Effect of upstream rotor vortical disturbances on the time-averaged performance of axial compressor stators: Part 1 - Framework of technical approachand wake-stator blade interactions

In a two-part paper key computed results from a set of first-of-a-kind nume rical simulations on the unsteady interaction of axial compressor stators w ith upstream rotor wakes and tip leakage vortices are employed to elucidate their impact on the time-averaged performance of the stator. Detailed inte rrogation of the computed flowfield showed that for both wakes and tip leak age vortices, the impact of these mechanisms can be described on the same p hysical basis. Specifically there are two generic mechanisms with significa nt influence on performance: reversible recovery of the energy in the wakes /tip vortices (beneficial) and the associated nontransitional boundary laye r response (detrimental). In the presence of flow unsteadiness associated w ith rotor wakes and tip vortices, the efficiency of the stator under consid eration is higher than that obtained using a mixed-out steady flow approxim ation. The effects of tip vortices and wakes are of comparable importance. The impact of stator interaction with upstream wakes and vortices depends o n the following parameters: axial spacing, loading and the frequency of wak e fluctuations in the rotor frame. At reduced spacing, this impact becomes significant. The most important aspect of the tip vortex is the relative ve locity defect and the associated relative total pressure defect, which is p erceived by the stator in the same manner as a wake. In Part 1, the focus w ill be on the framework of technical approach, and the interaction of stare r with the moving upstream rotor wakes.