Pressure Measurements in an Axial Compressor: from Design Operating Conditions to Rotating Stall Inception
The reduction of the environmental impact is nowadays the crucial challenge for the aeronautic industry. The following of a lower consumption of the vehicles has led to more compact and high loaded engines, increasing the internal flow unsteadiness and the occurrence of unstable phenomena, especially for compression stages. In this work the casing pressure characteristics in a single stage axial compressor both for normal-to-stall transient regime and for stalled conditions will be discussed. A special unsteady measurement window was designed, covering an entire rotor pitch, in the circumferential and in the axial extent, and allowing to solve pressure fields with high spatial resolution for several relative rotor/stator positions. A phase locked average technic was applied to obtain the pressure fields during normal and stalled operating conditions. The emergence of a spike-type pressure perturbation was captured during transient; the gradual alignment of the tip leakage vortex trajectory with the inlet rotor section was observed before the precursor appeared; this corresponds at one of the criteria for spike stall inception machines. An original way to observe the rotating stall phenomenon is proposed; the phase-locked technic used allowed reconstructing the average pressure field in the perturbation reference frame. The salient rotating stall pattern features will be described.