The continuous increase penetration of variable renewable energy and fuel cost requires steam turbine power plants to operate with high flexibility. This situation leads to steam turbines running at very low volume flow (LVF) for an extended time. Ventilation power and temperature predictions have a significant impact on the thermo-economic optimization of the power plant and lifetime assessment of the ventilating stages.

In the last decade with increasing capabilities of CFD and computational resources, significant steps have been made in assessing complex flow behavior. Full size or scaled experimental testing of different last stage blades for a wide range of low load operating conditions is expensive, therefore CFD provides new opportunities in low load calculations. However, prediction of the flow structure in correspondence of the ventilating stages still represents a challenge for the current CFD tools in terms of calculation time and reliability of the results.

There are many different approaches in assessing this phenomenon, however they require significant computer resources and may not be necessary for most industrial applications. This paper presents the CFD modelling of a low-pressure steam turbine based on a direct coupling of the rear stage and exhaust diffuser using a multiple mixing plane approach. Through a comparison with measurements results and more sophisticated methods, it is shown that this approach is able to accurately predict the flow field and hence the ventilation power and temperature at low volume flow.


CFD Modelling of Steam Turbine Last Stage Blades at Low Load Using Multiple Mixing Plane Approach

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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