Waterpower Engineering

The energy and cavitation performances are the basic characteristics of 2-D cascade. This paper puts forward an optimization design approach for 2-D cascade based on genetic algorithm, aiming at objectives of hydraulic loss and airfoil cavitation erosion.The paper gives a multiobjective optimization design mathematical model of the 2-D cascade. In this model, Singularities Method designs the thicknessless profile initial bone line at first. Based on the acquired bone line, aiming at multiobjectives of cascade loss and profile cavitation erosion, the model searches the best bone line by genetic algorithm. Then the profile is obtained by thickening, the 2-D cascade is obtained consequently. The approach has several characteristics as follows: on one hand, the principle of 2-D cascade design by Singularities Method is simple to accomplish. However because the bone line is designed with thicknessless airfoil, the flow passage becomes narrower after thickening, the velocity of flow becomes larger consequently, the circulation difference between direct problem and inverse problem is big, the bone line needs to modulate, on the other hand, the global search characteristic of genetic algorithm is an advantage for searching the best thickness distribution. Combining the advantages of the two methods in the 2-D cascade design is a new trial in this field, which can not only meet the given circulation level of the cascade, but also increase the efficiency and decrease the airfoil cavitation erosion. The paper applies the aforesaid approach to the design of ZZ440 cascade, which is completed by Fortran PowerStation computer language. By comparing the cascade performance before and after optimization, the optimization result shows that the method is efficient andfeasible.