Prediction and Mode Identification of Spike-stall in Centrifugal Compressor

In this work, unsteady full annular simulations of a centrifugal compressor with a volute were carried out. By an advanced dynamic mode decomposition method named compressed DMD, the dominant stall perturbation structure was extracted and analyzed firstly. Then, a twodimensional global stability analysis method based on the z-θ cylindrical surface at the impeller inlet is established to reveal the propagation behaviors of stall perturbation. The results demonstrate that the flow structure near stall can be decomposed into four patterns: stationary stall cell in the mean flow, perturbations associated with blade passing frequency and rotor frequency, periodic perturbations caused by compressor stable operation at stall inception, and oscillated stall cell in the origin place with the stall frequency of 40% RF. In the view of perturbation propagation features, it is mainly two propagations along the z-θ cylindrical surface. One is the reverse propagation to the upstream axially; the other is the secondary propagation to the blade leading edge with the effect of the main flow during the first propagation process. Two propagations form an unstable triangular region upstream of impeller.