Analysis of rotor-rotor and stator-stator interferences in multi-stage turbomachines

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. [DOI: 10.1115/1.1508382]