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