Effects of Blade Solidity and Aspect Ratio on a 0.5 Hub-to-Tip Ratio Tube-Axial Fan

Abstract Blade solidity and aspect ratio are the two geometrical parameters that bridge the preliminary sizing of the fan with the aerodynamic design of the blade. In a previous work, the present authors started investigating the topic with a comprehensive experimental campaign focused on 16 propeller fan design variants with a 0.2 hub-to-tip ratio, all designed for best efficiency operation at approximately 0.075 flow-rate coefficient and 0.008 pressure coefficient. As a further step of the research, this article investigates by experiments the influence of blade solidity and aspect ratio on the global aerodynamic performance of 0.5 hub-to-tip ratio tube-axial fan rotors designed for best efficiency operation at approximately the same flow-rate coefficient as the 0.2 hub-to-tip ratio fans studied in the previous research. The aim of the work is twofold: first, to extend the experimental data set of aerodynamic performance of comparable axial-flow industrial fan designs characterized by different blade solidity and aspect ratio; second, to investigate the role of the hub-to-tip ratio on the effects of the two design parameters. To this end, 18 additional fan design variants were designed and tested in accordance with the ISO-5801 standard and the collected data were compared to the data set made available by testing the original 16 design variants. The results confirm that the global aerodynamic performance of a fan design at best efficiency operation is primarily set by the hub-to-tip ratio. Solidity plays a role comparable to the hub-to-tip ratio only within the minimum-to-low solidity range, whereas the aspect ratio contributes to the definition of the fan efficiency—in designs with the high hub-to-tip ratio only—and the flow-rate coefficient at best efficiency operation—in designs with the low hub-to-tip ratio only.