Research and Development on Shapes of Non-Vibrational Thermocouple in the Pipe System of Industrial Plants

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Flow-induced oscillation of circular and rectangular cylinders were studied by free-oscillation tests in a water tunnel and a wind tunnel and also by numerical simulations. Flow-induced oscillation of bluff bodies occurs in industrial plants such as nuclear power plants, petroleum/chemical plants and offshore platforms. Usually, a thermocouple and a sensor probe are inserted in the pipe system. If the working fluid is a liquid, such cantilever-shaped structures with extremely small mass ratios may be easily induced by the flow to oscillate. We carried out multiple experimental and numerical studies where cylinders were elastically supported at both ends and where the cylinder was cantilevered. The main conclusions to obtained from these experiments and numerical simulations are as follows.(1)The response characteristics of cylinders with aspect ratios of 5 and 10 show single excitation region in the range of reduced velocity Vr from 1.0 to 4.0, in contrast to the cylinders with aspect … More ratios of 14 and 21. Most notably, the aspect ratio affects the depth of valley between the first and second excitation regions and the amplitudes of the second excitation regions.(2)It was found that cylinders with taper ratios of 2.5% to 10% had two excitation regions, while cylinders with taper ratios less than 1% had one excitation region. The taper ratio, therefore, affects the amplitude of the second excitation region. The reference diameter of the tapered cylinder was defined by the diameter at 1/3 length from tip in consideration of the results of oscillation characteristics of tested cylinders. The cylinder with any taper ratio did not oscillated at Vr<1.0. The amplitude of the cylinder with any taper ratio was suppressed at less mass-damping parameter Cn than 2.5, which is the suppression criteria for in-line oscillation of 2-dimensional cylinder.(3)The publication "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 is certified to include the case of a cantilever-shaped cylinder with a finite span length. Less