# A Study on the Stall Detection of an Axial Compressor through Pressure Analysis
## 2 Compressor Experiment Facilities  
The compressor experiments were conducted within the low speed compressor facilities of Nanjing University of Aeronautics and Astronautics. Different compressor working conditions were realized with the auxiliary of an air mass flow control valve. In the case of given compressor revolutions per minute (RPM), the compressor's geometric structure and the actuating mechanism of the control system are fixed during the experiments. As the airflow control valve turns down, working conditions get closer to the surge limit line for the compressor. Revolutions of 600 RPM, 800 RPM, and 1000 RPM are separately experimented under three inlet conditions. The inlet conditions are: without inlet distortion, with sole inlet distortion, and with symmetrical inlet distortion. Figure 1 shows the compressor experiment facility structure. It mainly contains four parts: the air inlet unit, the compressor body, the air outlet unit, and control devices. On the inner wall of the compressor, three sensors are separately arranged at the compressor inlet on the first level of the compressor rotor and outlet, which are both marked as \"9\" in Figure 1. These sensors are used to judge  
compressor stall and measure compressor pressure signals. In order to reduce the sensor installation volume, the sensors are embedded directly into the probe head. The signal measurement system in these experiments includes steady state measurement and dynamic measurement. The steady state measuring system includes a rotation speed measuring instrument, a pressure-measuring system, a steady pressure probe, and a signal storage processor, which is mainly used to get steady compressor pressure signals under different inlet conditions. The total of pressure-measuring points are set in the compressor inlet and outlet. The dynamic measuring system includes a dynamic pressure-measuring instrument, a dynamic pressure sensor, and a signal storage processor, which is mainly used to obtain a dynamic pressure signal and judge the compressor stall. The dynamic pressure-measuring points are set in the compressor inlet, outlet and the compressor first stage. In these experiments, the Programmable Quad Bridge Amplifier (PQBA) signal-acquisition module of the LMS signal acquisition system is adopted. The highest sampling frequency of the LMS dynamic signal acquisition system can get up to 200 kHz, and the digital analogue conversion accuracy is 16 bit. The dynamic pressure-measuring instruments adopted in this test are Copal Electronics Company P-2000 dynamic pressure sensors. In order to simulate the inlet distortion that happens in super maneuverability flight or other air inlet disturbance, a distortion-imitating device was installed closely behind the fairing. Two kinds of inlet distortion are simulated in these experiments: sole inlet distortion and symmetric inlet distortion. Figure 2 shows the device imitating sole inlet distortion, and Figure 3 shows the device imitating symmetrical inlet distortion. Although the sole inlet distortion and symmetrical inlet distortion both have an effect on inlet conditions, only the sole inlet distortion condition is considered in this article. Figure 1: Compressor experiment facility. Figure 2: Sole inlet distortion-imitating device. The inlet system includes a flared tube, fairing, an inlet duct, and a distortion simulator (including sole distortion and symmetric distortion simulators, which are mainly composed of skeleton, based mesh, and mesh, as shown in Figures 2 and 3). The exhaust devices include solute, the exhaust passage, throttle and the anechoic chamber. The power systems are control components and DC motor, whose rated power is 200 kw. The signal measurement system is constituted of sensors, signal processor and storage. The compressor has two-stage of axial flow, which includes a two-level stator and a two-level rotor. The main design parameters of the compressor are as follows. The compressor's outside diameter is 0.9 m, and its hub ratio is 0.6.