後流特性に基づくリングファンの空力騒音の予測

概要

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The ring fan is a propeller fan by an axial-flow impeller that has a ring shape shroud on the bladetip side. In this study, the whole flow field of the ring fan is simulated by a CFD code; theaerodynamic noise generated by the fan is predicted based on the wake characteristics. Moreover, theaccuracy of the CFD code has been verified by comparing with the aerodynamic characteristics ofthe propeller fan of a current model. The aerodynamic characteristics of the ring fan by the CFD canrepresent the tendency of the measurement value qualitatively, however, the flow rate in the CFDbecomes 30% lower than the actual measurement value. The main flow domain of the ring fan isformed at the tip side of the blade since the blade tip vortex is not formed at the blade tip side.Therefore, the relative velocity of the ring fan becomes fast due to the circumferential velocity. Thesound pressure levels of the ring fan in the frequency band less than 200 Hz become larger than thepropeller fan. According to the analysis on the wake characteristics, it clarified that (1) Karmanvortex at the main flow domain is shedding in the frequency domain lower than 200 Hz, (2) theaerodynamic sound of the ring fan on the vortex shedding frequency becomes large because of anincrease in the relative velocity and the velocity fluctuations.