Off-Design Performance of Supersonic Compressors With Fixed and Variable Geometry

Abstract

Regarding the extremely high pressure ratios of jet-engine compressors for the next decade, increasing interest belongs to the further development of supersonic compressors with supersonic relative flow at rotor inlet and supersonic absolute flow at stator inlet. In the past, different suitable design procedures for these components have been developed and tested successfully. However, there is a lack of information concerning the off-design performance of supersonic compressors. The present paper first systematically shows blading and flow path geometry of different experimentally investigated supersonic axial flow compressors. These investigations refer to combinations of characteristic rotors and stators with fixed and variable geometry. A comparison of these geometric data with the main characteristics of the flow pattern shows that, for the investigated stages, the three-dimensional passage geometry has an essential influence on the off-design performance. On the basis of this information semi-empirical models are established for a numerical description of the flow phenomena with predominant influence, as for example shock-, profile-, and endwall boundary layer losses and rotor-stator interactions. For the determination of the off-design performance, these models are incorporated into a streamline curvature calculation method. The computer model established is able to describe the off-design characteristics of the different investigated supersonic compressor stages in the most important operating range.