Passive Blowing Strategy to Enhance Aerodynamic Performance and Noise of a Hollow-bladed Axial Fan: An Experimental Study

This research explores the efficacy of a passive control strategy designed to enhance the performance of an axial hollow fan. This investigation uses a dedicated experimental setup to evaluate various aspects of the fan's performance, including characteristics, efficiency, acoustic emissions, and flow topology. The control strategy involves introducing a portion of the main flow into the hollow fan through an upstream opening in the hub. Capitalizing on centrifugal forces, this air portion is injected into the fan's periphery via an axial slot at the rotating shroud ring. Additionally, to refine the previous strategy, a centrifugal fan is incorporated into the hub to assist in directing the flow toward the hollow blades and effectively overcoming losses. The study's findings reveal that implementing this control strategy broadens the fan's operating range and shifts its optimal operating point towards higher flow rates. This improvement is accompanied by a substantial increase in the fan's power density. Furthermore, a notable reduction in sound emissions of approximately 3 dB was recorded, especially when employing the centrifugal fan in the hub. This control strategy also significantly modifies the flow topology downstream of the fan, shifting it from an axial direction to a radial one.