渡邉 智昭 (Tomoaki Watanabe)

The response of small-scale shear layers to perturbations in turbulence T. Watanabe and K. Nagata 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. Fur...

The response of small-scale shear layers to perturbations in turbulence Authors: T. Watanabe and K. Nagata Journal of Fluid Mechanics, Vol. 963, A31 (2023) 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. Furthermore, DNS are carried out for decaying turbulence initialised by the a...

P. D. Tung, T. Watanabe, K. Nagata LES investigation of a piston-driven synthetic jet actuator with multiple orifices CFD Letters, 16 1998-2009 2023 The PDF is available  here .  This article may be found at https://doi.org/10.37934/cfdl.16.1.150170. Abstract A piston-driven synthetic jet actuator has the potential for application in flow control and fundamental studies of turbulence, although the high-speed flow generated by this actuator is less investigated than a low-speed synthetic jet. The interaction of high-speed jets issued from a piston-driven synthetic jet actuator with multiple orifices is investigated with large eddy simulation (LES). The maximum jet Mach number is related to the maximum pressure inside the actuator regardless of the number of orifices. Temporal variations of the jet Mach number are almost identical for different cycles, and the jet formation in each cycle occurs under the same condi...

J. Xing, T. Watanabe, K. Nagata LES/Lagrangian-particle-simulation of a supersonic reactive turbulent planar jet   Journal of Fluids Engineering, 146 070902 2024 This article may be found at https://doi.org/10.1115/1.4065301. Accepted manuscript is available here.  This version is free to view and download for private research and study only.  日本語訳 (DeepL翻訳) 超音速反応性乱流平面噴流のLES/ラグランジアン粒子シミュレーション   GD

T. Mori, T. Watanabe, K. Nagata  Nearly homogeneous and isotropic turbulence generated by the interaction of supersonic jets  Experiments in Fluids, 65 947 2024 This article may be found at  https://doi.org/10.1007/s00348-024-03764-6  or on ResearchGate . Accepted manuscript is available  here .  This version is free to view and download for private research and study only.  Abstract This study...

J. Xing, T. Watanabe, K. Nagata Hybrid large eddy simulation and Lagrangian simulation of a compressible turbulent planar jet with a chemical reaction   International Journal for Numerical Methods in Fluids, 96 962-990 2024 This article may be found at  https://doi.org/10.1002/fld.5273 . Accepted manuscript is available here.  This is the accepted version of the article, which has been published in final form at https://doi.org/10.1002/fld.5273. This article may be used for non-commercial purposes in accordance with the Wiley Self-Archiving Policy  [http://www.wileyauthors.com/self-archiving]. Abstract Large eddy simulation (LES) coupled with Lagrangian particle simulation (LPS) is applied to investigate high-speed turbulent reacting flows. Here, LES solves a velocity field while LPS solves scalar transport equations with notional particles. Although LPS does not require sub-grid scale models for chemical source terms, mole...

R. Enoki, T. Watanabe, K. Nagata  Statistical properties of shear and non-shear velocity components in isotropic turbulence and turbulent jets Physical Review Fluids, 8 104602 2023 The PDF is available  here .  This article may be found at  https://doi.org/10.1103/PhysRevFluids.8.104602 . Abstract The triple decomposition of a velocity gradient tensor, which extracts local fluid motions of shear, rigid-body rotation, and irrotational strain, is extended to the decomposition of velocity vectors into shear and nonshear components. The present approach adapts the Biot-Savart law to reconstruct shear and nonshear velocities from the vorticity vectors of shear and rigid-body rotation, respectively. These velocities are related to the flows induced by small-scale shear layers or vortex tubes. The decomposed velocities are in...

M. Zecchetto, T. Watanabe, K. Nagata, C. B. da Silva   Turbulent/non-turbulent interfaces in equilibrium and non-equilibrium regions in the absence of mean shear International Journal of Heat and Fluid Flow, 103 109198 2023 This article may be found at  https://doi.org/10.1016/j.ijheatfluidflow.2023.109198 . 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 turbulent fronts evolving into a non-turbulent flow region in the absence of mean shear are generated for both classical (equilibrium) and non-equilibrium turbulence in order to study the characteristics of the turbulent/non-turbulent interface (TNTI) that separates regions of turbulent from non-turbulent (or irrotational) flow. The effects of the non-equilibrium can be observed in a number of statistics computed in the turbulent core region of the turbulent evolving fronts, such as ...

Y. Zheng, N. Koto, K. Nagata, T. Watanabe Unsteady dissipation scaling of grid turbulence in the near-field region Physics of Fluids, 35 095131 2023 This article may be found at  https://doi.org/10.1063/5.0161891 . Accepted manuscript is available here.  This version is free to view and download for private research and study only.  Abstract This paper investigates global (long-time-averaged) and local (short-time-averaged) statistics in the near-field region of static-grid turbulence through wind tunnel experiments. Measurements are performed in the region x/M<32 (where x is the streamwise distance from the grid and M is the mesh size of the grid) using hot-wire anemometry. Local statistics are calculated according to the methodology used in the previous time-dependent analysis [Zheng et al., “Unsteady dissipation scaling in static- and active-grid turbulence,” J. Fluid Mech. 956, A20 (2023)]. The global dimensionless dissipation rate Cε exhibits a power-law deca...

P. D. Tung, T. Watanabe, K. Nagata Large-eddy simulation of a flow generated by a piston-driven synthetic jet actuator CFD Letters, 16 1998-2009 2023 The PDF is available  here .  This article may be found at  https://doi.org/10.37934/cfdl.15.8.118 . Abstract We study the characteristics of a compressible flow generated by a piston-driven synthetic jet actuator by employing large-eddy simulation with OpenFOAM. The actuator consists of a piston and a cylinder with a square orifice on top and produces a compressible synthetic jet with the piston movement. Comparison with experimental data demonstrates that the numerical model constructed with OpenFOAM is useful to examine the performance of the actuator. As the piston frequency increases, the maximum pressure inside the cylinder increases while the minimum pressure decreases. The fluid temperature inside the cylinder also varies similarly to the pressure. The ...

A. Kusuhata, K. Tanaka, T. Watanabe, K. Nagata, A. Sasoh  Local geometry of a weak normal shock wave interacting with turbulence  Physics of Fluids, 35 086110 2023 Accepted manuscript is available  here .  This version is free to view and download for private research and study only.  This article may be found at  https://doi.org/10.1063/5.0158309 . Abstract The shock surface geometry is investigated with direct numerical simulations of a weak normal shock wave propagating in turbulence. The geometry is quantified with the principal curvatures of the surface. A large part of the surface has an approximately flat saddle shape, while elliptic concave and convex shapes with a large curvature intermittently appear on the shock surface. The pressure–dilatation correlation in the governing equation of pressure is investigated a...