This work presents guidelines for designing a ring-type inlet duct of an intermediate pressure steam turbine. It looks at aerodynamic characteristics of the flow field in the analyzed ducts as well as the impact of the duct topology on the radial clearances influencing casing deformations in different load cases. To show the reliability of the CFD-program used, calculated results are compared to measured data. The numerical method reflects the main physical effects observed in the reference cases with high accuracy. The inlet duct shape influences the loss of total pressure within the duct and the following stator blades as well as the leakage losses in the whole turbine casing. To minimize these losses, geometric parameters such as area ratios within the duct and the shape of its flow channels, are considered and the influence of these parameters on the losses is quantified. The optimization of the inlet duct leads to a geometry with minimum losses from an aerodynamic and mechanical point of view.

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