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.
This paper presents a simple but complete design method to obtain arbitrary vortex design tube-axial fans starting from fixed size and rotational speed. The method couples the preliminary design method previously suggested by the authors with an original revised version of well-known blade design methods taken from the literature. The aim of this work is to verify the effectiveness of the method in obtaining high-efficiency industrial fans. To this end, the method has been applied to a 315 mm rotor-only tube-axial fan having the same size and rotational speed, and a slightly higher flow rate coefficient, as another prototype previously designed by the authors, which was demonstrated experimentally to noticeably increase the pressure coefficient of an actual 560 mm industrial fan. In contrast, no constraints are imposed on the hub-to-tip ratio and pressure coefficient. The new design features a hub-to-tip ratio equal to 0.28 and radially stacked blades with aerodynamic load distribution corresponding to a roughly constant swirl at rotor exit. The ISO-5801 experimental tests showed fan efficiency equal to 0.68, which is 6% higher than that of the previous prototype. The pressure coefficient is lower, but still 12% higher than that of the benchmark 560 mm industrial fan.
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