Broadband noise characteristics of fans with different blades under identical working conditions

Abstract

Small axis-flow fans are widely used for air cooling and ventilation systems. A common small axis-flow fan has an unshrouded rotor, structs or stator vanes and a round casing. The fans used in this work are designed based on isolated-airfoil blade design mode and simple radial equilibrium theory supplemented by three-dimensional flow simulations with steady flow. The noise radiated from the fan can be decomposed to discrete tones and broadband noise, which is mainly due to interaction between blades and structs or stators vanes and turbulence, respectively. Under the working conditions of the same pressure rise and volume flow rate, the noise spectra from different fans are analyzed. It is found that with the addition of the fan blade number, the concentration of the broadband sound energy gradually shifts from low frequency to high frequency. And the fewer the number of blades, the less the corresponding total broadband energy. Besides, the calculation results also show the fan with more blades can be absorbed more sound by the same sound absorption materials with the same volume. The findings are useful for improving the acoustic design of small axis-flow fans.