Large Eddy Simulation of Circular Cylinder beneath the Water Surface

• Main Authors: Yu-An Lin, 林禹安
• Other Authors: Chia-Ren Chu
• Format: Others
• Language: en_US
• Published: 2017
• Online Access: http://ndltd.ncl.edu.tw/handle/4bg6pb

碩士 === 國立中央大學 === 土木工程學系 === 105 === The hydrodynamic loadings on the pipelines are essential parameters for pipeline design, especially when the pipelines are submerged in the river flow during flood events. This study focuses on the interaction between the free surface flow and a submerged cylinder with circular cross-section. This study integrates a Large Eddy Simulation (LES) model and the Volume of Fluid (VOF) method to examine the effect of free surface on the hydrodynamic loading of a submerged circular pipeline. The simulation results are verified by the results of flume experiments. Then the numerical model is utilized to investigate the influences of the Froude number, submergence ratio and blockage ratio on the flow field and the force coefficients of the circular cylinder. The simulation results reveal that the drag coefficient of the cylinder increases as the blockage ratio increases. When the Froude number FrD < 0.45, the water surface is smooth and undisturbed; when FrD > 0.68 and submergence ratio h* = 0.75, the water surface is elevated by the submerged cylinder and dropped behind the cylinder to create a forced jump. The simulation results indicate that the dynamic pressure on the upper side of the cylinder is affected by the water surface and the pressure distribution became asymmetric when the cylinder is very close to the water surface. This leads to the lift coefficient deviated from zero when the submergence ratio h*  2.0. The results of this study can be used for the structure design of submerged pipelines.