The controlled vortex design is a common criterion to distribute circulation along the blade span for high total pressure axial fan rotors when diameter and/or rotational speed limitations are imposed. In addition, industrial fans have to comply with Standards which impose high total efficiency.

Researchers involved in the field of fan blading fluid-dynamics showed that forward sweep of the profiles stacking line may give beneficial effects in controlled vortex design blading. However, the published literature is not always unanimous in quantifying these effects and still lacks of clearly outlined design criteria. The paper searches for design guidelines that increase the performance of a rotor-only tube axial fan featuring a constant swirl blade design without reduction in total efficiency. The original fan is experimentally tested and considered as base design for CFD models that were build to estimate the effect of design modifications. The study of the interaction between blade sweep angle, tip clearance and radial shift of the meridional flow across the rotor suggested a design procedure which increases fan total pressure of about 10% at design point and significantly extends the stable operation range while keeping similar values of total efficiency within the whole operation range.