Noise Generation Mechanism and Noise Reduction Design on Bi-Directional Radial Fan

C1 - Noise of Centrifugal Fans

Motor which rotates both clockwise and counterclockwise is used for traction motor of train, traction motor of the elevator and industrial motor. Bi-directional radial fan is applied to these motors so that the same cooling capability can be obtained whichever direction it rotate. Wind is inhaled from inner circumference side of the fan, and its direction is changed 90 degrees by a main plate. Finally, wind flows to the radial direction away from the fan blades. Because of such a complicated wind flow, as compared with an axial fan, noise of bi-drectional fan is loud in order to shear wind at a edge of a fan blade. Conventionally, the various-shaped fans were made and low noise fans were qualitatively determined in the experiment. Although Computational AeroAcoustics (CAA) is commonly used in recent years, it is not yet clear what kind of flow is the cause of noise increase of bi-directional radial fan concretely. In this research, the noise generating cause of the bi-directional radial fan was clarified by calculating flow correctly by Computational Fluid Dynamics(CFD). And, frequency and noise level were comfirmed by comparison of experiment and analysis. Moreover, the relation between airflow rate and noise was clarified, and the blade structure of reducing fan noise without lowering cooling capability was investigated. As a result, it turned out that the blade shapes of air inlet and outlet are related to noise increase. Based on the result, blade structure which controlled noise radiation was designed and the effect of noise reduction was comfirmed by measuring the sound. At the rotation speed up to 2000 rpm, it was confirmed that an about 2 to 3dB noise level can be reduced. This paper introduces the noise generation mechanism and presents low noise blade structure of the bi-directional radial fan.