Experimental Investigation of the Sound Emission of Skewed Axial Fans with Leading-Edge Serrations

Axial fans represent a major source of noise in technical systems. Based on investigations on airfoils, a promising measure for reducing the sound emission of such systems with axial fans is the application of leading-edge serrations to the fan blade. Hence in this study, the joint impact of fan-blade skew-as a commonly used noise-reduction approach-and leading-edge serrations on the sound emission of low-speed axial fans was investigated. Forward-, backward-, and unskewed fans with five different leading-edge modifications were used. For each fan, a reference configuration with straight leading edges and four configurations with sinusoidal leading-edge serrations (with two different amplitude values and two different wavelength values) were examined. The results show that, among the reference fans with unmodified leading edges, the forward-skewed fan had the lowest sound emission. The serrations applied to the unskewed fan lead to an increase in the efficiency and a decrease in the sound emission. When applied in combination with fan-blade skew, the serrated fans showed an even lower sound emission and a higher efficiency-even the forward-skewed fan, which already has a low sound emission without any leading-edge modifications. The highest sound reduction was achieved by applying the serrations with the smallest wavelength and the highest amplitude. The findings prove that even for low-noise fans with forward-skewed fan blades, a further sound reduction is possible with the use of leading-edge serrations.