Numerical Study on the Influence of Surface Tension Correction Coefficient on Non-Equilibrium Condensation Flow of Wet Steam in the Last Stage of Steam Turbine

Aiming at the sensitivity of the droplet nucleation rate in the wet steam non-equilibrium condensation flow model to the value of the surface tension correction coefficient (NBTF), and to avoid the subjectivity and uncertainty in its selection, this study calibrated the quantitative relationship between the optimal NBTF values and the inlet pressure and inlet superheat degree across 81 operating conditions. This was achieved by comparing numerical simulations with experimental data from multiple sets of wet steam condensation flow experiments documented in the literature. Subsequently, a bivariate regression equation capable of directly predicting NBTF was established using the mathematical method of statistical regression analysis. The reliability of the equation was verified using the results of an independent experiment (the Dykas cascade experiment). Furthermore, taking the last stage of a certain marine steam turbine as the research object, the established equation was applied to conduct a numerical study of wet steam non-equilibrium condensation flow. The influence of the NBTF value on the nucleation process, droplet distribution, and flow loss was quantitatively analyzed. The results indicate that within a specific range (inlet pressure 15~280 kPa, inlet superheat degree −12~50 K), NBTF shows a significant positive correlation with inlet pressure and a significant negative correlation with inlet superheat degree. The value of NBTF directly affects the prediction results of droplet nucleation rate, particle size distribution, and condensation zone location within the last stage of the steam turbine. This research provides a data-based, reproducible prediction tool for determining the NBTF value in the numerical simulation of wet steam condensation flow and also offers a quantitative reference for the anti-water erosion design and operational optimization of the last stage of steam turbines.