圆柱扰流非定常流动流场动力学模态分解

Dynamic Mode Decomposition of the Unsteady FlowFields Over a Circular Cylinder

为了解圆柱扰流中的大尺度有序运动特征,采用非定常数值仿真方法对圆柱扰流进行了研究,通过短时傅里叶变换方法对流场内典型监测点进行了时频分析,并引入DMD方法对非定常流场进行分析,获取了各阶流场模态的频率及分布特征。结果表明:DMD方法提取的模态频率与圆柱后方典型监测点时频分析得到的频率吻合较好,1阶模态表现为圆柱后方两侧形成的双列涡脱落特征,2阶模态表现为两侧涡团在圆柱正后方相互作用形成的类驻波特征。采用DMD分析与CFD计算相结合的方法,可以用于研究圆柱扰流的非定常流动特征。

The unsteady flow fields around a circular cylinder were calculated by the computational fluid dynamics(CFD)method.Fast fourier transform(FFT)was applied to analyze the pressure signals of typical monitor points behind the cylinder in the time-frequency domain.The dynamic mode decomposition(DMD)method was introduced to analyze the unsteady flow characteristics.The dominant flow modes and the corresponding frequencies were obtained.The results showed that the frequencies of the DMD modes matched well with the FFT frequencies of the monitor points.The first order dynamic mode showed the double-row vortex shedding on both sides behind the cylinder.The second dynamic mode showed the quasi-standing waves directly behind the cylinder caused by the interactions between the double-row vortex shedding.The method combined with DMD and CFD can be used to analyze the unsteady flow fields over a circular cylinder.