Experimental Study On Axial Flow Induced Vibration Of Cylinder

The thesis mainly concerns the experimental study of axial flow induced vibration of one flexible cylinder in both laminar and turbulent flow. A silicone rubber cylinder with specific elasticity modulus was developed as the model, and a turbulent grid was designed to generate homogeneous and isotropic turbulence flow.The experiments were performed in the newly built water tunnel, so firstly the performance documentation was performed. Mean flow velocity was measured in the range of 0.05 ~ 0.24 m/s, and turbulent intensity was about 0.3%. The amplitude of tunnel wall vibration was within 5 μm in all velocity range, and the spectrum indicates the vibration was more a like random one with prominent peaks around 10 Hz. Boundary layer thickness in center of test section reduced from 29 to 22 mm as flow velocity increases. The water temperature fluctuation was within 0.1 degree and gets stable after 2 hours preheating, with a negligible influence on experiment.Axial flow induced vibration of cylinder was studied systematically. The max non-dimensional flow velocity and Reynolds number based on diameter can reach 7.07 and 5.6 × 104. Firstly, the effect of water tunnel vibration on cylinder was verified and said to be neglected in both amplitude and PSD perspectives when velocity gets over 0.1 m/s. The amplitude will increase as flow velocity or turbulent intensity increases. Vibration modal character was verified can be decomposed into three modes. The mechanism of bucking was studied by decomposing amplitude into mean and RMS amplitudes. It was found the axial load from skin friction on cylinder caused buckling. Turbulent intensity of incident flow cannot enhance the onset of buckling, but induces significant pressure fluctuation on cylinder wall which leads to larger RMS vibration amplitude. The mechanisms of subcritical vibration were studied through the analysis of flow field, pressure and flow visualization technique.