Abstract
The influence of different parameters in the design of multi-blade fan , such as the ratio inner diameter of outer diameter, D1/D2 , number of blades, Z, inclination angle,α, outlet angle,βd2 , and inlet angle,βd1 , were examined in order to study relation between the flow pattern and noise level. In the present report, we investigated the fan performance and the noise characteristic experimentally and compared with simplified two-dimensional CFD analysis. The flow pattern passing the blades under the different geometrical conditions was examined and discussed in terms of fan performance and noise level. The results shows that high efficiency and low noise were attained in range of D1/D2=0.8-0.84 , Z=35-45 , α=30°-40°, and βd2=155°-165°. For these conditions, it was found that the pressure loss and noise generation in the flow between blades were attributed to the separation of the flow which was induced by the circulated vortex at the suction side, reattachment of the separated flow, and shear flow at the trailing edge. It was also confirmed that a large inner to outer diameter ratio gives a defected performance and big noise generation because of no reattachment of the separated flow. Also, the increasing of blade number resulted in the increasing of high frequency noise due to the vortices generation in shear layer in spite of rectification of passing flow.
