Optimization of multista ge turbinesusing a through-flow code

Abstract

Very fast and accurate flow calculation and performance pre-diction of multistage axial flow turbines at design and o-design conditions was perfo rmed using a compressible steady state in-viscid through-ow code with high delity loss and mixing mod-els. The code is based on a stream function model and a finite element solution procedure. A new designsystem has been de-veloped which optimizes hub and shroud geometry and inlet and exit o w-field parameters for each blade row of a multistage axial flow turbine. Optimization was perfo rmed using our hybrid con-strained optimization code that includes the follo wing modules: genetic algorithm, simulated annealing, modified simplex method, sequential quadratic programming, and a gradient search algo-rithm. Switching among the modules was performed automati-cally. By varying a relatively small number of geometric variables per each turbine stage it is possible to find an optimal radial dis-tribution of flow parameters at the inlet and outlet of every blade row. Thus, an optimized meridional flow path can be found that is defined by the optimized shape of the hub and shroud. The mul-tistage design optimization system has been demonstrated using an actual tw o-stage axial gas turbine as an example. The compar-ison of computed performance of an already very high efficiency initial design and its optimized design demonstrates more than one percent improvement in the turbine efficiency at design and significant o-design conditions. The entire design optimization process is feasible on a typical single-processo r computer worksta-tion or a personal computer.