Newsletter 2021.11 Index
Theme : "Mechanical Engineering Congress, 2021 Japan (MECJ-21)”
Workshop on Experimental Fluid Dynamics (EFD)
A lot of fans are used in our life. It is required to reduce the fan noise for our healthy life as much as high efficiency. The approach with computer simulation for fan noise is so difficult that the unsteady complicated flow phenomena are closely related to it. For many years, fan noise is basically analyzed with empirical and there are many important outcomes. It is introduced the approach that we have treated for reduce the fan noise. The fan noise has to be checked by spectrum distribution. Fan noise is consisted from two spectrum components, discrete frequency noise(DFN) and broad band noise(BBN). DFN is characterized by the same phase pressure fluctuation. The large correlation area exists with large pressure fluctuation. The tongue is the main noise source of DFN in centrifugal fan. Fig.1 shows that the largest fluctuation part is not main noise source but the large correlation part is important noise source. BBN is generated from unsteady flow with vortex. Flow simulation is effective tool even the steady flow simulation. Fig.2 shows the small centrifugal fan with small rectangular casing. There exists large vortex. It is forecasted to generate the BBN. It is set corner block to make weak the vortex. The noise level can be reduced with the block. This is the important effect of the flow simulation even the steady flow. The flow simulation and the many results of ages past are the important tools. The flow simulation is improved for the fan noise analysis and reduction as same as fan design for aero-performance. Even in the case, the empirical and theoretical performances are fundamental to fan noise reduction.
Fan noise, Noise characteristics, Noise source identification, Experimental methods
Fig. 1 Characteristics of discrete frequency noise in tongue; strong pressure fluctuation does not generate large noise, correlation area is closely relative to the noise.
Fig. 2 Flow simulation and noise characteristics of centrifugal fan with rectangular casing