Influence of a Reflecting Plane on the Reference Sound Source of Multi-blade Fan

Abstract

The multi-blade fan is widely used for the reference sound source. Since the sound generated aerodynamically by it is considered to be caused by many dipole sources, behavior of the sound power and directivities of the sound effected by a reflecting plane is different from that of a monopole or a dipole source. For example, the sound power of the fan with the reflecting plane parrallel to the wheel shaft is within +1. 6, -1. 0dB as compared with that without the reflecting plane. In this paper, influence of the reflecting plane on the sound power and directivity characteristics of multi-blade fan is made clear by measurements on ILG181-12ZA and by calculation. The calculation is made on the assumption that the multi-blade fan consists of many dipole sources distributed randomly on the wheel and axes of these dipoles being normal to the wheel shaft. The results of measurements and calculations are in good agreement except for the case in the direction of the wheel shaft.