An investigation of the high alternating stresses in the blades of an axial-flow compressor

Abstract

A vibration investigation of the 1st, 2nd and 3rd stage stator blades of an axial-flow compressor gave high values of the alternating stresses of the order of 10,000 lb/sq in. On three runs excessive values of the alternating stress of 24,000, 27,500 and 48,000 lb/sq in. were obtained, and for these and forborne of the other maximathe incidence was estimated to equal the stalling incidence. There is excitation at all speeds of low orders showing dissimilar flow in different parts of the stage and this excitation increases in a critical manner at or near stalling incidence indicating a partial stall which is localised in parts of the stage. At greater incidence the flow deteriorates, the contrast between various parts of the stage is reduced, and the level of the alternating stress falls to a value slightly higher than that at incidences lower than the partial stall. This phenomenon occurs for critical operating conditions and is different from stalling flutter. Both phenomena could occur in the same compressor, the latter would be influenced by blade stiffness and could occur over wide ranges of operation provided the incidence and mass flow are greater than the lower boundaries.