Control valve is an accident prone equipment in high-parameter steam turbine, and its safety directly influences the economy and safety of the unit. In this study, a control valve of a 600 MW subcritical unit used in the power plant was investigated to reveal the mechanism of flow induced vibration of the control valve. It is found that the intermittent vibration of the control valve is a fluid-solid interaction phenomenon, which occurs in middle-opening and transonic flow condition. The phenomenon is a variable damping and nonlinear vibration for the valve stem system. The experimental results show that as the valve head tilts to different positions, the pressure fluctuation at the valve seat changes significantly at the same time. Unsteady numerical simulation is conducted when valve head is in the center and tilts toward three different directions with the same angle. The results indicate that the separation point between the high jet flow and valve head is changing with time. The thick boundary layer caused by transonic flow and the moving high-pressure region induced by impinging jet flow are the two main reasons for the flow pattern alternation. The average unbalanced force of fluid acting on valve head varies as the flow pattern alternates. And its direction is from center to the narrower side of the annular channel in the oblique section when valve head is tilted.

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