TWO-PHASE FLOW MODELING AND MEASUREMENTS IN LOW-PRESSURE TURBINES - PART 1: 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 non-equilibrium 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 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 non-equilibrium steam modeling approaches is performed and the advantage of the non-equilibrium model is highlighted. The second part of the publication focuses on experimental investigations and compares the numerical results to wetness measurement data, see Schatz et al. [1]. For this purpose, also different load conditions are considered.