Comparison of Steam Turbine Control Valve Geometries and their Dynamic Behaviour at Part Load

Authors

Christian Windemuth  - Technische Universität Dresden, Institute of Fluid Mechanics, Chair of Turbomachinery and Flight Propulsion, Germany
Martin Lange - Technische Universität Dresden, Institute of Fluid Mechanics, Chair of Turbomachinery and Flight Propulsion, Germany
Ronald Mailach - Technische Universität Dresden, Institute of Fluid Mechanics, Chair of Turbomachinery and Flight Propulsion, Germany

Abstract

A growing significance of flexible steam turbine operation challenges the regulation of turbines. Part load operation by the use of control valves can be accompanied by highly unsteady flow conditions. The increased dynamic load induced by resulting pressure forces can reduce the safe and reliable operating range, weaken the valve and at its worst lead to mechanical failures.The geometry of the valve takes a major role in the reduction of dynamic forces. Using a scaled control valve, experiments in a model valve rig were conducted using compressed air. With the focus on the dynamic behaviour of the valve head, flow rate, pressure, vibration and force measurements were analysed. A circular valve shape favouring unstable operation was used as a reference case and the desired instability was proven by measurements. Different modified valve geometries based on literature featuring separation edges were then tested against the circular shape. Results indicate the improved stability of the modified geometries over the circular shape. For most of the operating range, vibrations were drastically reduced and the overall flow stabilized.