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

Abstract

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.

Two-Phase Flow Modeling and Measurements in Low-Pressure Turbines—Part II: Turbine Wetness Measurement and Comparison to Computational Fluid Dynamics-Predictions

“…As described in Ref. Up to approximately 40% span the computed wetness lies within the measured range and is composed of droplets assigned to the phases FI and P2 (for an explanation of the source-specific drop let representation see Part I of this publication [1]). In Fig.…”

“…The last stage steam turbine test rig at ITSM has been described in Part I of this publication [1] as well as in numerous other publi cations (e.g.. Refs. [23] and [24]), so that the description given here can be very concise and focus on the most important features.…”

“…[ 1 ] for the simulations a calibration of the classical homo geneous nucleation rate is performed. As described in Ref.…”

“…As outlined in the first part of this publication [1], the provision of validation data for numerical calculations of nucleating and condensing steam flows is of great importance, as for example the correct prediction of losses as well as the assessment of erosion threat is directly dependent on the correct prediction of droplet size and number.…”

“…12Comparison of measured and predicted total-static diameters of p1 and p2 at overload condition efficiency of the model steam turbine, from Ref [1]. 12Comparison of measured and predicted total-static diameters of p1 and p2 at overload condition efficiency of the model steam turbine, from Ref [1].…”