Guard grill impact on aerodynamic integral and acoustic characteristics of an axial fan

This paper presents the impact of a guard grill design on the aerodynamic integral characteristic, the spectrum of sound pressure level and total sound power level. Four characteristic operating points of axial fans with a standard guard grill, with an optimized guard grill and without a guard grill were studied. Measurement results of the local outflow velocity vector of the axial fan without a guard grill at an optimal operating point were used to model the optimized guard grill contour. The guard grill of axial fan has a significant impact on the aerodynamic integral characteristic in the mostly used operating region. The influence of a guard grill is more characteristically reflected in the spectrum of the sound pressure levels via the vortex shedding frequency and consequently in the total sound power level of compared axial fans. Flow properties around grill wires were studied using an in-line cylinder cascade in the free velocity field at appropriate Reynolds numbers. Results are presented as power spectra of velocity fluctuations and spectra of sound pressure level and show good agreement with results of fan measurements.