Submarine piggyback pipeline is an important tool for oil and gas transport, especially, in the marginal oil field. When the scour happens in the seabed, the pipeline slides easily, which may cause the pipeline failure. The dynamic slope angle is one of the most important characteristics of the scour. In this work, the dynamic slope angles of the sandy seabed under piggyback pipelines in steady flow are investigated experimentally and numerically in detail. The physical experiments are conducted in an annular flume and the numerical simulations are carried out using a two-phase flow model which is resolved by the finite volume method (FVM). In the numerical model, the free surface is tracked by the volume of fluid (VOF), and both bed and suspended loads are considered in the scour module. Depending on the comparison and convergence analysis, the numerical results are in good agreement with the experimental results. The results indicate that the dynamic slope angle is significantly affected by the incoming flow velocity, gap-ratio, spacing-ratio and pipe diameter. With the reduction of gap-ratio and space-ratio, the upstream dynamic slope angle α increases slightly, but the downstream dynamic slope angle β decreases. With the increase of the grain Reynolds number, the angle α increases slightly, but the angle β decreases severely. The conclusions drawn from this paper could provide the reference for the design of submarine piggyback pipeline.

海底背负式管道是油气输送的重要工具，尤其是在边缘油田。当冲刷发生在海底时，管道容易滑动，可能导致管道故障。动态倾斜角是冲刷最重要的特性之一。在这项工作中，通过实验和数值详细研究了稳定流中背负式管道下沙质海床的动态倾斜角。物理实验在环形水槽中进行，数值模拟是使用由有限体积法 (FVM) 解析的两相流模型进行的。在数值模型中，自由表面由流体体积 (VOF) 跟踪，并且在冲刷模块中考虑了床和悬浮载荷。根据比较和收敛分析，数值结果与实验结果吻合良好。结果表明，动态坡角受来流速度、间隙比、间距比和管径的显着影响。随着间隙比和空间比的减小，上游动力坡角α略有增加，但下游动力坡角β减小。随着晶粒雷诺数的增加，角度α略有增加，但角度β急剧减小。本文得出的结论可为海底背负式管道的设计提供参考。