Suppression of the Flow Oscillation on the Steam Control Valve

Abstract

It is well known that a steam control valve may cause severe flow vibration at partial valve opening, in thermal or nuclear power plants. For the rationalization of maintenance and management of the plant, the vibration should be avoided. However, it is difficult to understand the flow characteristics in detail only by experiments because the flow around the valve would he very complicated with 3 D supersonic structure. Under this circumstances, the application of the latest CFD (Computational Fluid Dynamics) technology is useful for the clarification of the cause of the vibration and the examination of the methods for suppression. In our previous research, it was found by combining experiments and CFD that the interaction of the flow attached to the valve body causes a pseudo-periodic spike type pressure fluctuation at partial valve opening. Since this pressure fluctuation results in cyclic side load on the valve body, it will cause lateral vibration of the valve body. In the present report, several geometries are proposed and examined for the suppression of the flow oscillation at the partial valve opening, based on the understanding of the mechanisms of the flow oscillation as mentioned above. First, the change of the valve seat geometry such that the flow is enhanced to attach to the valve seat was examined. Although some effects could be found, we could not succeed in completely suppressing the oscillation. Then, two types of valve body geometry, which would prevent the flow attachment to the valve body are proposed and examined. It was found that one of them could completely avoid the flow oscillation.