The purpose of the ''International Wet Steam Modeling Project'' is to review the ability of computational methods to predict condensing steam flows. The results of numerous wet-steam methods are compared with each other and with experimental data for several nozzle test cases. The spread of computed results is quite noticeable and the present paper endeavours to explain some of the reasons for this. Generally, however, the results confirm that reasonable agreement with experiment is obtained by using classical homogeneous nucleation theory corrected for non-isothermal effects, combined with Young's droplet growth model. Some calibration of the latter is however required. The equation of state is also shown to have a significant impact on the location of the Wilson point, thus adding to the uncertainty surrounding the condensation theory. With respect to the validation of wet-steam models it is shown that some of the commonly used nozzle test cases have design deficiencies which are particularly apparent in the context of two-and three-dimensional computations. In particular, it is difficult to separate out condensation phenomena from boundary layer effects unless the nozzle geometry is carefully designed to provide near-one-dimensional flow.

A numerical study on the flow in a three stage low pressure industrial steam turbine with conical friction bolts in the last stage and lacing wires in the penultimate stage is presented and analyzed. Structured high-resolution hexahedral meshes are used for all three stages and the meshing methodology is shown for the rotor with friction bolts and blade reinforcements. Modern three-dimensional CFD with a non-equilibrium wet steam model is used to examine the aero-thermodynamic effects of the part-span connectors. A performance assessment of the coupled blades at part load, design and overload condition is presented and compared with measurement data from an industrial steam turbine test rig. Detailed flow field analyses and a comparison of blade loading between configurations with and without part-span connectors are presented in this paper. The results show significant interaction of the cross flow vortex along the part-span connector with the blade passage flow causing aerodynamic losses. This is the first time that part-span connectors are being analyzed using a non-equilibrium wet steam model. It is shown that additional wetness losses are induced by these elements.

The three-stage low-pressure model steam turbine at the Institute of Thermal Turbomachinery and Machinery Laboratory (ITSM) was used to study the impact of three different steam inlet temperatures on the homogeneous condensation process and the resulting wetness topology. The droplet spectrum as well as the particle number concentration were measured in front of the last stage using an optical-pneumatic probe. At design load, condensation starts inside the stator of the second stage. A change in the steam inlet temperature is able to shift the location of condensation onset within the blade row up- or downstream and even into adjoining blade passages, which leads to significantly different local droplet sizes and wetness fractions due to different local expansion rates. The measured results are compared to steady three-dimensional computational fluid dynamics calculations. The predicted nucleation zones could be largely confirmed by the measurements. Although the trend of measured and calculated droplet size across the span is satisfactory, there are considerable differences between the measured and computed droplet spectrum and wetness fractions.

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 model ing, 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 mod els 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 experi mental 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 investi gated 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 publi cation focuses on experimental investigations and compares the numerical results to wetness measurement data. For this purpose, different loads are also considered.

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.