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

寻求减少燃油消耗和CO _2的方法运输中的排放一直是科学研究方法的强大动力，这些方法可能为公路，铁路，空中，水上或水上各种车辆运输的减阻技术提供基础。在民用航空中，在巡航条件下，皮肤摩擦阻力约占总阻力的50％，因此成为研究的优先目标。在排除层流条件的情况下，皮肤摩擦与最靠近皮肤的流体层中的湍流物理学密切相关。因此，减少阻力的研究集中在抑制表面附近湍流活动的方法上。最有效的方法是对近壁层进行主动控制，方法是使该层中的阻力产生流受到不稳定和/或空间变化的横流分量的影响，通过横向壁振荡的作用，将旋转圆盘嵌入表面或通过产生等离子体的电极在横向方向上加速近壁流体来实现。在理想条件下，可实现约50％的减阻裕度。本文对湍流近壁层对非定常波浪状横向运动的响应进行了详尽的研究综述。该综述涵盖了实验，仿真，分析和建模，主要是在通道流和边界层中。它涵盖了各种问题，例如在各种促动场景中的减阻裕度，以及对于各种促动参数而言，有助于解释减阻起源的潜在物理现象，减阻对雷诺数的依赖，受主动控制启发的被动控制方法以及对未来可能的研究和实际实现的前瞻性。作者希望本次综述是迄今为止针对该主题的最广泛的综述，它将被视为今后针对减少摩擦阻力的研究的有用基础。