Industrial fan noise control using flow obstructions

Fans are used in a lot of industrial processes and are sometimes a source of important noise for workers. The first aim of this study was to identify some problematic fans in Québec industries, for which the noise exposure exceeds the CSST (Comission de la santé et sécurité au travail) limit of 90 dBA for 8 h. We have focused on fans having a high tonal content, for which the Simple Silence technology can be applied, i.e., tonal fan noise control using obstructions in the flow. Two analytical models of the tonal noise radiated by these fans have been proposed: a free field model based on the Lowson model and an in-duct model based on the Goldstein model. The first free-field model has been applied to the control of the noise from a series of eight evaporator fans, having a strong blade passage frequency (BPF) tone at 90 Hz. These fans have been controlled in-situ, in a cold storage room, using trapezoidal obstructions in the downstream flow field of the fans. The second in-duct model has been applied to control the tonal noise from an in-duct air-extractor fan used in the underground gold mining galleries. Several obstructions have been tested in the upstream flow field.