采用DMD方法研究叶栅不同攻角的拟序结构

为分析平面叶栅分离流非定常拟序流动特征,对三个不同攻角下的叶栅进行了单通道的大涡模拟仿真,并采用动力模态分解（DMD）三个工况的流场结构进行了分析。DMD方法对包含复杂时空信息的叶栅分离流流场进行了解耦,剥离出了反映流场主要动力信息的模态,获得了其频率和与之对应的空间结构。并且通过DMD方法,将原本需要研究大量不同时刻的流场,转移到仅需要对少量模态的研究即可,实现了保留主要动力特征的低维近似。通过DMD分析表明:气流经过叶片前缘产生流动分离,形成不稳定的剪切涡结构,它和尾迹区脱落涡相互耦合,并形成新的拟序结构。随着攻角的增大,前缘剪切涡及其与尾迹涡的耦合也同时增强,流场变得更加复杂。 

Coherent structures of cascade under different attack angles with DMD method

In order to analyze the characteristics of coherent structures of unsteady flow in a cascade separation flow, the large eddy simulation of single channel cascade with three different attack angles was carried out. Moreover, dynamic mode decomposition was made to analyze the inherent structures of the three different operations. With DMD(dynamic mode decomposition) method, the complex temporal-spatial flow fields can be decoupled and the coherent structures of different frequencies and scales can be captured. Besides, the main frequencies and their structures can be got to reflect the main dynamic behavior. Moreover, with DMD method, thousands of different flow fields can be expressed by low dimension of only dozens of modes. With the application of DMD method, the results showed that instability shear vortex was generated by flow separation of the leading edge of the cascade, coupling with the shedding vortex in the wake zone, producing new coherent structure. When the attack angle became larger, the shear vortex and its interaction with shedding vortex were strengthened, making the flow field more complicated.