基于CFD的海洋立管系统严重段塞流数值模拟

Numerical Simulation of Severe Slugging in Offshore Riser on CFD

利用CFD软件Fluent建立二维全尺寸仿真模型,对立管实验装置中的严重段塞流现象进行数值模拟研究。模拟方法中,采用液体体积函数(volume of fluid,VOF)法追踪气液界面;将长距离海底管道等效为箱体,以提高计算效率。模拟出了立管系统中的四种流型:典型严重段塞流(SSI)、严重段塞流II(SSII)、过渡流型(SST)和稳定流动;并对这四种流型的模拟结果进行了实验验证。最后,对典型严重段塞流的瞬态流动特性进行了深入分析。结果表明:采用数值模拟方法计算效率高,可准确模拟严重段塞流现象,为长距离立管系统中严重段塞流研究提供了切实可行的模拟方法。模拟工况下,气液喷发的瞬时质量流量可达入口的2.5倍以上,气液平均流速可达入口的4.5倍以上,其瞬态流动特性的分析对严重段塞流危害的准确评估有重要意义。

A 2D CFD model for the full size experimental facility was developed,and the severe slugging phenomena under different conditions were numerically simulated to study the transient characteristics of severe slugging by using Fluent. In the simulations,the VOF method was adopted to track the gas-liquid interface,and the long subsea pipeline was equivalent as a tank to improve calculating efficiency. Four flow patterns were numerically simulated including typical severe slugging（ SSI）,severe slugging II（ SSII）,transition to severe slugging（ SST）and stable flow. The simulation results of the four flow patterns were compared with the experimental data. Finally,the transient characteristics of the typical severe slugging were analyzed thoroughly. The results show that the present numerical simulation methods can be used to simulate the severe slugging phenomena accurately and these methods are reasonable for the simulation of severe slugging in long riser system. Under the present condition,the maximum instantaneous mass flow rate can reach the 2. 5 times of the inlet,and the instantaneous average flow velocity can reach 4. 5 times of the inlet liquid velocity. These analyses have important implications for the hazard assessment of severe slugging.