Experimental study of a compact axial fan noise under non-uniform inflow

Industrial axial fans generally operate in non-uniform flow due to constrained installation conditions, which may have a significant impact on the fan noise radiation. In this paper, a systemic experimental investigation is presented with a focus on the aerodynamic behavior and far-field noise emission of a compact axial fan at subsonic conditions. Compared to the uniform flow, two different degrees of inlet distortion are examined, which are generated by different geometric obstructions. Detailed aerodynamic experimental results indicate that the steady circumferential flow distortion under investigation mainly affects the lower half of the intake duct, where a low-speed region has been observed. Evaluating the far-field noise level, it is found that the non-uniform inflow induces a significant increase in tonal noise, while exerting a negligible influence on broadband noise. It is noteworthy that the low-order blade passing frequency noise is particularly reinforced under these conditions. In summary, the sound pressure level for the tested fan stage can be up to 15 dB higher than the baseline, depending on the degree of inflow non-uniformity and BPF harmonic.