Abstract
The ring fan is a propeller fan by an axial-flow impeller that has a ring shape shroud on the blade tip side. In this study, the whole flow field of the ring fan is simulated by a CFD code; the aerodynamic noise generated by the fan is predicted based on the wake characteristics. Moreover, the accuracy of the CFD code has been verified by comparing with the aerodynamic characteristics of the propeller fan of a current model. The aerodynamic characteristic of the ring fan by the CFD can represent the tendency of the measurement value qualitatively, however, the flow rate in the CFD becomes 30% lower than the actual measurement value. The main flow domain of the ring fan is formed 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 by the circumferential velocity. The sound pressure levels of the ring fan in the frequency band less than 200 Hz become larger than the propeller fan. According to the analysis on the wake characteristics, it clarified that (1) Karman vortex at the main flow domain is shedding in the frequency domain lower than 200 Hz, (2) the aerodynamic sound of the ring fan in the vortex shedding frequency becomes large because of an increase in the relative velocity and the velocity fluctuation.
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