Study On Aerodynamic Optimization Design Of Turbine Under The Influence Of Multiple Factors

Turbine is one of the core components of the aircraft engine.Aerodynamic efficiency is an important indicator of turbines.The shape design of turbine blade and endwall is the direct factor that affects the aerodynamic efficiency.The purpose of this paper is to conduct aerodynamic optimization design research of turbine blade and endwall modeling considering various factors.A nonaxisymmetric endwall automated optimization process based on nonuniform rational B-spline surface(NURBS)technique is proposed.This optimization process is applied for the aerodynamic optimization of the turbine stator shroud to reduce total pressure loss and secondary kinetic energy.The flow fields of the original endwall design and optimization design(Opt1)are investigated and compared.The results show that Opt1 design reduced total pressure loss and secondary kinetic energy coefficient by 11.1% and 11.0%.The decrease in secondary kinetic energy could be attributed to reduction in horseshoe vortex and the reduced transverse pressure gradient.Quantitative loss analysis is performed with a loss breakdown method.As secondary flow loss is much smaller than profile loss,reduced profile loss contributes more to overall aerodynamic performance improvement.When the outlet Mach numbers and inlet incidence angles vary,the aerodynamic performance of the optimized endwall design is always better than the original design.The nonaxisymmetric endwall optimization design(Opt2)is performed again in the stage environment.The effects of different optimization schemes on the aerodynamic performance of the turbine stage are compared and analyzed.Compared with the original design,the losses of stator and rotor are suppressed in both optimization schemes.However,the main gain in stage efficiency improvement of the Opt1 design comes from the stator blade,and the main benefit in stage efficiency improvement of the Opt2 design comes from the rotor blade.A study on the effect of purge flow on the aerodynamic performance of turbine is carried out to verify the performance improvement of the nonaxisymmetric endwall design in the real environment with purge flow.First,a nonaxisymmetric endwall optimization design for the rotor hub is processed to evaluate its influence on the aerodynamic performance of the turbine stage.Then,to study the influence of the purge flow on the nonaxisymmetric endwall,the flow field and aerodynamic performance of the turbine stage with and without purge flow are compared.The research shows that the profiled endwall affects the migration path of the sealing cold air after entering the rotor blade and weakens the shear-induced vortex.The turbine stage efficiency decreases as the mass flow rate of the purge gas increases.Compared with the original design,the turbine stage efficiency of the nonaxisymmetric endwall design is improved under different mass flow rates(0,0.1%,0.5%,0.9%,1.3%,1.7%)of the purge gas.The heat transfer performance of the optimization design is checked.Compared with the original design,the endwall average film cooling efficiency of the nonaxisymmetric endwall design is reduced,but the endwall average Nusselt number is also decreased.The combined modeling of non-axisymmetric end walls and 3D blades will increase the geometric freedom in aerodynamic design.The joint design of the nonaxisymmetric endwall and the 3D blade is carried out in the stage environment.The effects of curved blade,nonaxisymmetric endwall and joint design on aerodynamic performance are investigated.The results show that joint design is more helpful to improve the stage aerodynamic performance.Compared with the original design,the joint optimization design(NEW2A42),the separate nonaxisymmetric endwall optimization design(NEW1A0)and the separate curved blade optimization design(AEWA45)reduce the total loss of the turbine stage by 0.32%,0.18% and 0.18% respectively.The heat transfer performance of the joint optimization design(NEW2A42)is checked.Compared with the original design,the endwall average Nusselt number is decreased.To improve the aerodynamic efficiency and ensure the heat transfer performance at the same time during aerodynamic optimization design of turbine blades,a new simplified conjugate heat transfer(CHT)method based on the onedimensional pipe-network method and three-dimensional(3D)CFD is proposed.Compared with the full 3D CHT method,the new method can save computing resources.The simplified CHT method and the full 3D CHT method are used to simulate the MARK-Ⅱ airfoil under multiple working conditions.The calculation results of the two numerical calculation methods are compared with the experimental data,which verifies the feasibility of the calculation method in this paper.Based on the simplified CHT method,a blade profile aerodynamic optimization design platform considering heat transfer is established.The blade profile of the second stage rotor blade of an aero-engine turbine is optimized using this platform.The aerodynamic efficiency increases by 0.34% and the cold air mass flow is reduced by 7.66%.Besides,the change of the blade average temperature is small.