Proper orthogonal decomposition analysis of boundary layer oscillating aspiration controlling separation flows in two-dimensional compressor cascades

Vortex structures of the separation flow fields in two-dimensional compressor cascades controlled by the boundary layer oscillating suction are numerically investigated. The proper orthogonal decomposition method is adopted to present the variation of characteristics owned by large-scale vortices. It is found that introducing unsteady excitations with proper frequencies into the steady aspiration results in a more effective control effect and the optimal oscillation frequency should be in line with the characteristic frequencies of the steady aspirated flow field. The separation flows can be decomposed in to several basic structures with the dominant one being in the manner of Karman vortex street regardless of the control method adopted. The boundary layer oscillating suction not only alleviates the separation by removing low-energy fluid, but also intensifies the harmonic flow element represented by proper orthogonal decomposition modes with others suppressed. The well-organized vortex shedding process could contribute to the loss reduction to some extent.