Design analysis of high and low loaded high- and low-pressure axial-flow turbines for a single shaft 50 MWe supercritical carbon dioxide Brayton power cycle

Abstract

This paper presents the design optimization of high- and low-pressure axial-flow turbines within the context of a 50 MWe supercritical carbon dioxide (sCO₂) Brayton power cycle. The study aims to evaluate and compare different loading design philosophies, emphasizing the balance between isentropic efficiency and mechanical stress. First, a mean line analysis code was developed, which was validated via CFD simulation and then used to generate a design of experiments datasets by changing various design parameters for both high- and low-loading conditions. Through an analysis of the design variables, the research identifies optimal turbine configurations that maximize efficiency while minimizing peak rotor stresses and overall volume. The results indicate that the selected non-dominant optimal solutions effectively exhibit a trade-off between efficiency and mechanical integrity. Notably, the optimal designs yield a 3 % reduction in efficiency relative to the highest efficiency designs for only a 29 % increase in peak rotor stress compared to the lowest stress designs. The findings reveal that for high-loading turbine designs, exceeding 90 % efficiency as a design objective results in a significant increase in peak rotor stress, necessitating careful consideration of operational limits. Additionally, the paper presents Pareto fronts for non-dominating optimal solutions, highlighting the effectiveness of low-loading designs in maintaining a balance between efficiency and structural performance.