A closed-loop control circuit comprising of hot wire sensitive filament sensor

microprogrammed control unit (MCU) controller and double piezoelectric vibrators was designed to realize the coherent structure’s drag reduction in turbulent boundary layer under closed-loop active control. Asynchronous vibration of the spanwise piezoelectric vibrators on the wall was adopted. By inputting three different vibration frequencies to the piezoelectric vibrator

the maximum drag reduction efficiency of 16.03% at 160 Hz was acquired. The vibration of the piezoelectric oscillator made the turbulent kinetic energy concentrate around the maximal energy and modulated the coherent structure

which changed the structure of the turbulent boundary layer near the wall. When the vibration frequency of piezoelectric vibrator was close to the characteristic frequencies of coherent structures

the disturbance of piezoelectric vibrator exerted the most significant burst influence on coherent structures

and the drag reduction efficiency reached the maximum. Closed-loop control saved about 75% energy input and achieved a comparable control effect as open-loop control. Under the controlled condition with added condition detection

the time period of the conditional phase average waveform became shorter. The disturbance of piezoelectric oscillator was used to modulate streamwise vortex

thus the wall friction resistance was reduced

and the drag reduction effect was obtained.