Bleed-Induced Distortion in Axial Compressors

In this paper, the influence of non-uniform bleed extraction on the stability of an axial flow compressor is quantified. Non-uniformity can be caused by several geometric factors (for example, plenum chamber size or number of off-take ducts) and a range of configurations is examined experimentally in a single stage compressor. It is shown that non-uniform bleed leads to a circumferential distribution of flow coefficient and swirl angle at inlet to the downstream stage. The resultant distribution of rotor incidence causes stall to occur at a higher flow coefficient than if the same total bleed rate had been extracted uniformly around the circumference. The loss of operating range caused by the non-uniform inlet flow correlates with the peak sector-averaged bleed non-uniformity for all the bleed configurations tested. A connection is made between the analysis of non-uniform bleed extraction and the familiar “DC_θ” criterion used to characterize inlet total pressure distortion.