Numerical Investigation Of Blade Geometry Effect On Performance And Dynamic Characteristics Of An Axial Flow Fan

With the increasing power plant unit capacity, the variable pitch axial flow fan has become one of the important auxiliaries of large thermal power unit with its advantages of high speed, large flow rate, and high efficiency. The power consumption of the fan accounts for 25~30 percent of the total consumption. The operation mode and economy of the fan are directly related to the economic operation of power plant. Therefore, it is of great significant to find measures to improve the fan performance and then reduce the total power consumption of the plant. Appropriate changes of the rotor blade tip structure can prevent the development of the leakage flow effectively and improve the axial fan performance. The blade tip structure has certain influence on aerodynamic performance, noise and blade dynamic characteristics of the axial flow fan.The performance and dynamic characteristics of the axial fan of type OB-84 under different grooved blade tips were simulated with Fluent and Ansys finite element dynamic analysis module. The flow field and loss distribution field both in and near the tip clearance under different blade tips were investigated. The tip leakage flow rate was also compared with that of the original fan. The double grooved blade tip structure obtains the best aerodynamic performance. Then the fan performance of the fan with a groove depth of 1.5mm, 3mm, and 6mm were discussed under the double grooved blade tip structure to seek the optimal groove depth. The equivalent stress, the deformation, each order natural frequency and vibration diagrams of the blade with various tip structures were analyzed to study the blade static structure and vibration characteristics.The results show that the length, morphology and location of the groove exert obvious influence on fan performance. The fan with grooved blade tips leads to a certain extent decline of full pressure but a distinct improvement in efficiency. The grooves perturb the flow and vortex fields which impede the development of the leakage flow and impair the mixing loss between the leakage flow and mainstream. In addition, case 4 namely the double grooved blade tip presents the best aerodynamic performance with an increasing efficiency by 1.05% at rated flow rate. The performance of the fan with double grooved blade tips varied significantly. 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 aerodynamic performance. The noise of the fan with double grooved blade tip is greatly improved, and it is increased by 14.88% under the designed condition, which will bring adverse effect to the normal operation of the fan. The static strength tests results of original blade and double grooved blade all meet the requirements of operation of the axial flow fan. Hence, the double grooved blade tip will not cause distortion failure and fracture failure of the blade. The characteristics of blade vibration reveal that each order natural frequency of double grooved blade is increased compared with the original blade and it is out of step with the blade passing frequency, so the resonance will not occur by adopting double grooved blade tip.