Experimental and Numerical Investigations of the Scale Effect of the Non-Equilibrium Steam in the Flow Patterns

Abstract This research examines the influence of non-equilibrium steam, causing thermodynamic losses due to supercooling and condensation, the major source of wetness losses in low-pressure steam turbines. The non-equilibrium state arises from rapid expansion, deviating from equilibrium phase change behavior, particularly in low-pressure stages with significant expansion and cooling. During development, verification tests using scaled-down model turbines are often conducted. However, few cases investigate the scale effect on performance and flow patterns, especially regarding non-equilibrium phase change phenomena. This research compares measurement results from a full-scale verification test turbine with equilibrium and non-equilibrium steam CFD results for full-scale and scaled-down models. It aims to understand the scale effect of phase change around the low-pressure end stage on flow patterns. While scaling down dimensions, rotational speed is increased to maintain the same Mach number and pressure as the full-scale turbine. However, the steam expansion rate, influencing supercooling and nucleation, differs between full-scale and scaled-down models, leading to differences in thermodynamic losses and flow patterns where phase changes occur. Accurate prediction of non-equilibrium phase change is crucial for designing and optimizing low-pressure steam turbines. Understanding scale effects allows designers to account for differences between model and full-scale turbines, enabling more accurate performance predictions and improved designs. Insights from this research can contribute to developing advanced computational models and numerical techniques for simulating non-equilibrium phase change processes in turbomachinery.