Forward Blade Sweep Applied to Low-Speed Axial Fan Rotors of Controlled Vortex Design: An Overview

An overview is given on the research maintained by the author about the design aspects of three-dimensional blade passage flow in low-speed axial flow industrial fan rotors, affected by spanwise changing design blade circulation due to controlled vortex design (CVD), blade forward sweep (FSW), and their combination. It was pointed out that, comparing the CVD method to the free vortex design, the fluid in the blade suction side boundary layer has an increased inclination to migrate radially outward, increasing the near-tip blockage and loss. It was concluded that the benefit of FSW, in terms of moderating loss near the tip, can be better utilized for the rotors of the CVD, in comparison to the free vortex design. Compared to the free vortex design, the FSW applied to the blades of the CVD was found to also be especially beneficial in loss reduction away from the endwalls, via shortening the flow paths on the suction side—in any case being elongated by the radially outward flow due to CVD—and thus, reducing the effect of wall skin friction. The necessity of correcting the swept blades was pointed out for matching with the prescribed CVD circulation distribution.