Abstract: Adopting double grooved blade tip structure is one of the measures to improve the impeller performance by blocking the tip clearance leakage flow effectively. Basing on a variable pitch axial flow fan of OB-84 type, the performance of the fan with original blade tip and three double grooved blade tips with different groove depth are simulated by using numerical software FLUENT. Both the leakage flow field and loss distribution in and near the tip clearance are discussed. The vibration characteristics of original blade and double grooved blade tips are also checked with ANSYS finite element dynamic analysis module. The results reveal that double-grooved blade tip structure improves the distribution of leakage flow which hinders the development of leakage flow and thus impairs the mixing of the leakage flow and passage flow. The performance of the fan with double grooved blade tips varies significantly with a decrease in total pressure and an increase of efficiency to some extent under the designed operating condition. The impact of groove depth on fan performance is prominent in the vicinity of design flow rate while little influence in large flow rate. The double groove blade tip with a depth of 3mm obtains the optimal performance with an improvement of efficiency by 1.05 percent greater than the original fan at design condition and an improvement of surge margin. The characteristics of blade vibration show that each order natural frequency of double grooved blade is increased compared with the original blade and is out of step with the blade passing frequency, so the resonance will not occur by adopting double grooved blade tip.

Key words: aerodynamic performance, axial flow fan, double groove, groove depth, vibration characteristic