Experimental Study on Fan Aerodynamic Noise Variation Characteristics under Non-Proportional Variation Law

Abstract

This paper presents the noise characteristics of axial fans in the process of variable frequency adjustment, so as to clarify the basis of frequency adjustment and high-risk area division for practical purposes. In the aerodynamic performance experiment, 11 kinds of operating conditions (OC) were divided into 3 groups, and the air flow rate and power consumption were measured. At the same time, an aerodynamic noise experiment was carried out, and nine measuring points were selected to test the noise of the air inlet and shell. The data showed that the aerodynamic performance parameters have the characteristics of non-proportional law. The maximum ventilation coefficient of OC2, OC7, OC11 is 3.9%, and its noise always has a negative growth rate. Furthermore, the typical OC were selected from all experiments, and broadband noise and discrete noise analyses were performed. The results indicated that the fan noise of the changes under variable frequency adjustment may come from boundary layer noise and shedding noise. In addition, the fundamental frequency sound pressure level of discrete noise is the highest in the whole frequency band. At the high-speed condition, the contribution of higher harmonics to the fan overall noise increases, but the broadband noise is still the dominant noise. Finally, the noise rating was introduced, and the high-risk noise index was divided for the noise of the air inlet and the shell. It was found that the main noise variation index of typical OC mostly exceeded the high-risk noise index, and the main target frequency band of noise control is 250–4000 Hz.