A nonlinear harmonic methodology is adopted to analyze interactions between adjacent stages in multi-stage compressors. Of particular interest are the effects of circumferential “aperiodic” distributions and the relative circumferential positioning (‘clocking’) of blades. The main feature of the present approach is that both the aperiodic and clocking effects are very efficiently included with circumferential “steady” harmonic disturbances. Consequently, a single run of the nonlinear harmonic solver using a single-passage domain can produce the whole annulus unsteady and aperiodic time-averaged flow field. In addition, performance variation at any clocking position can be obtained simply by post-processing the result. A case study is presented for a two-and-half-stage transonic compressor, and the present results show much stronger rotor-rotor interaction than stator-stator interaction. A mechanism leading to strong rotor-rotor interference seems to be the interaction between upstream rotor wakes and the downstream rotor passage shock waves. A rotor-rotor clocking study illustrates a qualitatively different loss variation with respect to clocking position in a transonic flow compared to that in a subsonic flow.
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