Noise generated by low pressure axial flow fans, III: Effects of rotational frequency, blade thickness and outer blade profile

Abstract

In a previous paper [1], practical formulae which correlate the noise sound power of a low pressure axial flow fan to the design parameters of the impeller were derived analytically by introducing a simple model of the flow past the fan blade. The validity of these formulae was examined experimentally in respect to the effects of such parameters as number of blades and chord length on sound power [2]. In this report, the experimental results in respect to the effects of the fan rotational frequency and blade thickness at the trailing edge are described and these results are compared with the theory. The agreement of the theoretical and the experimental results is generally quite satisfactory. Finally, it is shown that the outer profile of the blade has considerable effects on both noise and aerodynamic characteristics of fans: that is impellers with blades swept forward are much superior to those with blades swept backward.