Implementation of an Acoustic Stall Detection System using Near-field DIY Pressure Sensors

B3 - Measurement & Test

In this paper the authors suggest the use of an unconventional measurement method based on dynamic DIY transducers to measure the pressure instabilities in a low speed industrial axial fan, with the purpose of rotating stall detection. Rotating stall is an aerodynamic instability with a frequency typically half the rotor frequency, and in slow turbomachines such as industrial fans this frequency has a value even lower than 10 Hz.
The authors carried out the acoustic pressure measurements using a dynamic transducer and a piezoelectric sensor, in order to feature the former using the latter as a reference. The classical methods use piezoelectric sensors such as microphones in the far field and pressure transducers in the near field, collecting signals recorded in a wide frequency range. Other classes of sensors, such as electret microphones, may be not suited for pressure measurements, especially in the ultrasound region since their cut-off frequency is at least 20 Hz.
The authors comparea low cost and DIY technology and a high precision piezoelectric sensor already tested and widely described in literature. They implemented and set-up a measurement chain that is the basis of a stall warning system able to identify the rotating stall typical pattern. In this work the system is been test on a low speed axial fan. The results have been validated respect to the state of the art of the acoustic control techniques described in literature.
The signals acquired using the two technologies have been analysed though the frequency spectrum and the phase space reconstruction. The analysis aim was the detection of the distinguishing features of the investigated phenomenon. The patternacoustic recognition obtained through the phase space reconstruction for both the devices shows that the dynamic sensor is a good candidate solution for the rotating stall acoustic analysis.