Fouling detection in low speed fan using near-field diy sound pressure sensors

This work investigates the dynamics of rotating stall of a low speed axial fan in presence of fouling on the blades. Rotating stall is an aerodynamic issue of recognized importance in turbomachinery. The combination of rotating stall and presence of particles of dust and dirt from the surrounding environment, may lead to further issues in terms of performance, stall limit and blades life. In this paper the identification of the rotating stall pattern is carried out using time-resolved sound measurements in the far field region by means of a condenser microphone. The experimental tests are carried out with various geometries of fouling in order to evaluate the system ability to detect acoustically fouling and rotating stall. The results have been validated against state of the art techniques described in the literature. The acquired signals have been analysed using frequency domain analysis, and time domain analysis using a phase space reconstruction inspired technique. Both of the approaches demonstrate a modification of the stall dynamics in the low speed fan and allow the identification of diverse stall precursors and fouling presence.