Local scour around two pipelines in tandem in steady current
Local scour around two pipelines in tandem in steady current
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DOI：
10.1016/j.coastaleng.2015.01.001
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发表时间：
2015-04
影响因子：
4.4
通讯作者：
Mingde Zhao;Shailesh Vaidya;Qin Zhang;Liang Cheng;Liang Cheng
中科院分区：
文献类型：
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作者：
Mingde Zhao;Shailesh Vaidya;Qin Zhang;Liang Cheng;Liang Cheng
在这项研究中，局部冲刷周围的两个相同的管道在串联布置的数值研究。采用二维雷诺平均Navier-Stokes（RANS）方程，结合泥沙质量守恒方程，模拟了两条管道的绕流和管道下方局部冲刷剖面的演变。两个管道之间的差距比（G/D）的范围为0.5至5，间隔为0.5，其中G是两个管道之间的差距，D是管道的直径。研究的重点是探讨差距比对冲刷深度和冲刷时间尺度的影响。结果表明，在清水和动床条件下，下游管道下方的冲刷深度均大于上游管道下方的冲刷深度，这是由于上游管道的旋涡脱落作用造成的。在清水和活床条件下，下游管道下方的最大冲刷深度发生在G/D= 2.5处，这大约是上游管道发生旋涡脱落的临界间隙比。当差距比大于2.5时，上游管道的旋涡脱落对下游管道冲刷的影响减弱，下游管道下方的冲刷深度随间隙比的增大而减小。清水条件下的冲刷是在比活床冲刷临界流速低25%的流速下模拟的。清水和动床条件下，两条管道下方冲刷深度的变化规律相似。在冲刷过程中，下游管道上出现了较强的正平均升力系数，这对下游管道的稳定性有不利影响。当上游管道发生旋涡脱落时，下游管道上的均方根升力系数显著增大。
In this study, local scour around two identical pipelines in a tandem arrangement are investigated numerically. The two-dimensional Reynolds-averaged Navier–Stokes (RANS) equations, together with the conservation equation of the sediment mass are solved to simulate the flow around two pipelines and the evolution of the local scour profile below the pipelines. The gap ratios between the two pipelines (G/D) range from 0.5 to 5 with an interval of 0.5, whereGis the gap between the two pipelines andDis the diameter of the pipelines. The focus of the study is to investigate the effects of the gap ratio on the scour depth and scour time scale. It is found that the scour depth below the downstream pipeline is greater than that below the upstream pipeline under both clear water and live bed conditions because of the effect of the vortex shedding from the upstream pipeline. The maximum scour depth below the downstream pipeline occurs atG/D= 2.5 under both clear water and live bed conditions, which is about the critical gap ratio beyond which vortex shedding from the upstream pipeline occurs. As the gap ratio exceeds 2.5, the scour depth below the downstream pipeline decreases with increasing gap ratio due to the weakening effect of the vortex shedding from the upstream pipeline on the scour. The scour under the clear water condition is simulated at a velocity 25% lower than the critical velocity for live bed scour. The variations of the scour depths below the two pipelines in the clear water and live bed conditions are found to be similar to each other. Strong positive mean lift coefficient on the downstream pipeline was observed during the scour process, which is believed to have a negative effect on the stability of downstream pipeline. The RMS lift coefficient on the downstream pipeline increases significantly when the vortex shedding from the upstream pipeline occurs.