In order to enhance steam mass flow through a turbine it becomes necessary to reduce the flow resistance of the turbine inlet valves. Consequently, a replacement of the high pressure turbine inlet valves is required. The valve combination described in this paper consists of a control valve and an emergency stop valve, opposite to the control valve. Both valves share a common valve seat. The control valve is a single-seat valve with integral pilot disc. A pre-stoke is introduced to allow for moderate opening forces. The emergency stop valve closes in countercurrent with the steam mass flow.

The flow through the valve is analyzed by steady state and transient computational flow simulations. In addition to the steam mass flow, the forces acting upon the valve are determined. Transient behavior will be investigated by means of analyzing pressure fluctuations. Therefore frequencies caused by the steam flow are determined in the range up to 2000Hz.

It will be shown that neither steady state nor transient simulations with a simple eddy viscosity turbulence model are capable to correctly predict the complex flow inside the valve. More sophisticated turbulence modeling like Large-Eddy simulation is thus inevitable. Furthermore, the physical phenomena causing the transient behavior are discussed. All findings are verified by comparison of the CFD with the measurements.

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