2410 小弦節比翼列ディフューザを有する遠心送風機の騒音特性(S41-1 流体機械に関連した複雑内部流動の解析と計測(圧縮機・ファン),S41 流体機械に関連した複雑内部流動の解析と計測)  [in Japanese] 2410 Noise Characteristics of Centrifugal Blower with Low Solidity Cascade Diffuser  [in Japanese]

In the present study, the diffuser performance and the sound pressure level were measured in a low specific type centrifugal blower with/without a low solidity cascade diffuser (LSD), and the frequency spectra were compared between the LSD and the vaneless diffuser. The flow behavior was also simulated _using a Navier-Stokes solver by ANSYS-CFX. The higher pressure rise in the diffuser was obtained by means of the LSD at the flow rates smaller than the design flow rate, however, noise level increased significantly at the off-design condition, comparing with the case of vaneless diffuser. It is found that the overall sound pressure level does not always increase by means of the LSD in the low flow rate range where the reverse flow induced by the LSD does not reach the impeller exit, on the other hand, the noise increases significantly when the reverse flow comes to the impeller exit. This noise increase is based on the broadband noise due to interaction between the reverse flow and the impeller, and also the discrete frequency noise defined by the cross product of the rotational speed of the impeller and the number of LSD.