Design of cooling fan for noise reduction using CFD

Cooling fans are one of the main noise sources in pumps. Tonal noise produced at a multiple of the rotational frequency of the fan, the so-called blade passing frequency (BPF) and its higher harmonics generally dominate fan noise. Noise reduction is perhaps one of the most important parameter in pumps. Every noise reduction process starts with identification of noise sources and ranking of sound sources from the machinery. After the initial identification of typical noise sources, the noise levels are to be eliminated or reduced either by modifying noise producing equipment or redesigning. In the present work, a cooling fan system of a sea water pump is considered. CATIA software is used to model the system and computational fluid dynamics (CFD) techniques are implemented for the analysis. In the first phase, CFD analysis procedure is developed and implemented to the baseline fan to designate the sound levels at inlet and outlet. Experiments are conducted for the same baseline fan in anechoic chamber and noticed high frequencies. The numerical results obtained through CFD are corroborated with experimental results and they are found to be in good agreement. After validating the theoretical procedure, an attempt is made to redesign the existing fan with National Advisory Committee for Aeronautics (NACA) series by way of changing geometrical parameters to reduce noise levels. The noise levels are computed and compared with the baseline fan results. The redesign fan results indicate that the noise levels are low by 5-10dBs.