In order to develop the next generation of low pressure steam turbines, it is imperative to understand the moisture effects and their impact on performance. The objective of the current study is to apply the recently developed in-house multiphase CFD code to the analysis of the tip section of the last stage bucket (LSB), and propose design improvements based on insights gained into wet steam flow physics. 2D simulations were first carried out with equilibrium and non-equilibrium condensation models, showing significant differences in losses which were attributed to non-equilibrium condensation. Details of the shock structures in the transonic blade tip passage under equilibrium and non-equilibrium condensation models were captured with best in class split blade grid topology. Sensitivity studies of major airfoil design parameters such as un-guided turning and trailing edge angle were carried out and their impact quantified on the basis of wetness losses. Based on the detailed investigation of the flow field, a new design feature on the suction side of the LSB was proposed. Numerical results show higher performance benefit of the new design at design point operation.

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