Because of the converging-diverging con guration of the valve passage, venturi valves have been widely used in large turbines to regulate inlet ow as turbine governing valves for about half a century. From the 1960s, a number of valve failure incidents have been reported. Improvement to current designs was strongly demanded but, owing to the complicated nature of the uid-structure interaction mechanisms, the basic mechanism causing valve failure is still far from being fully understood. Experimental investigations on a half-scale valve were performed here. The study con rmed that asymmetric unstable ow is the root cause of valve problems, such as noise, vibration and failure.
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.
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