Study of Blade Tip Vortex and Aerodynamic Noise of a Propeller Fan (Influence of Axial-direction Relative Position)

The objective of this study is to clarify the relationship between the tip vortex and aerodynamic noise of an open type propeller fan operating at the vicinity of the maximum efficiency point. The influence of the internal flow on the aerodynamic noise is discussed with taking account of the axial direction relative position. In this experiment, when the relative position is 20 mm, the periodical noise at 200 Hz which is the low frequency side than that of the blade passing frequency became large. The periodical noise became the one of the important factors for increasing the fan noise by 5dB. The periodical noise was generated by the interaction between the tip vortex and the partition of the fan. It was clarified that when the wake formed the flow regime of the high specific speed type impeller the blade tip vortex noise was generated