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

Industrial axial fans generally operate in non-uniform inflow 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 uniform inflow, two kinds of inflow non-uniformity are investigated, which are generated by different geometric obstructions. Detailed aerodynamic experimental results indicate that the steady circumferential flow distortion mainly affects the lower half of the intake duct, where a low-pressure region has been observed. Evaluating the far-field noise level, it is found that the non-uniform inflow induces a significant increase both in tonal noise and broadband noise, while the increase of tonal noise is related to the acoustic propagation character of fan. In summary, the sound pressure level (SPL) at blade passing frequency (BPF) for the tested fan stage can be increased up to 15 dB higher than the uniform flow condition, depending on the degree of inflow non-uniformity.