Change of Stall Inception of Axial Compressor with Active Flow Control

Axial compressors are key components of aircraft engines, defining their operability. Active flow control is a powerful tool to optimize compressor stability, but the effect of these methods on the way the compressors run into stall remains unclear. In fact, previous works of the authors have shown that stall inception can be shifted from spike to modal type on the machine considered in this study. However, the transition from one mode to another is difficult to analyze with conventional methods. To explain the evolution of the stall process with an increasingly strong control action, the authors propose to study an experimental data set consisting of fast pressure transducers recordings measured during stall events with flow control. This work relies first on wavelet analysis but also proposes a new method inspired by system dynamic analysis to get a complementary view of the transition to stall for the controlled cases. The main finding is that spike instability disappears with only a very limited injected mass flow, as low as 0.4% of the main mass flow. Other interesting features are linked to the new method itself, providing a clear and computationally cheaper indicator of the stall process, and can be potentially investigated as stall warning method.