海底管道悬跨段的近壁圆柱绕流分析

海底管道靠近海床表面处受海流冲刷,管道与海床表面产生一定间隙,该间隙与管道直径的比值定义为间隙比。通过数值模拟和物理模型试验,研究间隙比对管道绕流的水动力特性的影响。物理模型试验中,六分力天平测得管道的阻力和升力,数值模拟研究管道尾流流态和旋涡发放频率。结果表明:间隙比低于某临界值时,海床的存在阻碍了剪切层与层外流动间的相互作用,抑制层内涡量的传递,下游旋涡得不到充分发展,发放频率有所降低;海床壁面加剧管道两侧压力分布不均匀,压力差增加,因而管道阻力和升力增大;间隙比高于某临界值时,海床的抑制作用逐渐削弱,旋涡脱落趋于规则,海床未对绕流产生较大影响,管道受力随之趋于稳定。该研究可为海流冲刷引起的海底管道悬跨现象的安全设计提供理论指导。

Analysis of Submarine Pipeline Suspended Problemsby Flow around a Near Wall Cylinder

The pipeline near the seabed is washed by the current. There is a certain gap between the pipeline and the seabed surface. The ratio between the gap G and the diameter of the pipeline D is defined as the gap ratio e. Through the numerical and experimental approaches, the influence of gap ratio on the hydrodynamic characteristics of pipe flow around the pipe is studied. In the physical model experiment, the six-component force transducer is used to measure the drag and lift of the pipe. The flow state of the pipeline and the frequency of the vortex distribution were simulated by numerical simulation. The results show that when the gap ratio is lower than a critical value, dynamic interaction between the shear layers and outflow is hampered by the seabed, transfer of vorticity within layer is inhibited, the downstream vortex is not fully developed, and firing frequency is reduced; the pressure distribution on both sides of seabed pipeline is uneven, pressure difference increases, thus the drag and lift of pipeline increases. When the gap ratio is higher than a critical value, the inhibition effect of the seabed gradually weakens, and the vortex shedding tends to be regular. The seabed does not have a great influence on the flow around the seabed, and the stress of the pipeline tends to be stable. The study provides theoretical guidance for the safety design of submarine pipeline suspension caused by the scour of sea current.