Structure of rotating stall cells. Part 1: Absolute motion

Measurement and data processing techniques developed in order to define rotating stall characteristics are presented. Application of these techniques to experiments on an axial flow compressor yielded several conclusions on the structure of the stalled flow field as it is seen from the stationary frame of reference. Two qualitatively different types of rotating stall have been identified: small stall and big stall. Small stall results in a gradual drop in the performance of the compressor. It is characterized by many cells of small amplitude fluctuations of velocity and angle. It is linked to separation on the blades, but the flow continues to move through the rotor without significant reorganization. Big stall causes an abrupt drop in the performance. The velocity and angle variations are very big and the flow field inside the cells is reorganized in a three dimensional manner with the appearance of reverse flow in front of the rotor. Comparison with results of other investigations showed the similarity of the flow field inside the big cells in all cases.