J051041 Influence of Blade Number on Aerodynamic Noise of Half-ducted Propeller Fans

Flow fields in 2-blade and 4-blade half-ducted propeller fans for the outdoor units of air-conditioners were calculated with finite element method-based large eddy simulation (LES) with the aim of investigating what influence of blade number had on aerodynamic noise in this study. The aerodynamic noise of 2-blade propeller fan was smaller than that of the 4-blade by 5.9dB experimentally at an operating flow coefficient. As a result, we confirmed that the tip vortex (TV) had a great influence on half-ducted propeller fans. The TV trajectory and the blade pitch of the 2-blade propeller fan were longer than those of the 4-blade propeller fan. These suppressed the interaction between the TV and the adjacent blade, because the vorticity of the 2-blade propeller fan decayed along with the TV than that of the 4-blade propeller fan, and the minimum distance between TV and the adjacent blade of the 2-blade propeller fan was four times longer than that of the 4-blade propeller fan. The 2-blade propeller fan was therefore more silent than the 4-blade propeller fan.