The Differential Entropy Generation Rate as a Unified Measure for Both the Stability and Efficiency of an Axial Compressor

Abstract

Stability and efficiency are the two most important performance indicators of highly loaded aviation axial compressors; however, they often cannot be achieved simultaneously. As an effective means of stability expansion, casing treatment usually damages the peak efficiency. In this study, the differential entropy generation rate was used as a unified measure of stall margin and efficiency, so that both stability enhancement and efficiency improvement could be considered at the initial casing treatment design stage. NASA Rotor 67 was selected, and two single circumferential grooves at two different axial positions were applied, which served as a test case to check how entropy generation rates in the flow field vary with changes in peak efficiency and stall margin. The distribution of entropy generation and differential entropy generation rate were compared with that of the solid casing. The correlation between differential entropy generation rate and the peak efficiency was analyzed, and how the flow mechanism of casing treatments affects entropy generation was determined. Methods for measuring and comparing the impact of different casing treatments on peak efficiency are proposed. At the same time, the distributions of differential entropy generation rate in the near stall were explored, and the relationships between the differential entropy generation rate and the flow structures are detailed. A comparison of the influence of different casing treatment on stability is given with respect to the contours of the differential entropy generation rates. It is demonstrated that the differential entropy generation rate is a unified measure to balance the tradeoffs between the stability and the peak efficiency for different casing treatments for the same compressor.