Aerodynamic Design And Flow Structure Investigation Of A Transonic Axial-Flow Fan

The design of highly loaded compressors with high efficiency and stability plays an important role in the development of aircraft engines.The shock wave,boundary layer,tip leakage flow and their interaction have detrimental effects on adiabatic efficiency and stall margin.And high turning stator is designed to turn flow approximately to axial direction.The accumulation of low momentum fluid at stator hub corner is responsible for limited performance of the transonic fan.Therefore,it is necessary to study the effects of geometry on flow structure,and develop an aerodynamic design method that can control boundary layer,shock waves and various secondary flows to increase aerodynamic limits.Aerodynamic design,optimization and numerical simulations are carried out to investigate flow features in a civil transonic fan.With one-dimensional and quasi-three-dimensional axisymmetric methods,a preliminary design of transonic fan has been completed and aerodynamic parameters are analyzed with CFD evaluation.Flow features are investigated to study loss mechanism at rotor tip region and stator corner.Then based on radial equilibrium equation,the hub profile has been optimized.And the results show that optimized hub can impose a favorable radial pressure gradient near the hub to reduce the region of separation in the stator suction surface corner.But it is hard to solve the problem of accumulation of lowmomentum fluid.Controlled curvature optimization and airfoil stacking optimization have been carried out to reduce the corner separation.And the effects of curvature and blade force on the flow are analyzed in detail.The results show that static pressure distribution is closely related to the curvature of camber line.Low-momentum fluid inside suction surface boundary layer can be transported with reasonably curvature distribution,which results in a better pressure field.And it reduces the separation caused by adverse pressure gradient and secondary flow.Stacking optimization method is used to increase the static pressure on the suction surface near the endwall,particularly in highly turning stator,improving the performance over the entire flow range of the transonic fan.Incidence angle of supersonic sections and compression mechanism are taken into account into the aerodynamic optimization of the inlet and outlet metal angle.The flow rate and total pressure ratio are increased while adiabatic efficiency is slightly reduced.The negative curvature is introduced in the leading edge region to control with controlled curvature optimization method again.The results show that the reduction of expansion upstream of the passage shock can be achieved by negative curvature in the front part of the camber line.The pre-shock Mach number and the strength of shock are reduced.The shock induced separation and shock/tip leakage vortex interaction are reduced.Therefore aerodynamic performance of the transonic fan is significantly improved.Finally,the performance of optimal transonic fan at design speed is a total pressure ratio of 1.678,an adiabatic efficiency of 88.47%,and mass flow rate of 30.27kg/s.High efficiency is maintained at off design conditions.