On the structure of vorticity and near-wall partial enstrophy in fibrous drag-reduced turbulent channel flow

The structure of the vorticity field and the near-wall partial enstrophy in a fibrous drag-reduced channel flow at Reτ=180 with about 16% percentage drag reduction are studied and compared to the Newtonian flow by means of direct numerical simulation. The vorticity fluctuations as well as the distribution of the vorticity tilting angle is analyzed in detail. Moreover, the budget of near-wall partial enstrophy is investigated. It is found that in the drag-reduced flow, the tilting angle of vorticity reaches to the 45° more away from the wall than the Newtonian counterpart. Also, the decrease in the production term of vorticity fluctuations in the fibrous flow up to the wall distance z+=140 is attributed to the decrease in the streamwise vorticity fluctuations and the decrease in the correlation coefficient between the streamwise and wall-normal vorticity fluctuations.