(ti)⟩ (ti is the local time) both in the static

K. Nakamura, T. Matsushima, Y. Zheng, K. Nagata, and T. Watanabe Large- and small-scale characteristics in a temporally developing shearless turbulent mixing layer Physics of Fluids, 34 115117 2022 This article may be found at  https://doi.org/10.1063/5.0121047 . The PDF is also available  here .    This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.  Abstract Direct numerical simulation of a temporally developing shearless turbulent mixing layer is performed. Two quasi-homogeneous isotropic turbulent (HIT) regions with different turbulent kinetic energies (TKEs) and a mixing-layer region temporally develop. The small-scale properties are analyzed with the velocity gradient tensor. The statistics on the velocity variances show that the development of the mixing layer is divided into two stages. In the first stage, grid turbulence in the large-TKE region  has not fully developed and the center of the mixing laye

T. Watanabe, K. Nagata Energetics and vortex structures near small-scale shear layers in turbulence Physics of Fluids, 34 095114 2022 This article may be found at  https://doi.org/10.1063/5.0099959 . The PDF is also available  here .    This article may be downloaded for personal use only. Any other use requires prior permission of the author and AIP Publishing.  Abstract Vortices and kinetic energy distributions around small-scale shear layers are investigated with direct numerical simulations of isotropic turbulence. The shear layers are examined with the triple decomposition of a velocity gradient tensor. The shear layers subject to a biaxial strain appear near vortices with rotation, which induce energetic flow that contributes to the shear. A similar configuration of rotating motions near the shear layers is observed in a multi-scale random velocity field, which is free from the dynamics of turbulence. Therefore, the mechanism that sustains shearing motion is embedded as a kinemat

2次元翼周りの定常流れの解析 （2022年7月版） OpenFOAMのインストールについては こちら 2次元翼周りの定常流れの解析をするチュートリアルを動かします。通常のOpenFOAMの使い方と同じですが、Windowsクロスコンパイラ版だとparaFoamが使えないため、可視化の手順だけ異なります。チュートリアルについては以下のサイトが参考になります。https://www.xsim.info/articles/OpenFOAM/Tutorials.html 可視化にはParaViewを使います。https://www.paraview.org/からダウンロードできます。 今回は非圧縮性流れの定常解析をするsimpleFoamを用います。 以下、 オレンジ背景の文字 はOpenFOAM上で入力するコマンドです。 1. OpenFOAMを起動する 2. チュートリアルのデータが保存されているディレクトリに移動 cd OpenFOAM/OpenFOAM-v2012/tutorials/  [Enter] ls  [Enter]       ファイル/ディレクトリ一覧を表示 チュートリアルのリストが表示される。各ディレクトリの中に解析手法の名前（**Foam）のディレクトリがあり、その中に様々な計算のチュートリアルが保存されている。ここでは、incompressible（非圧縮）内にあるsimpleFoam（非圧縮粘性流れの定常ソルバー）を使った2次元翼周りの流れのチュートリアルについて説明する。 3. チュートリアル用データを計算用ディレクトリRUNにコピー cp -r incompressible/simpleFoam/airFoil2D/ ~/RUN/   [Enter]      cp “A” “B” ： AをBにコピー       -r ：ディレクトリをコピーするためのオプション      ~/RUN ：起動時のディレクトリ”~/”の“RUN” 4. 計算用ディレクトリに移動して中身を確認 cd ~/RUN    [Enter] cd  airFoil2D   [Enter] 　チュートリアル用ディレクトリに移動 ls  [Enter]    中身の確認 5. 計算の実行（***Foam） simpleFoam [Enter]