# A Study on the Stall Detection of an Axial Compressor through Pressure Analysis
## 1 Introduction  
With the expansion of the advanced aircraft envelope, aero propulsion has put forward higher requirements for the performance and stability of compressors. During aircraft super maneuver operation processes, compressor inlet conditions badly deteriorate. The worsening inlet airflow could shrink compressor surge margins and lead the compressor to rotating stall and surge. Meanwhile, compressor stall and surge are the main influencing factors that cause inherent aerodynamic instabilities in the compressor operational envelope [1,2]. A large number of studies have been carried out on the model of surge and rotational stall. Due to their complexity, it is difficult to establish an accurate real-time mathematical model. At present, most research is aimed at single compressor parts. In 1980s, the United States carried out computer simulation research of the whole turbofan engine surge, and published a research report [3,4]. Also, a NASA report pointed out that the T700 engine adopts active stability control to control the compressor, but the technical details are unknown [5]. [PERSON] identified the same problem [6,7]. As is well known, the compressor characteristics map of pressure ratio versus mass flow rate could reflect the compressor working performance. In other words, the inlet pressure and outlet pressure of the compressor could reflect compressor performance, to a certain extent. In order to investigate the relationship between the compressor pressure and performance, the study of the compressor requires massive numerical simulations and experiments [8,9]. As the pressures are easily observed or have been stored in other engine control sub-systems, pressures monitored at the inlet and outlet of the compressor are apparently the first choices for compressor performance analysis. In fact, inlet and outlet pressures on the compressor have played an important role in the engine fuel and nozzle throat area control system. However, the compressor's inlet pressure is easily disturbed by the inlet air conditions, such as compressor inlet distortion. As a result, the application of compressor potential performance needs more accurate estimations of compressor surge margins. Traditional compressor safety protections are restricted in the compressor potential performance application. Therefore, studies on the information at compressor blade tip region, including pressure, have been gradually emphasized. The references written by [PERSON], [PERSON] and [PERSON] [10; 11; 12] researched the working principal of compressor blade tip performance, which is difficult to apply in the engine compressor control system. The references written by [PERSON], [PERSON] and [PERSON] [13; 14; 15] studied the pressures at the compressor blade tip region, and found some interesting laws about the relationship between blade tip pressures and compressor surge margin. Nevertheless, compressor inlet distortion disturbances are neglected, which the papers written by [PERSON], [PERSON], [PERSON] and [PERSON] [16; 17; 18; 19] verified are significant impact factors in the compressor working performance. In this paper, the research is focused on estimating compressor stability through examining the compressor pressure signals under different compressor inlet aerodynamic conditions, including inlet distortion influences. A series of experiments were conducted to research the laws that affect how the compressor inherently works near stall state. The experiments approached the compressor from normal operating state to near stall state by controlling the flow of the compressor, while at the same time simulating the compressor's inlet distortion flow field. In order to discover the stability boundary of the compressor, the experiments measured the total pressure at the inlet and outlet of compressor under different speeds, and forced surge tests. In addition, the experiments also captured the compressor surge boundary under the condition of inlet distortion.