NOZZLE JET FLOW-INDUCED VIBRATION OF SINGLE CIRCULAR-CYLINDERS AND TWIN CIRCULAR-CYLINDERS

This study is an experimental investigation of the vibration phenomena of circular cylinders installed in a tube when they are subject to a cross-flow discharged through a nozzle hole of the outer tube. The objectives of this study are (1) to clarify the flow-induced vibration phenomena of the circular cylinders, (2) to obtain vortex shedding frequencies, (frequencies of the fluid-exciting forces acting on the circular cylinders), and (3) to obtain the design data for circular cylindrical structures. Thermowells are an example of this arrangement and are used as protective tubes for temperature measurement of fluid flowing in the piping and so on in power plants. Two types of models were used for the flow tests carried out in a water loop: a single circular cylinder and twin circular cylinders. The tests were carried out with nozzle outlet flow velocities ranging from 5 m/s to 20 m/s. The vibrations of the cylinders at each flow velocity were measured with an accelerometer mounted inside the cylinder. As the results of the tests, the following points have been clarified: (1) The circular cylinder presents a resonance phenomenon in which the amplitude increases in a certain nozzle flow velocity range. (2) The Strouhal numbers defined on the basis of the nozzle diameter and the resonance flow velocity are 0.5 to 0.56 (0.24 to 0.29) for the single circular cylinders and are 0.34 to 0.4 for the twin circular cylinders.