On drag reduction by spanwise wall oscillation in compressible turbulent channel flow

Abstract

In this chapter, we summarize our progress in the investigation of drag reduction (DR) by spanwise wall oscillation (SWO). Reliable direct numerical simulation (DNS) models have been established for compressible turbulent channel flow. A large amount of 39.3% drag reduction has been achieved for supersonic compressible flows. It is found that the compressible effect is modest with respect to the turbulent effect for the skin-fiction in compressible turbulent channel flows. The reduced DR is mainly because of the decreasing turbulent contribution, and the related small compressible term also slightly decreases with the increase Wm+. More DNS cases with different maximum wall velocities, oscillation periods, and flow Reynold numbers for compressible cases should be analyzed. The optimal combination with the highest drag reduction efficiency has significant importance on real applications, which deserves to be studied in detail to characterize the underlying mechanisms.