Unsteady Optimization Of Aerodynamic Performance Of A Turbine Stage

Aerodynamic design is the core content of the axial turbine blade design,which is directly related to turbine efficiency,power and even operation reliability.As the axial turbine towards the direction of high efficiency,high power,economic and compact,higher requirements for its aerodynamic performance are also put forward.In recent years,aerodynamic optimization technology of blade based on CFD steady numerical calculation has been widely developed,but the flow inside the axial turbine passage is unsteady in nature,so it is necessary to conduct aerodynamic optimization design of blade based on unsteady numerical calculation.For the problem of high computational cost in turbine stage unsteady aerodynamic optimization design,this paper proposes a suitable method for single row blade unsteady numerical calculation,called “time-dependent boundary conditions”.The feasibility of this method is verified by LISA 1.5-stage turbine,its main idea is: by applying time-varying unsteady flow parameters at the inlet and outlet boundary of a single row blade to simulate the unsteady effects on the upstream and downstream of the blade,the unsteady calculation of single row blade is successfully carried out.Firstly,the unsteady numerical calculation of the LISA 1.5-stage turbine is carried out and compared with the experimental results.It is found that the unsteady numerical calculation can accurately simulate the real flow condition inside the turbine.And with the wake from upstream blade row diffusing to the downstream blade row,mixing with the main flow,the influence of the relative motion of the rotor and stator blade row,the unsteady phenomenon of each blade row along the axial direction is gradually strengthened.Next,the stacking line parameterization program is developed and integrated with the 3D unsteady numerical calculation of single-row blade.The Latin hypercube design method and the multi-objective genetic algorithm are used to build the aerodynamic optimization design platform for single row blade based on unsteady numerical calculation.Based on the successful aerodynamic optimization platform,the tangential stacking line of the second stator in the LISA 1.5-stage turbine is designed by aerodynamic optimization.The optimization objective is to minimize the total pressure loss coefficient under the condition of constrained mass flow rate and pressure ratio,so as to obtain a positively bowed blade.Let the optimal blade combine with the first stage of the LISA 1.5-stage turbine,the new optimized 1.5-stage turbine is conducted the unsteady numerical calculation.The unsteady results show that the isentropic efficiency of the optimized 1.5-stage turbine is increased by 0.629%,while the total pressure loss coefficient of the second stator is reduced by 12.095%.The blade loading inside the passage is moved up,and the loss at the blade root was significantly reduced.Moreover,the high efficient working range of the turbine is broadened.The unsteady aerodynamic optimization platform established in this paper aims to reduce the computational cost of unsteady numerical simulation of turbine blade and unsteady aerodynamic optimization of turbine blades.