A New Practical Approach to the Design of Industrial Axial Fans: Part II — Forward-Swept Blades With Low Hub-to-Tip Ratio

The authors previously suggested a simple method to design forward-swept axial-flow rotors with blades having low hub-to-tip and high aspect ratios. This design method was demonstrated experimentally to increase the aeraulic performance of a small tube-axial fan having unswept blades and 0.4 hub-to-tip ratio, while maintaining the efficiency in the entire operation range. However, the method has not yet been assessed by experimental tests of lower hub-to-tip ratio designs where the strong three-dimensionality of the actual blade passage flow could compromise its validity. This assessment is the object of the present paper, which is aimed at examining the practical effectiveness of the forward-swept blade design method for low hub-to-tip ratio tube-axial fans. To this end, past results of the authors’ work are supported here by the design of a new 315mm forward-swept industrial fan derived from the 0.28 hub-to-tip ratio design presented in Part I of this paper. The ISO-5801 aerodynamic performance tests at blade Reynolds number of approximately 60,000 show that the method permits the design of forward-swept industrial fans capable of pressure coefficients in excess of 0.02 at aeraulic efficiency well above 60%, in a wide range of flow rate coefficients and blade positioning angles. Moreover, the method allows obtaining a pressure coefficient equal to 0.021 at 70% maximum efficiency, with an improvement of both the stall margin and stable operation pressure curve of the unswept design, if applied in combination with the complete fan design method presented in Part I of this paper.