Decoupling and reconstruction analysis in a transonic axial compressor using the dynamic mode decomposition method

Unsteady flow is highly related to flow loss and aerodynamic performance degradation in the axial compressor. In this paper, the dynamic mode decomposition method was used to investigate in-depth flow structures and related evolutionary mechanisms of the internal flow field. Four main flow structures were observed through flow field decoupling: the oscillation of the tip leakage vortex (TLV) region, the circumferential migration of the leakage-induced vortex (LIV), the axial migration of the rear part of the leakage vortex (RLV), and the oscillation of the leading edge vortex (LEV). All of those four structures indicated the presence of internal high disturbance regions. The reconstruction of the dominant mode flow field revealed that the unsteady evolutionary mechanism of the flow field mainly consisted of two components: the axial evolution of the RLV and the circumferential evolution of the LIV. It was further revealed that the axial evolution of the RLV was the primary reason for the formation of low-energy fluid mass within the passage; under the influence of the "leading edge overflow," the LIV eventually fused with the LEV. The blocking effect of the LEV led to the formation of a high oscillation region at the leading edge of the adjacent blade pressure surface, resulting in a synchronous moment between the emergence of the LIV and the LEV. The analysis of the two unsteady evolution mechanism components further supported TLV breakdown as the main cause of flow unsteadiness. This study laid the foundation for further accurate flow unsteadiness control.