Analysis of a severe rotating-stall phenomenon encountered in the fan core section of a three-shaft low bypass engine revealed interesting insight into the growth and circumferential extension of the stall cells immediately before surge of the high-pressure compressor was induced. The effect of a rotating distortion in contrast to the usually encountered stationary distortion is highlighted. The rotating distortion changes the time and hence the effectively felt distortion sector angle depending on a co- or contra-rotational arrangement of the distorting and the distorted compressor. The analysis shows that a contra-rotational arrangement provides a more stable and tolerant situation against that type of distortion. Analysis of the fan loading shows the static temperature rise coefficient to be the most descriptive for the fan rotor 1 hub section which initiated the rotating-stall mechanism.

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