Numerical investigations on stator hub initiated stall in a single-stage transonic axial compressor

Abstract

A new kind of stall inception initiated from the stator hub region was recently identified by experiment in a transonic compressor. To further explore the mechanisms of the new stall inception, the detailed stall evolution is studied in this paper using full-annulus unsteady simulations. The simulations correctly predict several key characteristics observed in the previous experiments: (1) the stall precursor is initiated in the stator hub region; (2) the initial disturbance is axisymmetric; (3) asymmetric rotating disturbance is developed afterwards. The numerical results also illustrate that the stall evolution has two distinct phases: the part span stall and the global stall, which are associated with the axisymmetric and the asymmetric disturbances respectively. The axisymmetric disturbance is caused by the ring-shaped flow separation in the stator hub region, while the asymmetric disturbance is initiated by the breakdown of the symmetry of the ring-shaped separation. For both disturbances, the axial velocity waveforms are in anti-phase at the stator tip and hub region, so they have the 1st-order mode in the span-wise direction. Further discussions on the radial distribution of load indicate that the localized critical load is the key factor leading to the earlier occurrence of flow breakdown in the stator hub region.