Reynolds stresses transport in a turbulent channel flow subjected to streamwise traveling waves

Reynolds stresses transport in a turbulent channel flow under streamwise traveling waves is analyzed in detail using direct numerical simulations to gain physical insights into the mechanism of drag reduction. Streamwise traveling waves are known to produce larger drag reduction margins compared to simple homogeneous wall oscillations. The aim of the current investigation is to identify and analyze the direct effects arising from streamwise traveling waves that leads to larger drag reduction margins compared to simple homogeneous wall oscillations. Several cases were considered, with amplitudes ranging from 0.15 to 1.25 (in outer units) at fixed angular frequency and wave number of 0.16 and 1.66 (in outer units), respectively, to yield drag reduction margins ranging from 26% to 58%, respectively. Streamwise traveling waves of large amplitudes were found to block the intercomponent energy transfer, resulting in shut off of the near-wall buffer layer dynamics. The analyses here suggest that the combined effect of loss of communication between low and high buffer layers with damping in the wall-normal Reynolds stress component is associated to the traveling wave effect and results in larger drag reduction margins.

Automated summary

This study analyzes the transport of Reynolds stresses in a turbulent channel flow under streamwise traveling waves using direct numerical simulations, aiming to gain insights into the mechanism of drag reduction. The findings reveal that streamwise traveling waves can lead to larger drag reduction margins compared to simple homogeneous wall oscillations. It is demonstrated that high-amplitude streamwise traveling waves block the intercomponent energy transfer, resulting in the shutdown of near-wall buffer layer dynamics and contributing to the larger drag reduction margins.