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A compressible, nonlinear, quasi-three-dimensional, time dependent computational fluid model capable of capturing salient features of rotating stall and surge is demonstrated. The theoretical basis of the model is given and the numerical methods used to solve the resulting model equations are described. This model is based on solution of a single set of fully coupled equations, and the instability modes are arrived at in a mixed, fully dependent, manner. The full evolution, including precursor events, of rotating stall and surge appears to be captured. As illustration, the method is applied to two modern compression system stages.

In this paper, Multi-Resolution Modal Analyses (MRMA) on experimental data are presented to assess the stall-suppressant potential of air injection for an axi-centrifug al turbo-jet engine. Compact Harmonic Wavelets (CHW) are used in MRMA to analyze the rotating and axial modes at compressor Stage 1 and 2. Air injection tests on the engine were done with eight, almost equally spaced injectors in front of the compressor Stage 1. In stall/surge and air-injection open-loop tests, static pressure oscillations are recorded with eight fastresponse sensors at each compressor stage. The MRMA algorithm, applied to the sensed static-pressure oscillations, is capable of detecting pre-stall instabilities in the rotating and axial modes at more than 400 rotor revolutions before stall/surge. It also yields accurate estimates for the open-loop frequency response of the modes under air-injection. The results reveal a high coherence in modal responses to jetvalves actuation, high transfer gains, and reliable position tracking of the rotating modes. The frequency response of mode amplitudes are also reliably predictable by the MRMA methods. Effective stall suppression with air injection is feasible with either a linear scheme on the modal spatial Fourier coefficients (SFC) or on their amplitude. The MRMA results also suggest that, to effectively suppress stall in this engine it is necessary to control not only the rotating modes, but also the axial mode.