TABLE OF CONTENTS Repeated reference has been made to stall in the discussion of compressors, and a "stall line" has been included in the compressor and fan maps (this being defined by the limit in pressure ratio, for each compressor speed, beyond which the flow in the compressor breaks down in some way so as to make the system no longer operable). Some of the mechanisms for breakdown have been implied in the discussions of blade section stall, which may be thought to occur for a diffusion factor somewhat above 0.6, or casing stall, which may occur when the pressure coefficient demanded of the inter-blade passage near the tip exceeds a value on the order of 0.6-0.8. But this subject is of such critical importance to the performance of compressors in aircraft engines that it merits a thorough discussion. The presentation here will draw heavily on that of reference [5.25], but with emphasis on those aspects viewed as the most important for aircraft engines, and in a somewhat simplified form emphasizing the phenomena at the expense of quantitative treatment.
The simplest system that contains all the critical elements is shown schematically in figure 5.34. It consists of the compressor, a chamber into which the compressor discharges, and a nozzle or throttle through which the flow leaves the chamber. In application to the core compressor of an engine, the chamber represents the combustion chamber, while the throttle represents the first-stage turbine nozzles. But for purposes of the...
