Upstream Attenuation and Quasi-Steady Rotor Lift Fluctuations in Asymmetric Flows in Axial Compressors

This paper examines the quasi-steady lift variations experienced by a compressor rotor working in a circumferential inlet flow distortion. It is shown that for a given axial velocity distortion at the compressor face, the phase and magnitude of the lift fluctuations are strongly dependent not only on the geometry of the specified rotor, but on the total compressor configuration in which the rotor is operated. A simple numerical example is presented to illustrate this point. It is then demonstrated that the differences in the rotor lift fluctuation occur due to the upstream circumferential velocity component which is associated with the upstream attenuation of inlet velocity distortion. It is also pointed out that proper consideration of the circumferential component resioves an apparent discrepancy between two previous analyses of this problem. Finally, arguments are presented concerning the influence of the bound (blading) and downstream shed (wake) vorticity on the flow field upstream of the compressor. For the cases considered, it is shown that the induced velocity field associated with the upstream attenuation of inlet flow distortion is due equally to the bound and shed vorticity.