Vortex-Generators Reduce the Dynamic Axial Forces in the Model of a Steam Turbine Control Valve

Abstract

Abstract Control valves of steam turbines are exposed to large static and dynamic forces caused by pressure fluctuations, turbulence and other influences, especially in part-load operation. Excitation of acoustic modes in cavities is one of these causes that leads to fluctuating forces on parts of the valve especially the valve plug. In control valves, the acoustic mode can be excited by unstable periodic behaviour such as shear layer flow. This shear layer flow occurs behind the valve seat in the diffuser between the wall jet and a backflow region in the core of the diffuser. This paper describes the occurrence of increased fluctuating axial forces on the valve plug in a control valve for steam turbines due to the excitation of an acoustic mode in the rear cavity between the valve plug and the valve cover. In the first step, an initial geometry is investigated in a test rig. The occurrence of an acoustic mode and the effects on the valve plug were measured using force, pressure and displacement sensors. The results are presented in this paper and compared to numerical results from previous studies. In the second step, vortex-generators are installed in the same model valve and their effects on the excitation of the acoustic mode in the rear cavity are investigated. It is shown that the vortex-generators upstream of the valve seat effectively create vortices that affect the flow topology downstream of the valve seat. This weakens the excitation of the acoustic mode and reduces the axial forces.