Axial-Flow-Induced Vibration Of A Cylinder Cluster Under Different Incident Turbulent Intensities

Axial-flow-induced vibration is an important research direction in nuclear engineering.Fuel rods in a nuclear reactor are subjected to axial-flowing coolant fiercely,which leads to lateral vibration.The friction between fuel rods and spacer grid may wear fuel rods.In the present work,a silicon rubber cylinder is adopted to simulate fuel rod.Two configurations are studied;a twin-cylinder configuration and a 25-cylinder configuration which comprised of 1 flexible cylinder and 24 rigid cylinders.The influence of velocity gap ratio and turbulence intensity on cylinder’s dynamic behaviors are experimentally investigated.The experiments are conducted in a vertical water tunnel,the maximum velocity we can get is 2.13 m/s,and the corresponding natural turbulence intensity is about 0.7%.Flexible cylinder is made of silicon rubber,and has a length of 605 mm,and a diameter of 14 mm.The maximum non-dimensional velocity is 6.98.The cylinder is mounted both ends clamped-clamped firmly.LDV and FBG are adopted to measure vibration of the flexible cylinder.In the configuration of twin flexible cylinders,we use two LDV to measure two cylinders’ s vibration simultaneously,while in configuraion of 25 cylinders,two FBG are attached on the cylinder’s surface to measure vibrations of two directions.In addit ion,an active grid system is designed and tested in water tunnel.With the active grid installed upstream to the test section,the freestream turbulence intensity can be adjusted between 6% to 6.6% when velocity is 1.38 m/s.Detailed measurements on the flow field are also performed using PIV technique.For the twin-cylinder congiration,two cylinders’ vibration a re symmetrical,but correlation coeffic ient in two directions are very different.For 25-cylinder configuration,the vibration of flexible cylinder is diminished by small gap ratio.Physical mechanisms that responsible for the vibration characteristic are explained in this thesis.