Discovery, interpretation, and model-based judgment of a hidden operating condition during the process from compressor stall to surge induced by inlet distortion

This paper mainly focuses on the research of a hidden operating condition that exists during the compressor's stall and surge processes caused by inlet distortion. It also delves into the mechanism of this operating condition and finally makes a judgment on the compressor's operating condition based on the model. Relying on the high-speed axial compressor test platform of Northwestern Polytechnical University, inlet distortion is realized by circumferentially covering the occlude, and the characteristic parameters are measured via tail cone throttling. The research reveals that inlet distortion causes a new hidden condition in the compressor between stall and surge, named "secondary stall condition", which is characterized by its occurrence after stall and prior to surge, with a distinct frequency signature. Meanwhile, this paper uses a full-channel grid for numerical calculation, adopts specific calculation methods and turbulence models, sets reasonable boundary conditions, and simulates the secondary stall condition based on conditions such as 60° total pressure inlet distortion. The validity of the results is ensured by comparing them with the experimental data. The findings indicate that the fluid flow and vortex structure behind the distortion region affect the compressor performance, and the fluid situation in the channel under the secondary stall condition is more complex and has greater harm. At the same time, a compressor stability model based on pressure signals is constructed. Taking the inlet distortion tensor, pressure pulsation frequency ratio, etc., as the key parameters, the support vector machine (SVM) and radial basis function (RBF) kernel are selected. After being trained with experimental data, it can accurately determine the operating state of the compressor with an accuracy rate of 99.93 %. This provides a solid guarantee for the safe and stable operation of the compressor.