Abstract This study investigates the aerodynamic design and analysis of a low aspect ratio, multistage, axial-flow turbine for integration in sCO2 power cycles. The secondary flows developing across the flow path are analyzed using low- and high-fidelity modelling approaches, to evaluate their impact on aerodynamic performance. A low-fidelity design tool, developed in-house at Politecnico di Milano, was coupled to a non-linear optimization algorithm to create an optimized mean-line design of a five-stage axial flow sCO2 turbine, resulting in an optimal total-total efficiency of 93.9%. Fully 3D numerical simulations of the turbine first stage, which features the lowest aspect ratio blades (approximately 0.5), were performed using both steady-state and time-resolved approaches. The impact of vortex - blade and vortex - vortex interactions on the stage efficiency was highlighted, with unsteady interactions causing 10% higher secondary losses compared to the steady-state model. Fully 3D numerical simulations of the complete five-stage axial sCO2 turbine were finally performed to investigate the development of secondary flows in a multistage configuration. The secondary loss estimates obtained by the CFD simulations were compared with those evaluated by applying multiple empirical loss correlations. Results indicate that literature-based empirical loss correlations provide acceptable estimates of the overall turbine performance, but a margin of improvement is evident on the estimate of secondary losses, which appears overly conservative for blades with aspect ratio lower than 1. Conversely, industrial correlations developed in-house more closely align with high-fidelity results.
Saleem et al. (Mon,) studied this question.
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