双压电振子异步振动主动调制湍流边界层流向涡减阻

以热线敏感丝为感受器、单片机(MCU)为控制器、双压电振子为动作器构成闭环控制回路,实现闭环主动控制湍流边界层相干结构减阻。采用安装在壁面上的展向布置的双压电振子异步振动方式,通过对压电振子输入3种不同振动频率,得到160 Hz工况实现最大减阻率为16.03%。压电振子振动使得湍动能更大程度地集中在能量峰值周围,改变了湍流边界层近壁区的含能结构,对相干结构产生调制作用。压电振子振动频率与相干结构特征频率越接近,减阻效果越好。闭环控制中控制压电振子所需要的电能节省开环的75%,实现与开环控制相近的减阻效果。施加控制加入条件检测的条件相位平均波形时间周期略变短,以压电振子壁面扰动方式调制近壁流向涡,减小壁面摩擦阻力,获得减阻效果。 

Active modulation to streamwise vortex drag reduction of turbulent boundary layer by asynchronous vibration with double piezoelectric vibrator

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.