Abstract
Active reducing the skin friction drag of vehicles (such as missiles, rockets, aircraft, high-speed train, submarines, etc.) during the navigation process can improve the respond speed effectively, save the energy consumption and increase the endurance time. As lots of active drag reduction methods were proposed for different applications, a review article is urgently needed to guide researchers to choose suitable methods for their pre-research. In this review, the generation mechanisms of skin friction drag under the action of disturbing the turbulent boundary layer are discussed, and the main active drag reduction methods are summarized. According to the actuation modes, we divided the active drag reduction methods into: drag reduction based on wall motion; drag reduction based on volume force control; drag reduction based on wall deformation and drag reduction based on micro vibration generated by piezoelectric actuator. The development status, drag reduction mechanisms, typical structures and drag reduction performance of each active drag reduction method are discussed and summarized in this work, which can provide preliminary research references for those who are engaged in the research of active wall drag reduction.
Highlights
Due to the impact of the oil crisis in the early 1970s, the drag reduction technology has developed gradually in recent decades
They found that when the wall oscillation waves propagated along the opposite direction of the flow, the skin friction drag always decreased, which was consistent with the results obtained by Quadrio et al Zhao et al [82] analyzed the drag reduction characteristics of turbulent pipe flow when creating oscillation waves propagated on the outer wall by Direct numerical simulation (DNS)
DRAG REDUCTION BASED ON WALL DEFORMATION The wall deformation drag reduction method is to use external actuators to make the wall deform which could interfere with the turbulent boundary layer, so as to achieve skin friction drag reduction [103]
Summary
Due to the impact of the oil crisis in the early 1970s, the drag reduction technology has developed gradually in recent decades. For objects moving in fluids (air, water, etc.), skin frictional drag is mainly generated in the region where turbulence occurs, and can be adjusted by controlling the characteristics of the near wall turbulent boundary layer. We mainly discuss the effective methods of controlling the coherent structure of the near wall turbulent boundary layer for reducing the skin frictional drag. Deng et al [22] achieved skin friction drag reduction by using the opposition active control method (wall blowing and suction), and studied the drag reduction characteristics when the method was applied in fluid with different Reynolds numbers. The mechanisms, characteristics, research status and application fields of active drag reduction technologies with different actuation modes are mainly discussed.
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