Unsteady Flow in Extraction Modules of Industrial Steam Turbines

Abstract

Industrial steam turbines are designed for application in power-, process- and chemical engineering. Particular modules ensure the optimum integration into power plants and other engineering processes. Extraction modules allow the controlled extraction of large steam quantities on certain and constant enthalpy levels. Valves regulate the amount of steam extracted from the turbine expansion path. Depending on the valve lift, different flow separation phenomena can occur peripherally inside the valves, causing undesired large unsteady fluid forces on the valve head and seat. Due to the compact design of the industrial steam turbines, these unsteady jets can influence the rotor dynamics as well as the blade loading of the adjacent stages. These fluctuations should be understood and avoided in order to enhance the reliability of steam turbines. In the present study the unsteady flow phenomena due to separation occurring circumferentially inside the valve of extraction modules are investigated numerically. First, the commercial 3D RANS CFD-solver (ANSYS CFX 14) is validated in the application to experimental results. Subsequently, the various flow patterns of the examined valve design are analyzed on a standalone numerical valve model in an extensive study. In order to assess the impact of these unsteady flow separations on other components, the complete extraction module is simulated in combination with the adjacent stages. The transient simulation results show pressure fluctuations downstream of the valves resulting in an unsteady load of the control valves, the shaft and the blading.

Modification of a Steam Valve Diffuser for Enhanced Full Load and Part Load Operation Using Numerical Methods

“…1 Valve plug designs. Sketch by the authors according to Stastny [7] The CFD analyses of Stastny et al [7], Schramm et al [9] and Domnick et al [10] show that steam valves with sharp edged valve plugs provide the desired core flow at wide operation condition but the undesired core flow can still occur at certain operation conditions. These are large valve lifts and small pressure ratios.…”

Introduction of a novel test rig for the investigation of fluid-structure interaction effects in steam turbine control valves using an elastic model

“…This feature is used in various current valve designs e.g. as discussed by Clari et al (2011), Domnick et al (2014) and Schramm et al (2014).…”

“…Due to the poor accessibility and limited publications of data from industrial applications, the experimental data for validation is rare. Based on previous numerical investigations conducted by Schramm et al (2014) at the Ruhr-Universität Bochum, a new test rig was designed. This paper will introduce the new control valve test rig featuring a scaled valve with an elastic valve support.…”