抄録
In a petroleum, gas or chemical plant, a valve is installed in piping system to automatically regulate the gas pressure in the upstream chamber. The gas flows through the valve at a high speed, often as a supersonic flow, which causes oscillatory phenomena of flow. The flow directly impinges on the pipe and vibrates the pipe wall, which leads to a fatigue failure of pipe elements for a short time in the worst case. The damage of a joint, in particular, where the pipe meets a large-diameter pipe downstream of the valve, is responsible for one of the critical accidents. To clarify a mechanism of "flow-induced vibration" like this, a transonic flow was examined which is established in a pipe with enlargement of cross-sectional area immediately downstream of a convergent nozzle. The vibration of the pipe is measured using strain gauges and a noise emitted from the pipe end is also measured to understand the conditions in the pipe. As a result, some dominant frequencies were found from analyzing the pipe vibration and the sound pressure wave. As the supply pressure increases, these frequencies gradually rise and approach the natural frequencies of an acoustic field in the pipe within a certain supply pressure range. Furthermore, the measurements of pipe vibration and sound pressure agree well with each other.
