Review of controlling flow separation over airfoils with periodic excitation

Active flow control is one of the most promising techniques that are employed in aeronautics and astronautics engineering in the 21st century. It will be a new degree of freedom of design for future air vehicles. Using this technique to control flow separation over airfoils is very meaningful for both fundamental research and applied research. Since periodic excitation is an efficient and convenient control method, it is significant to review the investigations on controlling flow separation over airfoils with periodic excitation. An evaluating parameter is introduced firstly, which is followed by some discussions about excitation frequency, intensity, location, and Reynolds number. Three aspects which are extracted from publications and should receive appropriate attention are presented. One is the evaluation criterion of efficiency, which can guide the design of forcing devices and operation modes. Another is the acoustic-dominated mode, which is observed in the high-frequency forcing cases. This mode may exacerbate flow separation. The third one is a phenomenon of drag anomaly that, in certain conditions, form drag is larger than total drag with excitation. At last, some recommendations for future research are made. This review is helpful for applications of flow separation control with periodic excitation. © 2020 Advances in Mechanics.