Venturi valves for steam turbines and improved design considerations

Abstract

As a turbine governing valve, the venturi valve has been widely used in large turbines to regulate inlet ow for about 40 years. It is favoured in terms of low total pressure loss because of the convergingdiverging con gurations of the valve passage. However, as turbines become larger and larger, a number of valve failure incidents have been reported, and there is a great demand for improved designs. Yet, because of the complicated nature of the uid-structure interaction mechanisms, the basic mechanism causing valve vibration and failure is still far from being fully understood. Most of the available literature relies heavily on experiments before the 1980s. There are several improved designs by the trial and error method, but governing rules, or even a clear direction for improvement, are almost non-existent. There has still seen no published investigation using computational uid dynamics (CFD) tools. As CFD is increasingly recognized as a powerful tool for understanding complicated uid phenomena, a two-dimensional numerical investigation was performed in the present work. The study revealed that valve plug vibration is due to hydraulic forces acting on the plug at its balanced position and uid-induced excitation as the plug vibrates in the lateral and vertical directions. All this relates to unexpected asymmetric ow patterns. By changing the plug shape, the ow patterns can be made much more symmetric, which reduces the intensity of steady forces and uid plug interaction.

Dynamic behaviour of direct spring loaded pressure relief valves connected to inlet piping: IV review and recommendations

“…Similar instabilities can also be present in other valve topologies e.g. Sverbilov et al (2013); Yao et al (2014), Venturi valves Zhang and Engeda (2003) and hydraulic dampers with blow-down Eyres et al (2005a,b).…”

Analysis of flow-induced instability in a redesigned steam control valve

“…The proposed new designs were found to be better in terms of reduced excitations of valve vibration, especially in large pressure ratio conditions. The work presented here is a continuation of the work of Zhang and Engeda [3] and Zhang et al [4]. The new valve, shown in Fig.…”

“…It has been reported that the flow pattern around the valve is a transonic and separated jet, and as a result, mass flow fluctuations with large pressure fluctuation occurs as described by Widel [1], Araki et al [2] and Zhang and Engeda [3], Zhang et al [4], Morita et al [5], Morita et al [6], Yonezawa et al [7] and Yonezawa et al [8]. As a result steam turbine control valves are known to be a source of noise and vibration.…”

“…Recently a series of investigations carried out by Zhang and Engeda [3] and Zhang et al [4], including experimental, analytical and numerical studies on turbine governor valve to clarify the fluid/ plug interaction mechanism. They confirmed that asymmetric unstable flow was the root cause of valve issues due to the resulting large amplitude unsteady forces, moments and torque.…”

Numerical and experimental research of flow and sound fields in an axial-flow check valve and its optimization

“…MC Sekhar et al 12 studied the spin-transfer torque-induced noise in self-biased differential dual spin valves (DDSVs), showing that self-biased DDSV provided a much stronger stability against spin-transfer torque noise than conventional spin valves. D Zhang and colleagues 13,14 confirmed that the asymmetric unstable flow was the root cause of the valve problems such as vibration and failure. C Bolin and A Engeda 15 further studied the mechanisms of valve instability caused by unsteady flows around the valve and the asymmetric unstable flow, noise, and vibration characteristics of the valve.…”