Flow bench and engine testing can be used to detect flow induced noise, but understanding the fundamental mechanisms of such noise generation is necessary for developing an effective design. This paper describes Computational Aero-Acoustic (CAA) analyses performed to obtain the broad-band and BPF noise sources
A computational aero-acoustics simulation on the aerodynamic noise generation of an automotive radiator fan assembly is carried out. Three-dimensional Computational Fluid Dynamics (CFD) simulation of the unsteady flow field was performed including the entire impeller and shroud to obtain the source of an audible broad-band flow noise between 2 to 4 kHz. Static pressure probes placed around the outer-periphery and at the center of the impeller inlet side and, at the shroud cavities to capture the noise sources. The static pressure at all probe locations were FFT (Fast Fourier Transform) processed and sound pressure level (SPL) was calculated.
The CAA simulations discussed in this paper identifies the SPL from the fan outer-periphery probes show the dominant source of blade passing frequency (BPF) and the broad-band noise. The BPF level is the strongest in fan outer-peripheral region because of large pressure fluctuations as a result of blade-passing. The broad-band noise on the other hand is the results of tip-leakage interactions with shroud surface and, vortex-vortex and vortex-surface interactions.
