Unsteady CFD Simulation of Control Valve in Throttling Conditions and Comparison With Experiments

Abstract

The operational flexibility of steam power plant is becoming more important as power generation becomes increasingly decentralized, with a growing contribution from renewable energy sources. In a power plant the control valve is a key component to guarantee the control of the plant of which is increasingly demanded to extend the operational capability. At specific operating conditions, the control valve could experience vibrations. In this paper, the physical phenomena of the unsteady aerodynamic excitation force have been investigated by means of CFD techniques. An in-house code was used to simulate the flow-induced vibration. Unsteady transonic 3D simulation generally requires huge computational effort. A novel unsteady quasi-3D approach has been developed and applied as pre-design tool to establish the qualitatively operational map of the valve and to detect the critical operational range, to reduce the number of detailed 3D simulations. The numerical results are compared with experimental test undertaken in the Central Research Institute of Electric Power Industry [4] and full 3D simulation performed with the commercial tool CFX, using the Scale-Adaptive Simulation (SaS) turbulence model. Different pressure drops at certain lift have been selected from the operational map and reproduced numerically. Different modes have been identified, from stochastic behavior with wide width of frequency to periodic flow with one dominant frequency. Results indicate good agreement between the predicted frequency and amplitude and benchmark experiments. The quasi-3D simulation is able to reproduce the principle behavior of the flow field for different drop of pressure and capture the different operational mode. Similar behaviour has been detected also for the selected operating condition in the full 3D analysis. In addition, flutter calculation of the downstream pipe is carried out. It has demonstrated that the implementation of oscillating discharge piping influences the amplitudes and frequency of the upstream flow region.

Numerical Analysis of the Unsteady Loads on a Steam Turbine Double Seat Control Valve

“…This idea can be applied theoretically to any turbulence model, although most applications of the SAS principle are conducted on the basis of the k − ω SST model following the work of Menter and Egorov [14]. This work, based on the procedure proposed and validated by Zanazzi et al [7], exploits the k − ω SST SAS model in the version implemented within the commercial CFD code Anysys CFX v14. 5.…”

“…More recently Zanazzi et al [7] performed a numerical investigation of the unsteady behavior of a steam turbine partition valve in throttling conditions. This work compared a simplified in-house procedure with full 3-D Computational Fluid Dynamics (CFD) analysis and experiments available for a single seat valve with axisymmetric stem under a large number of working conditions characterized by five different unsteady modes.…”

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

“…In addition to the experimental research, various numerical investigations were conducted on several different valve geometries. The fluid-structure interaction in the spherical valve design investigated by Morita et al (2004) was further investigated by Zanazzi et al (2013) using numerical methods. For a can shaped valve design several publications by Domnick et al (2014Domnick et al ( , 2015Domnick et al ( , 2016 discuss part load performance and resulting flow patterns and reaction forces, considering fluid-structure interaction effects.…”

Unsteady behavior of wall-detached flow inside a steam turbine control valve

“…Furthermore, unsteady flow behaviors inside the control valves have been investigated through high-fidelity numerical simulations such as scale-adaptive simulation (SAS), detached-eddy simulation (DES), and large-eddy simulation (LES). For traditional valves with a spherical spindle, Morita et al 13 performed LES on a scaled-down model, and they found that the unstable wall-detached flow induced a cyclic asymmetric side load to the valve spindle; the SAS of Zanazzi et al 14 showed that unstable wall-detached flow also resulted in severe shock-wave oscillations inside the downstream pipe. Subsequently, Yonezawa et al 15 conducted DESs with experimental validation for a cutoff control valve; their numerical results demonstrated that wall-detached flow introduced a rotating high-pressure region acting on the valve spindle, yielding a periodically fluctuating lateral force.…”