Surge and Stall Characteristics of Axial-Centrifugal Compressors: The Enhancement to Engine Stability

SUMMARY The characteristics of axial-centrifugal compressors in gas turbine engines that provide an enhanced tolerance to engine stall and surge are presented. The incipient, post-stall, and recovery behavior of axial-centrifugal compressors is described. Unique high-response measurements showing the pressure/flow characteristics of post-stall behavior are presented and the measurement techniques are discussed. Comparison of compressor stall and surge, with and without a centrifugal stage, shows the benefit of using axialcentrifugal technology in gas turbine engines. A discussion is presented on the importance and the technique of detecting the compressor stage that has the potential to initiate instability under highly-loaded conditions. Data are presented from both compressor rigs and engines. An explanation of how to distinguish the stalling stage prior to surge in a compressor is included. The effect of interstage bleed on the axial-centrifugal stage match in the engine environment is shown, along with the changes in surge initiation due to speed mismatch that can occur at high altitude conditions.