Implementation of an acoustic stall detection system using near-field DIY pressure sensors

In this paper, the use of DIY transducers is proposed to detect the pressure instabilities in a low-speed industrial axial fan. The authors aim is to detect rotating stall, a well-studied aerodynamic instability with a typical frequency that can be even lower than 10 Hz in low-speed industrial fans. Pressure transducers and piezoelectric sensors, such as microphones, in turbomachinery are used respectively in the near and far field as standard methods to perform time-resolved pressure measurements. Other classes of sensors, such as electret microphones, may be not suited for pressure measurements, especially in the ultrasound region because their cut-off frequency is about 20 Hz. In this study, the authors use a low-cost DIY technology, as alternative technology to stall detection, in comparison with a high precision piezoelectric sensor. The authors performed the pressure measurements using a dynamic transducer, a piezoresistive transducer, and a piezoelectric high sensitivity sensor that provides the measurement baseline. They implemented and set-up a measurement chain to identify the typical rotating stall pattern in low-speed axial fans. The results have been validated with respect to the state-of-the-art acoustic control techniques described in literature. The signals acquired using the two technologies are discussed using a combination of spectral and time-domain space reconstruction. The acoustic patterns obtained through the phase space reconstruction show that the DIY dynamic sensor is a good candidate solution for the rotating stall acoustic analysis.