Frequency Characteristic of Pressure Fluctuation on Blade in Small Axial Flow Fan

Abstract

In recent years, the noise reduction of an axial flow type small fan for cooling electronic devices is required. In order to reduce the noise level of the fan, numerical simulations were conducted by using LES（Large Eddy Simulation）with DSM （Dynamic Smagorinsky Model）under different flow rate conditions. In this study, the tested fans have non-axisymmetric casing（Normal fan）．This paper described the relationship of the pressure fluctuation on the fan blade surfaces under different operating points. Operating points were design point（Q=0.0300 m³/s），maximum flow rate（Q=0.0376 m³/s）and half flow rate（Q=0.0194 m³/s）．The frequency characteristic of pressure fluctuation level was affected by motor stay and casing shape. In the fan having rectangular casing, pressure fluctuation on the blade surface had four times as high as rotational frequency because the four pressure changes occurred during one revolution. In the separation region at near the blade trailing edge, pressure fluctuation characteristic was independent with frequency.