Clemens Bernhard Domnick

Numerical Investigation on the Vibration of Steam Turbine Inlet Valves and the Feedback to the Dynamic Flow Field

The power output of steam turbines is controlled by steam turbine inlet valves. These valves have a large flow capacity and dissipate in throttled operation a huge amount of energy. Due to that, high dynamic forces occur in the valve which can cause undesired valve vibrations.In this paper, the structural dynamics of a valve are analysed. The dynamic steam forces obtained by previous computational fluid dynamic (CFD) calculations at different operating points are impressed on the structural dynamic finite element model (FEM) of the valve. Due to frictional forces at the piston rings and contact effects at the bushings of the valve plug and the valve stem the structural dynamic FEM is highly nonlinear and has to be solved in the time domain.Prior to the actual investigation grid and time step studies are carried out. Also the effect of the temperature distribution within the valve stem is discussed and the influence of the valve actuator on the vibrations is analysed.In the first step, the vibrations generated by the fluid forces are investigated. The effects of the piston rings on the structural dynamics are discussed. It is found, that the piston rings are able to reduce the vibration significantly by frictional damping. In the second step, the effect of the moving valve plug on the dynamic flow in the valve is analysed. The time dependent displacement of the valve is transferred to CFD calculations using deformable meshes. With this one way coupling method the response of the flow to the vibrations is analysed.© 2015 ASME

Numerical Investigation on the Time-Variant Flow Field and Dynamic Forces Acting in Steam Turbine Inlet Valves

The unsteady flow in inlet valves for large steam turbines used in power stations was investigated using the method of computational fluid dynamics (CFD). As the topology of the flow depends on the stroke and the pressure ratio of the valve, the flow was investigated at several positions. Various turbulence models were applied to the valve to capture the unsteady flow field. Basic Reynolds-averaged Navier–Stokes (RANS) models, the scale adaptive simulation (SAS), and the scale adaptive simulation with zonal forcing (SAS-F, also called ZFLES) were evaluated. To clarify the cause of flow-induced valve vibrations, the investigation focused on the pressure field acting on the valve plug. It can be shown that acoustic modes are excited by the flow field. These modes cause unsteady forces that act on the valve plug. The influence of valve geometry on the acoustic eigenmodes was investigated to determine how to reduce the dynamic forces. Three major flow topologies that create different dynamic forces were identified.

Computational Study of Kelvin-Helmholtz Instability Created by Interaction of the Mainstream Flow and the Seal Flow in Gas Turbines

The present paper gives a contribution to a better understanding of the emergence of Kelvin-Helmholtz instabilities (KHI) in gas turbines. In an earlier paper of the authors, the occurrence of the KHI’s near the rim cavity of a 1.5 stage gas turbine has been examined by use of CFD methods. It is shown that the KHI’s occur, when the swirl component of the hot gas flow is very strong. Due to the fact, that a high swirl is produced by the guide vanes of the first stage, this matter concerns all common gas turbines. In order to get a basic theoretical background of the emergence of the KHI’s, 2D CFD investigations of the flow behind a splitter plate have been performed showing the development of KHI’s downstream of the splitter plate. To validate the numerical results a comparison to test rig data is used. This shows that the numerical method can simulate the characteristics of the KHI’s. Furthermore, a parameter study is conducted to extract parameters describing the appearance of KHI’s, the vortex periodicity and stability criteria. The main intention of this paper is to deliver “KHI parameters”, which are able to describe the development of the KHI in gas turbine rim cavities.Copyright