Comparative studies have been carried out on two axial flow fan rotors of controlled
vortex design (CVD), at their design flowrate, in order to investigate the effects
of circumferential forward skew on blade aerodynamics. The studies were based on computational
fluid dynamics (CFD), validated on the basis of global performance and hot wire flow
field measurements. The computations indicated that the forward-skewed blade tip modifies
the rotor inlet condition along the entire span, due to its protrusion to the relative
inlet flow field. This leads to the rearrangement of spanwise blade load distribution,
increase of losses along the dominant part of span, and converts the prescribed spanwise
blade circulation distribution towards a free vortex flowpattern.Due to the above,
reduction in both total pressure rise and efficiency was established. By moderation
of the radial outward flowon the suction side, being especially significant for nonfree
vortex blading, forward sweep was found to be particularly useful for potential reduction
of near-tip loss in CVD rotors. Application of reliable CFD-based design systems was
recommended for systematic consideration and control of both load- and loss-modifying
effects due to nonradial blade stacking.
