Comparison of Different Strategies to Include Structural Mechanics in the Optimization Process of an Axial Turbine’s Runner Blade

Different strategies to include structural mechanical aspects in the design process of hydraulic machines are compared. Therefore, an axial turbine’s runner blade is optimized using evolutionary algorithms. Four different setups with a scalar objective function are investigated. In the first two setups, structural mechanical aspects are added to the optimization process as a constraint, once with a penalty term and once with a modified selection operator. If structural mechanical aspects are considered as a constraint, the risk of a premature convergence increases. For this reason, additionally, two setups including the minimization of the maximum stress as an objective within a scalar objective function are analyzed. Furthermore, a multi-objective optimization with resolution of the Pareto front is performed. The differences in the results regarding fitness between the setups using a scalar objective function are small. However, the best result is found for a setup where the minimization of the stress is added as an objective. This demonstrates the risk of a premature convergence involved with constraint handling strategies. The worst result is found for the multi-objective optimization with resolution of the Pareto front, most likely due to a less directed search.