多翼ファンの性能に及ぼすディフューザの影響

概要

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In order to clarify the influence of the diffuser on the characteristics of a forward curved fan, theinfluence of bare ratio and outlet angle on the characteristics of the fan was discussed by theexperiment of the actual fan and the numerical simulation. In the present paper, the mechanism of thediscrete frequency noise generated due to the separated flow of the diffuser is reported. The optimizedbare ratio was in the vicinity of 17 degrees. The fan separated inside of the diffuser generated thediscrete frequency noise due to interaction between the reversed flow from the diffuser and theimpeller rotating with the blade passing frequency. The efficient outlet angle existed within 10 degreesto 15 degree. The diffuser made by the outlet angle contributed for increasing the pressure ratio thanthat of the bare ratio. Furthermore, it was clarified that to restrain the separation in the diffuser iseffective for decreasing the fan noise.