Automatic stability control using tip air injection in a multi-stage axial flow compressor

Abstract

Automatic stability control is experimentally investigated using tip air injection in a multi-stage axial flow compressor. The warning signal is obtained according to the auto- and cross-correlation algorithm integrated in the digital signal processing controller for online monitoring wall pressure signal at different stages. It is used as a feedback signal to drive the discrete proportional jet valves. The control law depends on the stall margin improvement (SMI) versus injected momentum ratio relationship. The real-time detection algorithms based on the correlation theory are experimentally studied using a collection of pressure transducers installed symmetrically on the casing at different stages. The results reveal that because of the initial appearance of stall inception at the first stage, which induced a stall in all stages of the compressor, only the correlation coefficient detected at the first stage exhibits a decreasing trend in the throttling process. Moreover, only the tip air injection at the first stage can obtain a large SMI. Therefore, the correlation coefficient detected at the first stage is used as the feedback signal in the controller after verifying the influence of injected air on the correlation coefficient. Compared with steady injection, the proposed automatic stability control can save energy when the compressor is stable and provide protection to extend the stall margin when close to the stall point. With a nearly equal SMI as the steady injection (the maximum SMI is 20%), the energy of the active injected air is approximately one-fifth of the steady injection. This active control can fully consider the failure control such that when the control system is inoperative, the aero-engine continues safe operate under normal circumstances.