Circumferentially propagating characteristic dominated by unsteady tip leakage flow in axial flow compressors

Abstract

The unsteady tip leakage flow (UTLF) is experimentally studied to observe the circumferential propagation in axial flow compressors. The evolutionary process of the circumferential propagation is captured by utilizing a collection of time-resolved pressure transducers on the casing with circumferential and chord-wise spatial resolution. Results show that the circumferential propagation dominated by the UTLF exists and occurs only after the emergence of the UTLF in the throttling process. Since then, the propagating speed and the scale of disturbance gradually augment, until the transition to the propagating speed and scale of stall inception. The tip air injection is applied to further verify the aforementioned circumferential propagation. Two kinds of injected momentum ratios, namely, micro and macro injection adopted in single-rotor compressor, and two types of injected methods, i.e., external air source and self-recirculation applied in single-stage and three-stage compressor demonstrate that either micro injection with a small stall margin improvement (SMI) or macro injection with a large SMI, or the different injected types in single- and three-stage compressor, with the increasing stability-enhancing capability of tip air injection, the UTLF is effectively weakened, and the circumferentially propagating speed and the scale of the disturbance dominated by UTLF accordingly shows a decreasing trend. The above results provide guidance for understanding the relationship between the UTLF and stall inception in terms of circumferential propagation that can be used to predict the compressor stability.