In this paper the unsteady flow in inlet valves for large steam turbines used in power stations is investigated using the method of computational fluid dynamics. As the topology of the flow depends on the stroke and the pressure ratio of the valve, it is investigated at several positions. Different turbulence models are applied to the valve in order to capture the unsteady flow field. The RANS, the SAS and the SAS-F (ZFLES) model are evaluated. In order to clarify the cause of flow induced valve vibrations the investigation is focused on the pressure field acting on the valve plug. It could be shown, that acoustic modes are excited by the flow field. These modes cause unsteady forces acting on the valve plug. The influence of valve geometry on the acoustic eigenmodes is investigated in order to lower the dynamic forces. Three major flow topologies are found which crate different dynamic forces.

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