A review of turbulent skin-friction drag reduction by near-wall transverse forcing

The quest for reductions in fuel consumption and CO2 emissions transport has been a powerful driving force scientific research into methods that might underpin drag-reducing technologies variety of vehicular on roads, by rail, the air, or water. In civil aviation, skin-friction drag accounts around 50% total cruise conditions, thus being preferential target research. With laminar conditions excluded, skin friction is intimately linked to turbulence physics fluid layer closest skin. Thus, reduction focused depress activity near surface. most effective method doing so subject drag-producing flow near-wall an unsteady and/or spatially varying cross-flow component, either action transverse wall oscillations, embedding rotating discs surface plasma-producing electrodes accelerate direction. ideal drag-reduction margins order can be achieved. present article provides review response turbulent layers imposition wavy motion, encompassing experiments, simulation, analysis modelling. It covers issues such as margin actuation scenarios, underlying physical phenomena contribute interpretation origin reduction, dependence Reynolds number, passive control are inspired active control, forward look towards possible future practical realizations. authors hope this review, far extensive its kind subject, will judged useful foundation targeting friction-drag