ANALYSIS OF TONAL AND BROADBAND NOISE OF CENTRIFUGAL FAN USINGHYRID CAA METHOD WITH U- FRPM

Aerodynamic noise of rotating machines such as a centrifugal fan consists of tonal and broadband noises. The tonal noise component of a rotating machine is generated by steady pressure fluctuation on the structural surface in the rotating frame fixed the structure. The broadband noise component is produced by interaction between the rotating structure and turbulence in flow surrounding it. To predict flow field around a rotating machine, generally, Computation Fluid Dynamics (CFD) technique is used. The typical CFD techniques to solve the Reynolds-Averaged Navier-Stokes (RANS) equations can provide sufficient noise source information for the prediction of fan tonal noise, but it is difficult to apply the same technique for the prediction of the broadband noise because the RANS equations cannot resolve turbulence motion which is known to be broadband noise sources. In this study, UnsteadyFast Random Particle Mesh (U-FRPM) method is proposed for efficient prediction of broadband as well as tonal noise of a centrifugal fan unit by combining it with Hybrid Computational AeroAcoustics(H-CAA) method. The FRPM technique developed by Ewert can efficiently synthesize turbulence flow field from steady RANS solution. U-FRPM is proposed to synthesize random flow field from unsteady RANS solutions which are required for the accurate prediction of flow through the rotating centrifugal fans. H-CAA method combined with this U-FRPM technique is applied to analyze tonal and broadband noises of the centrifugal fan system. This also enables quantitative assessment of relative contributions to the tonal and broadband noise radiation of dominant noise source regions in the centrifugal fan unit.