Effect of circumferential grooving on the performance and flow mechanism of an axial flow fan with a large tip-clearance ratio

This study investigates an industrial axial flow fan with a large tip-clearance ratio of 1%. We use numerical simulations and experimental validation to examine how the number, axial location, and distribution of circumferential casing grooves affect aerodynamic performance under near-stall conditions. The results indicate that a single circumferential groove enlarges the low-velocity separation region within the tip clearance, intensifies turbulence, and aggravates flow blockage, thereby deteriorating fan performance. In contrast, a properly arranged multigroove configuration effectively suppresses tip leakage. The configuration involving a continuous circumferential groove structure significantly reduces blockage of the passage, which is associated with reverse-flow regions. Under near-stall conditions, this configuration increases static pressure by up to 15.7%, improves static pressure efficiency by 12%, and enhances the stall margin by 8.3%. These findings further reveal a zonal control mechanism of casing treatments in industrial axial flow fans with large tip-clearance ratios. Finally, grooves near the leading edge expand the radial clearance and promote the interaction and dissipation between reverse leakage flow and primary leakage flow. Conversely, grooves positioned near the trailing edge generate stable vortex structures that suppress the accumulation of reverse flow.