Symmetrized dot pattern analysis for the unsteady vibration state in a Sirocco fan unit

Abstract

Abstract Sirocco fan units, also known as squirrel cage fans, are usually installed at the air conditioning systems of vehicles used in public transport. They must provide an accurate ventilation flow rate, with high efficiency and performance, but also without operative problems like underperforming, outages or breakdowns, which usually lead to compromise the comfort and quietness of the passengers. Due to their heavy duty, they are susceptible of such problems which finally cause poor ventilation, magnified in highly crowded situations, and important noise generation with uncomfortable vibrations. Periodic maintenance and regular monitoring are thus essential to control that the fan operative range ensures a correct operation. This paper deals with a series of working failures, typically encountered in industrial applications with Sirocco fans, like impeller unbalances, obstructed channels or blocked inlets. A database with vibration signals has been measured experimentally to obtain the forced response of the fan as a function of the flow rate for different troubled scenarios. Following, a Symmetrized Dot Pattern (SDP) technique, that transforms the temporal waveforms into polar maps, is employed to generate dot patterns which can discriminate between different working conditions and failures, allowing an easy visual identification. The final objective is to show the potentiality of this technique as a fault diagnosis methodology for typical squirrel cage fans, providing optimal parameters for its use. The results obtained are also compared with other diagnosis techniques, previously employed by the authors, for a complementary analysis of the vibrating condition of these centrifugal fans.