Abstract
The stall warning method has been employed to predict the level of disturbances in active control systems. Significant advancements have been made by identifying the pre-stall disturbances. Revealing the characteristics of pre-stall disturbances under the distorted inflow is a key to realizing engineering applications. For this purpose, the stalling process and stall warning method were conducted in a two-stage transonic fan. Work on this project has concluded that the pre-stall disturbances initially arise in the region where the rotor exits the distorted region, diminish in the process of circumferential propagation, and ultimately disappear in the position where the rotor enters the distorted region. Due to the impact of circumferential secondary flow, the incidence is largest and the fluctuation of the tip leakage flow is strongest in the position where the rotor exits the distorted region. Consequently, the reduction in warning parameters can be first detected. In the pursuit of an effective stall warning system under inlet distortion, a novel warning index associated with the characteristic frequency band is proposed. This index, coupled with a variable threshold, enables stall warning at any circumferential position with only one transducer. The efficacy of this method is further validated under axial slot casing treatment boundary.
