Experimental Study of Blade Rigidity Effects on the Global and the Local Performances of a Thick Blades Axial-Flow Fan

An experimental investigation on the aerodynamic performances of thick blades axial-flow fans was carried out in this study. Two fans are considered, the first one is rotomoulded (in plastic) and the second one is milled (in aluminium). Both have exactly the same shape, except that the rotomoulded fan has hollow blades. They were designed from an existing fan (manufactured by plastic injection process) used in the cooling system of an automotive vehicle power unit. As far as shape is concerned, the only difference between the two first fans and the traditional injected fan is the blade thickness, whereas as far as rigidity is concerned, the only difference between the rotomoulded and the milled fans is the ability of the rotomoulded fan to be deformed easier than the milled fan. The aim of this study is to determine on the one hand the influence of the blade thickness and on the other hand the way the deformation of the hollow blades may affect the global and the local performances. The global performances of the fans were measured in a test bench designed according to the ISO 5801 standards. The curve of the aerodynamics characteristics (pressure head versus flow rate) and of the global efficiency are slightly lower for the roto-moulded fan. The wall pressure fluctuations were also investigated for three flow rates: one corresponding to the maximum efficiencies of both fans and the two others corresponding to an under-flow and an over-flow rate. The power spectral density (PSD) levels, are between six and nine times higher for the roto-moulded fan at nominal flow rate. At partial flow rate, however, the PSD levels are close for both fans.