抄録
A unique feature of the cross flow fan is the eccentrically located vortex inside the impeller which is thought to result in the fan's high performance characteristics. The position and the circulation of the vortex are affected by the casing configuration of the fan. The vortex behavior has a large effect on the fan noise level, as well as on the fan performance. The experiments presented in the present study show that the reduction of the fan noise level is possible by installing annular bands around the ends of the impeller. Two sets of annular bands were used. In addition to the measurement of fan performance and noise levels, spectral (i.e., frequency) analysis of the acoustic signal was also undertaken. Further, flow measurements were undertaken to determine the vortex center location and to ascertain the mechanism of the observed noise reduction. Furthermore, a commercial 3-D flow analysis software package, SC/Tetra version 7 (CRADLE Co., Ltd.), was used to analyze the flow in the fan, confirming variation in the location of the vortex center with the small geometry changes and thus, indirectly, the effect of the annular bands on the fan noise level and performance.
