Passive Air Injection Through Slots for Improving the Performance of a Hollow-Bladed Axial Fan: A Numerical Study

Currently, axial fans equipped with hollow blades are being increasingly adopted in various industrial applications owing to their lightweight design and low driving motor energy consumption. Consequently, there is a growing emphasis on enhancing their aerodynamic performances. In this study, we conducted a numerical investigation of the fan’s performance, aiming to improve it, using a passive air blowing control through 4 mm dimension slot with various positions, as this passive control technique is preferred for its feasibility and efficiency. This approach consists in exploiting the hollow nature of the fan and the centrifugal effect to direct a portion of the main flow from the geometrically modified hub to the tip clearance zone via the hollow blades. The results indicate a significant enhancement in the fan’s performance, with a 43% increase in aeraulic power for opened hub configuration, which is 11% higher than active control using the same fan geometry and operating conditions. Furthermore, incorporating a centrifugal fan into the hub increase the main flow by drawing in extra air, particularly at higher flow rates. This leads to a 12% increase in aeraulic power compared to the approach of opening the hub. Employing passive techniques can also enhance the fan’s performance and diminish the leakage flow that contributes to noise emissions and performance decreasing. This is evident in the substantial modifications observed in the overall flow topology around the fan.