Prediction and Guideline for Evaluation of Flow-Induced In-Line Oscillation of a Cylindrical Structure in the Bubbly Flow of the Pipe System.

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This study are for providing important data to support and develop "Guideline for Evaluation of Flow-Induced Vibration of a Cylindrical Structure in a Pipe" by the Japan Society of Mechanical Engineers, Standard JSME S012-1998. Flow-induced in-line oscillation of a cantilevered circular cylinder model like a thermocouple that is actually used in industrial plants has been experimentally studied by free-oscillation tests in a water tunnel.Free- oscillation test for a cantilevered model like a thermocouple in a water (a single- phase flow): The response tip amplitudes of a circular cylinder were measured at varying reduced velocity from 1.0 to 4.0. A cantilevered cylinder was supported by plate spring mounted on the water tunnel wall. The aspect ratio of a cylinder was varied from 5 to 21 to investigate the effect of aspect ratio on the response amplitude. It is found that the cylinders with aspect ratio of 5 and 10 show one excitation region, but the cylinders with aspect ratio of 14 an … More d 21 showed two excitation regions. The aspect ratio, therefore, strongly affects the amplitude of the second excitation region. The influence of end-effect also was investigated using cylinders with an end plate attached on the free end. Because the cylinders with an end plate show two excitation regions even if the cylinder has an aspect ratio of 5, the flow around the free end of cantilevered cylinder makes the end-effect. The mechanism of vibration was investigated using a cylinder with a splitter plate in wake to prevent the alternate vortices. The amplitude is bigger than normal cylinder especially at the reduced velocity from 2.3 to 3.0 where the cylinder attached an end plate shows the second excitation region; that is to say, the alternate vortices suppress the amplitude in this range. The maximum amplitude of each excitation region decreases in proportion to the reduced dumping parameter and the amplitude of the first excitation is more sensitive to that parameter. The amplitudes are suppressed in each excitation region when the reduced dumping parameter is greater than 2.5 with each aspect ratio of 10 and 21.Free- oscillation test for a cantilevered model in two-phase flow: As the fundamental study on flow-induced in-line oscillation of a cantilevered circular cylinder model in two-phase flow, the variations of void fraction, bubble diameter and bubble velocity are measured using an electrical resistivity probe when two-phase flow goes through the region of sudden area expansion in the vertical pipe. In this study two different radial void distributions in the pipe are considered. One is called as sliding flow regime, which occurs when the bubble diameters are less than 5mm. The other is termed as coring flow regime, which takes place when the bubble diameters are greater than 5mm. And the response amplitudes of a circular cylinder have been measured by the free-oscillation tests in the two-phase flow in a water tunnel. Comparing the response amplitudes with the results in a water, we found that the flow-induced vibration are suppressed by the two phase flow. Less