Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines-Part I: Numerical Validation of Wet Steam Models and Turbine Modeling

In this publication, an overview of the current state of wetness modeling at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) is given. For the modeling, an Euler-Euler method implemented in the commercial flow solver ANSYS CFX is used. This method is able to take into account the nonequilibrium state of the steam and models the interactions between the gaseous and liquid phases. This paper is the first part of a two-part publication and deals with the numerical validation of wet steam models by means of condensing nozzle and cascade flows. A number of issues with regard to the quality of the computational fluid dynamics (CFD) code and the applied condensation models are addressed comparing the results to measurements. It can be concluded that a calibration of the models is necessary to achieve a satisfying agreement with the experimental results. Moreover, the modeling of the low pressure model steam turbine operated at the ITSM is described focusing on the asymmetric flow field in the last stage caused by the axial-radial diffuser. Different simplified axisymmetric diffuser models are investigated in steady state simulations, and the results and the arising issues for part-load, design-load, and over-load conditions are discussed. Thereafter, a comparison between the equilibrium and nonequilibrium steam modeling approaches is performed and the advantage of the nonequilibrium model is highlighted. The second part of the publication focuses on experimental investigations and compares the numerical results to wetness measurement data. For this purpose, different loads are also considered.