Circumferential Grooves for a Modern Transonic Compressor: Aerodynamic Effects, Benefits and Limitations

Abstract

It has been shown in many cases that a notable aerodynamic stability enhancement can be achieved using circumferential grooves on transonic compressors. This advantage, however, often involves degradation in efficiency at design point conditions. In order to analyze the correlations between efficiency, surge margin and other flow quantities on the one hand and the geometric parameters related to circumferential grooves on the other, an automated multi objective geometry optimization of circumferential grooves for a transonic compressor has been performed. For the surge point determination an iterative approach was used to change the static back pressure until the numerical surge limit was determined with a sufficiently small uncertainty. As a result of the optimization two different types of grooves have been identified. The first type is comparatively small and located only little downstream the leading edge of the rotor. It is capable of increasing the surge margin, while only slightly decreasing efficiency. The second groove type is located more towards the trailing edge and significantly bigger in cross sectional size. It can improve the efficiency of the rotor, but at the same time blockage is generated. Combining the two groove types, also the effects combine, resulting in an increased surge margin and increased efficiency. Applying more than one groove of type one further increases the surge margin compared to a single groove, however the gain is limited. Important groove parameters of optimized grooves are further studied, regarding their sensitivity. The working principles and flow phenomena of the grooves increasing the surge margin are analyzed in detail.