On near-wall turbulence in minimal flow units

In the present work, direct numerical simulations are carried out for turbulent flows in a channel with minimal sizes in spanwise and streamwise directions required to get the so-called 'healthy' turbulence below a prescribed wall-normal height yh (i.e., yh+=100) at Reτ=1000, 2000 and 4000. It is found that, in the near-wall region (y < yh), the mean velocity profiles from the small flow domain agree well with those in the full-sized channel; the velocity fluctuations show good agreement with those of the full-sized simulation at scales smaller than the corresponding minimal channel size; turbulence statistics at different Reynolds numbers scale well in wall units, showing Reynolds number independence. All the results imply that the near-wall turbulence produced by minimal flow units reflect some universal properties of wall turbulence. Further comparison shows that the near-wall velocity fluctuations in the minimal channel are in good consensus with the universal signals in the predictive model for near-wall turbulence (Marusic et al., 2010a).