A numerical study on suppressing the logarithmic layer energy structures by a near-wall control approach to obtain drag reduction at relatively high Reynolds numbers

The energy consumption of an aircraft in flight is mainly due to the aerodynamic drag force. The viscous drag, which is directly related to the friction drag, is responsible for almost half of the total drag. At high Reynolds numbers, the energy-containing structures in the logarithmic region (log-layer) are highly effective in enhancing near-wall turbulence. In the present study, a near-wall control approach is applied and explored to a turbulent channel flow. The control approach suppresses the positive wall-normal fluctuations near the wall to manipulate the interplay between the log-layer and near-wall turbulent structures. Amplitude modulation analysis is employed to relate the drag reduction with the absence of energy structures in the logarithmic layer for the control applied case. A channel flow at a frictional Reynolds number of Reτ=800 is used and the results are compared for the controlled and uncontrolled cases. The results show a significant drag reduction related to the absence of large-scale (LS) motions in the log-layer region.