Computational approach for predicting stall inception in multistage axial compressors

A new time-accurate computational approach for predicting stall inception due to long- and short-wavelength phenomena in multistage axial compressors is introduced. The computational approach uses a time-accurate single-blade-passage multi-blade-row strategy that includes many of the primary unsteady modes associated with the early symptoms of stall. High-frequency unsteadiness due to self-excited flow at scales of the blade passage and rotor tip clearance as well as low-frequency unsteadiness due to longitudinal system modes are included in this model. The new approach is demonstrated using the NASA Stage35 single-stage configuration with an extended up- and downstream duct. Nothing precludes the use of this model, however, for multistage and/or multipassage per blade-row configurations if the computer resources are available. The results from a series of time-accurate simulations near stall with this new approach are presented to demonstrate the self-excited unsteady pressure levels and frequencies that are computed to exist before, during, and just after stall. Results show that the self-excited flow has significant unsteady pressure amplitude and a spectrum containing both low-frequency system waves and high/moderate-frequency waves corresponding to the passage self-excited viscous flow in each blade row.