Modelling and dynamic mode analysis of compressor impeller spike-type stall with global stability approach

Flow instability associated with spike-stall restricts the development of advanced aero-engines with a high-speed centrifugal compressor. However, given the irregular structure of centrifugal compressor, few approaches can be applied to stability analysis. Considering the typical features of spike-stall, an implement of stability analysis method on the flow field of impeller inlet was proposed innovatively. Thus, in-depth comprehension of stall perturbation structure and accurate prediction of stall perturbation propagation can be obtained. In this work, an unsteady full annular simulation of a centrifugal compressor with a volute coupled with experimental validations was carried out by using the Reynolds averaged Navier–Stokes technique. Then, an advanced dynamic mode decomposition method named compressed DMD was employed to extract and analyze the dominant stall perturbation structure. Finally, considering the effects of eddy viscosity and molecular viscosity, a two-dimensional global stability analysis method based on the θ-z cylindrical surface at the impeller inlet is established to reveal the propagation behaviors of stall perturbation. The results indicate that the compressed DMD approach can capture low-frequency perturbation caused by stall accurately but not dependent on samplings. The flow structure near stall can be decomposed into the influenced mean flow, flow perturbation associated with rotor frequency and blade passing frequency with the frequencies of 1333 Hz and 9333 Hz, respectively, and stall perturbation with the frequency of 510 Hz. In the view of perturbation propagation features, it is mainly two propagations along the θ-z 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. Both propagation paths deflect to the rotation direction, and the deflection degree of the second propagation paths is larger than that of the first one, thus, a triangular instability region is formed. The researches not only provide a new thought for the application of stability analysis in the centrifugal compressor but also clarify the propagation characteristics of stall disturbance, which lays a foundation for accurate flow control.