Entropy generation analysis of wet-steam flow with variation of expansion rate using NURBS-based meshing technique

摘要

In this paper, the entropy generation is introduced as a criterion to analyze the impact of variation of expansion rate in a two-dimensional viscous wet-steam flow through stationary cascades of a steam turbine. In addition, for the first time the NURBS-based mesh generation method is introduced and assessed in the field of wet-steam flow. In the mentioned method, the computational grid with "curved" boundaries is generated by non-uniform rational B-spline (NURBS) surface that describes the geometry of the cascade. The results, which are validated against well-established experiments, reveal that compared to the typical H-type grid, employing the generated NURBS-based mesh significantly reduce the computational error of numerical simulation. According to the obtained results, the prediction errors of static pressure distribution and droplet average radius are reduced by 31% and 78.44%, respectively. Furthermore, it is observed that decreasing the expansion results in moving the nucleation zone toward downstream of the blade and increasing the rate of droplets nucleation. Additionally, the liquid mass fraction as well as the amount of entropy and total entropy generation in the fluid flow increases. (C) 2019 Elsevier Ltd. All rights reserved.