Design Of Highly Loaded Axial Flow Fan And Analysis Of Aerodynamic Performance

Air cooling plays an important role in large power generators to remove theinside heating from electric-magnetic stator. The unit capacity of power generator isincreased and the rotating speed is limited, cooling air has to be supplied withmulti-stage axial flow fan which can provide more mass flow and higherpressure-rising capacity. Consequently, the length of main shaft is increased, whichaffects shaft stiffness and vibration characteristics. As the research objective, amulti-stage axial flow fan is redesigned in this paper. It is required to increase thepressure rise of single stage to reduce the stage number. Keeping the size of fan andoverall performance same, four-stage fan is redesigned into three stages. The mainwork of this paper is as follows:Firstly, the new straight rotor is designed instead of the original twisted rotor.The new single-stage fan and the original one are simulated with the softwareFine/Turbo for comparing their aerodynamic performance. The results show that themass flow and pressure rise remain the same, which meet the design requirement,when the straight blades replace the twisted blades.Secondly, the highly loaded blade airfoil is designed. The speed triangle at midspan is redesigned. The camber line of the highly loaded profile is arc and thecamber is increased. Highly loaded airfoil is constructed by imposing the thicknessdistribution of NACA65-010series upon the designated camber line. The analysis ofsingle-stage aerodynamic performance indicates that the static pressure rise fromhighly loaded fan increases by19percent with the efficiency decreases by0.3percent in value at the design operation.Thirdly, the bowed blade to control radial pressure gradient is applied toalleviate the radial flow and improve the aerodynamic performance of the highlyloaded fan. The results show that the bowed rotor effectively controls thedevelopment of boundary layer and suppress the low momentum fluids flowseparation in the hub region. At the design operation, the pressure rise has increasedby33percent and the efficiency also increases by1.14percent in the highly loadedfan of bowed rotor.Finally, the four-stage axial flow fan and the three-stage axial flow fan withhighly loaded bowed rotor are simulated. The results show that the pressure rise of three-stage achieves78.6percent pressure rise of the four-stage fan with little loss ofefficiency. Optimal operating point is changed towards large flow rates.The work of this paper shows that it is successful to increase the pressure rise ofa single-stage axial flow fan with a high cambered and bowed blade. However, dueto the interstage mis-matching, the performance of subsequent stage does not meetthe single-stage fan standard and the integrative performance of the multi-stage axialflow fan is declined.