高频微秒脉冲放电控制激波/边界层干扰非定常性的实验研究

Experimental study on unsteadiness characteristics of shock wave/turbulent boundary layer interaction controlled by high-frequency microsecond pulse discharge

在马赫数2.5来流条件下,开展了高频微秒脉冲放电控制压缩折角激波/边界层干扰非定常性的风洞实验,放电位于压缩折角上游沿流向布局的6对电极之间,所选取的放电频率为14 kHz,接近于来流边界层的特征频率。采用高速纹影成像技术记录流场的动态变化,并基于纹影图像灰度值的时间序列采用平均、均方根、本征正交分解、动态模态分解、傅里叶变换等方法进行处理,对比研究有/无控制情形下激波/边界层干扰的非定常特性。研究发现,对于无控情形的基准流场,流动的低频特性表现为分离激波的振荡及边界层大尺度涡经过激波的脱落行为,中、高频特性表现为边界层小尺度涡与激波的相互作用;对于受控情形,来流边界层内的大涡尺度在放电作用下增大,大尺度涡与分离激波相互作用使得激波的振荡转变为稀疏压缩波的脉动,流经激波的边界层脉动更强,分离激波的低频振荡(10~300 Hz)有所改善。此时,流动的低频特性主要表现为边界层大尺度涡经过激波的脱落行为,而中、高频特性与基准流场相似。

Wind tunnel experiments are carried out to control a ramp induced shock wave/turbulent boundary layer interaction with high-frequency microsecond pulse discharge in a Mach 2.5 supersonic flow.The discharge is generated between 6 pairs of electrodes arranged in the streamwise direction upstream of the ramp,and the discharge frequency f=14 kHz is adopted,which is close to the characteristic frequency of the incoming boundary layer.High-speed schlieren imaging technology is used to record the dynamic flows.The recorded schlieren images are statistically processed by average,root-mean-square,proper orthogonal decomposition,dynamic mode decomposition,and Fourier transform methods based on their spatial gray values,and the unsteady characteristics of the shock wave/turbulent boundary layer interaction with and without control are compared and studied.The results show that for the baseline flow without control,the low-frequency characteristics are shown as the oscillation of the separation shock,as well as the shedding behavior of the large-scale eddies in the boundary layer flowing across the shock,and the middle and high-frequency characteristics are shown as the interaction between the small-scale eddies in the boundary layer and the shock.For the flow with control,the incoming boundary layer actuated by the discharge has eddies with an increased scale,which are interacting with the separation shock.As a result,the oscillation of the shock turns into the pulsation of multiple compression waves,the boundary layer flowing through the shock pulses more strongly,and the low-frequency oscillation(10-300 Hz)of the separation shock is alleviated.In this case,the low-frequency characteristic of the flow is mainly manifested as the shedding behaviors of the large-scale eddies in the boundary layer flowing across the shock,while the middle and high-frequency characteristics of the flow are still manifested as the vortex-wave interactions as those in the baseline flow.