Inflow effects on tonal noise of axial fan under system resistances

Abstract

An axial fan operates under system resistances owing to neighboring structures located in the front and back of the fan in the actual operating environment. In particular, the acoustic characteristics of the fan change depending on whether the upstream structures exist since they significantly affect the inflow distribution and inlet pressure. In this study, the measurements on three different shrouded fan configurations are conducted to investigate the inflow effects caused by the existence of the upstream structures on tonal noise radiated from the axial fans. An acoustic fan tester installed in an anechoic chamber facility is designed to simultaneously measure the performance and sound pressure levels of the shrouded fan configurations. In addition, the static pressure correction method is proposed to adjust for changing system resistance owing to the upstream structures. Noise levels radiated from both shrouded fan and shrouded fan with upstream structures are compared under the same system resistance conditions. The influences of upstream structures on discrete tonal noise are discussed in detail. Results show that the tonal noise levels associated with 1st to 4th BPF components of the shrouded fan with the upstream structures increase for all the operating conditions except for the high resistance conditions where the blade stall occurs.