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Changes in turbulent dissipation in a channel flow with oscillating walls

This paper presents key results of a novel approach to study the physical mechanism of active turbulent drag reduction. The work originated from a long-lasting international collaboration involving researchers in Japan, Italy, and France. Prior to this work, it was unclear how a sustained turbulent drag reduction could be achieved by large-scale sinusoidal wall oscillations along the spanwise direction, despite wide numerical and experimental attempts. For the first time, this research proves how the oscillating wall acts on the vorticity lines to transiently increase the turbulent dissipation, which results in a lower turbulent kinetic energy and therefore drag reduction.