Extraction and Reconstruction of Individual Vortex-Shedding Mode from Bistable Flow

摘要

For the flow around a circular cylinder under the synthetic-jet control, a bistable flow has been identified, in which the wake vortex sheds with the symmetric or antisymmetric mode. However, it is difficult to gain insight into the bistable flow due to the complexity with multiple dominant frequencies. Thus, it is aimed to reveal the underlying flow physics of the bistable flow by adopting advanced data-processing techniques. To obtain more accurate dynamic information, total dynamic mode decomposition was employed to extract dynamic modes, spectrum, and mode coefficients to describe the flow dynamics. It was found that the bistable flow contains dual dominant frequencies corresponding to the antisymmetric and symmetric vortex-shedding modes. The mode phi(1,c) for the control case approximates to the mode phi(1,n) for the natural case, representing the antisymmetric-shedding mode. However, the spatial distributions of the mode phi(2,c) are essentially different from those of the mode phi(1,c), representing the symmetric-shedding mode. The influence of the dominant modes phi(1,c) and phi(2,c) of the control case on the relevant physical components and flow structures was investigated in detail. The mode-competition process was illustrated to help understand the formation mechanism of the bistable flow. In particular, the total-dynamic-mode-decomposition reconstruction approach was adopted to recover the flow structures through superposing the zeroth mode and the different dominant modes. As a result, the individual vortex-shedding mode could be effectively isolated from the bistable flow by the total dynamic mode decomposition.