A Numerical Study on Surge Degeneration (Stall Stagnation) and Recovery therefrom in Axial Flow Compressors

Phenomena of surge degenerations and recoveries therefrom, which are related with so-called stall stagnation problems, are studied on the basis of numerical-experimental results by one-dimensional surge simulations on a singlestage axial flow compressor and a five-stage one. The phenomena are observed to show some different tendencies depending on the number of stages and the relative location of the compressor in the flowpath. The mass flow amplitudes, as the measure of the surge sizes, show behaviors of either continuous decrease in the amplitudes or discontinuous ones in the degeneration process. The latter is seen in the five-stage compressor and the former in the single-stage one. The difference in the tendency appears to be influenced by the levels of the compressor pressure-ratios and by the relative compressor locations also. Recoveries from seriously degenerated surge situations are observed to be achieved by opening the exit valve widely. It suggests that the stall margins available for alleviating significantly the pressure loads are indispensable in the situation. In the sense, it could be said that the stall stagnation or non-recoverable stall is the phenomenon related intimately with the surge degeneration tendency in the compressor-flowpath system characteristics, deteriorated furthermore by operational factors on-site, such as insufficient stall margins and limited flexibilities of operational procedures.