EFFECTS OF UPSTREAM WAKE PHASING ON TRANSONIC AXIAL COMPRESSOR PERFORMANCE

摘要

The effect on rotor work, of the phase of an upstream wake relative to the rotor, is examined computationally and analytically for a transonic blade row. There can be an important impact on time-mean performance when the time-dependent circulation of the shed vortices in the wake is phase-locked to the rotor position, as occurs when there is strong interaction between rotor static pressure field and upstream vanes. The rotor work is found to depend on the path of the wake vortices as they travel through the blade passage; for configurations examined, the calculated change in time-mean rotor work was approximately three percent. It is shown that the effect on work input can be analyzed in terms of the influence of the time-mean relative stagnation pressure nonuniformity associated with the unsteady (but phase-locked) wake vortex flow field, in that changes in vortex path alter the location of the nonuniformity relative to the rotor. Lower pressure rise and work input occurs when the rotor blade is embedded in a region of low time-mean relative stagnation pressure than when immersed in a region of high relative stagnation pressure. In addition to the work changes, which are an essentially two-dimensional effect, it is demonstrated that the location of the wake may affect the tip clearance flow, implying a potential impact on pressure rise capability and rotor stability limits. Model calculations are presented to give estimates of the magnitude and nature of this phenomenon.