Anslysis Circular Cylinder Flow Using Dynamic Mode and Proper Orthogonal Decomposition

The unsteady flow field of circular cylinder flow at Re =100 is numerically simulated. The stability of unstable equilibrium regime, transient regime and stable limit cycle regime which are in the process of Karman vortex street flow around a cylinder is analyzed by using DMD and POD methods respectively. The results show that: DMD method can accurately extract unstable mode and frequency in the unstable equilibrium regime and the transition regime, and extract shedding vortex modal, the high order harmonic mode and frequency in the stable limit cycle regime. DMD method not only can efficiently extract the main flow field structure mode and frequency, but also analyze the stability of the corresponding mode. Thus, it can get main characteristic of the dynamic system on the level of time and space. For POD method, a small number of modes contain most of the energy in the flow field. Based on FFT analysis mode amplitude, mode frequency can be obtained. However, sometimes there are modes whose multiple frequencies are coupled. POD method is unable to determine the stability of the mode extracted. So POD method gets the main space characteristic of dynamic system. In additional, DMD method has a broader applicability for flow type. Therefore, DMD method is more advantageous when stability of complex dynamics system need to be analyzed.