Effects of Ribbed Blades on the Aerodynamic Performance of a Controlled Vortex Design Tube-Axial Fan

Leading-edge bumps, serrations, and trailing-edge indentations are commonly used to improve fan stall margin and mitigate noise emissions. However, these modifications often contribute to a reduction in aerodynamic performance at the design point. This paper aims to quantify the degree of confinement imposed on the meridional flow within the rotor passages by incorporating chordwise-aligned bumps, referred to here as ribs, on the blade surface. To this end, the aerodynamic performance of three fan configurations is investigated using validated CFD and analyzed in relation to local flow features. The baseline fan has a hub-to-tip ratio of 0.5 and an aerodynamic loading distribution characterized by a nearly constant exit swirl component. The second fan incorporates a spanwise-uniform distribution of ribs extending from the leading edge to the trailing edge across the entire blade surface. The third fan features the same ribs as the second but is designed to meet the same requirements as the baseline fan, with its design process neglecting the radial flow migration typically imposed by radial equilibrium in controlled vortex blade designs. The fans equipped with blades modified with five ribs matched the aerodynamic performance of the baseline fan, with a significant improvement observed at reduced flow rates and near-stall conditions.