The availability of high-quality numerical simulations, with Reynolds numbers which are now in the range of Reτ = 2000, and which will probably be extended to Reτ ≈ 4000 in the near future, have revitalized the study of turbulence near walls in the last decade. Simulations can now be used to study the dynamics of the buffer and of the lower logarithmic layers in some detail, and some of the results obtained in that way are reviewed here. Particular attention is paid to the reasons for the failure of the scaling of the turbulence intensities with uτ, which are traced to different causes in the buffer layer and in the outer flow. While in the buffer layer the cause seems to be the growing scale disparity between the near-wall and outer-flow contributions, it is shown that in the outer flow some spectral ranges scale with the centreline velocity. The generation of the largest scales of the streamwise velocity component in the logarithmic layer is also studied, and shown to be consistent with the formation of large-scale passive wakes of smaller individual ejections. The latter are related to attached clusters of vortices extending from the buffer region into the logarithmic layer.
The availability of high-quality numerical simulations, with Reynolds numbers which are now in the range of Reτ = 2000, and which will probably be extended to Reτ ≈ 4000 in the near future, have revitalized the study of turbulence near walls in the last decade. Simulations can now be used to study the dynamics of the buffer and of the lower logarithmic layers in some detail, and some of the results obtained in that way are reviewed here. Particular attention is paid to the reasons for the failure of the scaling of the turbulence intensities with uτ, which are traced to different causes in the buffer layer and in the outer flow. While in the buffer layer the cause seems to be the growing scale disparity between the near-wall and outer-flow contributions, it is shown that in the outer flow some spectral ranges scale with the centreline velocity. The generation of the largest scales of the streamwise velocity component in the logarithmic layer is also studied, and shown to be consistent with the formation of large-scale passive wakes of smaller individual ejections. The latter are related to attached clusters of vortices extending from the buffer region into the logarithmic layer. Read More
