Specific noise which consists of total pressure and fan noise is available to estimate the overall performance. In this study, a prediction theory of specific noise for a forward curved fan is proposed. The specific noises of the fans that have a different number of blades were discussed based on this theory. The predicted total pressure coefficient coincided well with the experiment. The fan noise of MF120 fan (120 blades) became 3.9dB smaller than MF40 fan (40 blades) because the relative velocity was reduced by the slip. It could be predicted quantitatively that the specific noise of MF120 fan was 2.4 dB lower than MF40 fan.

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