学術雑誌論文

学術雑誌論文

text

International Journal of Heat and Fluid Flow. 2020, 86, p. 108658

Hairpin vortices in the largest scale of turbulent boundary layers

Elsevier

英語

text

2020-12

https://doi.org/10.1016/j.ijheatfluidflow.2020.108658

We have conducted direct numerical simulations of a turbulent boundary layer for the momentum-thickness-based Reynolds number Reθ = 180–4600. To extract the largest-scale vortices, we coarse-grain the fluctuating velocity fields by using a Gaussian filter with the filter width comparable to the boundary layer thickness. Most of the largest-scale vortices identified by isosurfaces of the second invariant of the coarse-grained velocity gradient tensor are similar to coherent vortices observed in low-Reynolds-number regions, that is, hairpin vortices or quasi-streamwise vortices inclined to the wall. We also develop a percolation analysis to investigate the threshold-dependence of the isosurfaces and objectively identify the largest-scale hairpin vortices in terms of the coarse-grained vorticity, which leads to the quantitative evidence that they never disappear even in fully developed turbulent regions. Hence, we conclude that hairpin vortices exist in the largest-scale structures irrespective of the Reynolds number.

77681

Hairpin vortices in the largest scale of turbulent boundary layers

Elsevier

英語

2020-12

International Journal of Heat and Fluid Flow

86

108658

https://doi.org/10.1016/j.ijheatfluidflow.2020.108658

https://hdl.handle.net/11094/77681