Numerical Optimization For A Three-stage Fan And Research Of Stall Flow And Reynolds Number Influence Of Two-dimensional Airfoils

The numerical optimization had been carried out to improve the performance of a three-stage fan. The process of optimization was executed under all three stages circumstances in order to reflect the interaction of rows. Numerical simulation on flow field of original blade indicated that there was a passage vortex in the corner near the hub of the 2nd stator which induced separation of suction root of the 2nd and 3rd stator. The method of curved blade and swept blade was applied to restrict the developmet of the passage vortex. Sweep and curving were realized by changing the circumferential or meridional stacking line and optimum parameters were searched by Design3D of NUMECA software.The results show that the 2nd stator using curved balde or the 3rd stator using swept blade all make the performance of fan improved. Analysis show that swept-curved blade row can exert influence on the others by changing the velocity density distribution along blade height. Swept blade can move not only the end-wall low energy fluid which is similar with the curved blade, but also the main flow fluid , so the swept blade's influence on velocity density distribution is larger than the curved blade. As the speed of rotation decreases, the effect of fluid migration of the curved blade is strengthened, whereas the swept blade is opposite. It is found that , the combination of curved and swept blade , which are all effective on improving the performance when used individually, can't get the double profit in performance.Supported by the 973 program, the thesis also study the numerical computing method of stall flow and Reynolds number influence of two-dimensional airfoils. k-ωSST turbulence model is combined with SA model to adapt to the numerical simulation of flow around airfoil in large attack angle range. The results show that trailing edge separated vortex, as the attack angle increases, is changed into alternately shedding separated vortex of leading and trailing edge which has great influence on pressure distribution of the airfoil lower surface. If the attack angle continues to increase, the vortex effect on pressure distribution of the airfoil lower surface will be decreased to the extreme minimum value and the time interval of separated vortex shedding increases. the change of Reynolds number mainly influences the attack angle range in which leading and trailing edge separated vortex alternately shed. The larger the Reynolds number, the smaller the lift and drag coefficient change caused by the change of Reynolds number.