Numerical Investigation of Wet Inflow in Steam Turbine Cascades Using NURBS-based Mesh Generation Method

Abstract

In this paper, the impact of existence of wetness in the inflow of stationary cascades of steam turbine blades has been numerically investigated. A new mesh generation method based on non-uniform rational B-splines (NURBS) has been adopted to reduce the numerical error of the wet inflow simulation. Moreover, two common meshing scenarios namely blade-to-blade (B-B) and periodic-to-periodic boundary (P-P) are studied and different angle of the grid at the trailing edge have been considered. The classical nucleation theory corrected by Courtney–Kantrowitz model and the Young's droplet growth model are employed to simulate the condensation phenomenon. By validating against experimental data, the results showed that implementing the proposed NURBS-based meshing technique decreased the prediction errors of static pressure distribution and droplet average radius by 35.64% and 78.44%, respectively, in comparison to typical grid generation methods. In addition, it was observed that existence of wetness at inlet significantly decreased the supercooling degree and postponed the nucleation process. Thus, the nucleation rate could be ameliorated in the case when we have a specific amount of wetness fraction in the inflow.