Abstract
The design of modern steam turbines for power plant applications is steering towards higher efficiencies. A considerable contribution to this aim is expected from a reduction of flow losses in turbine intakes and exhausts. The present study therefore deals with the optimisation of the exhaust of a high-pressure (HP) turbine. In the first part of this study a numerical model is presented which allows for a precise representation of the exhaust flow. This computational fluid dynamics (CFD) model has been validated with a fair amount of experimental data from a test rig. For the second part of the study comprehensive numerical investigations have been carried out, considering the major geometrical parameters of such a geometry. In order to minimize the effort in design time and preprocessing a fully parametric 3D model of the geometry is created to prepare the different design variations. The results of these simulations allow to assess the performance differences of given exhaust designs in the early design phase without the need for expensive CFD simulations. Finally a potential for improvement of 300 kW for a 800 MW power plant is shown by means of a comparison of an optimised design to the baseline geometry.
Highlights
Besides the effort to further increase the efficiency of modern steam turbine power plants, the design of the turbine is driven by a demand to reduce costs
As a resume of the results presented so far, it can be stated that all turbulence models are capable to predict the time average flow field good enough for the purposes of this paper
The k − ω turbulence model is chosen as it best fit the experimental data, any of the investigated eddy viscosity turbulence models are able to predict the main flow phenomena. This numerical model is used in a parameter study to evaluate the main geometric parameters of the ring chamber cross-section influencing the performance of the turbine exhaust
Summary
Besides the effort to further increase the efficiency of modern steam turbine power plants, the design of the turbine is driven by a demand to reduce costs. The design consists of an axial-radial diffuser to recover some of the kinetic energy and reduce the inlet velocity to the ring chamber which is responsible to collect the steam and guide it to the successive piping. In all those designs, a vortex will form in the exhaust ring chamber which is a major source for flow losses.
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