Wang Yi, Wang Yan, Cheng Zhe
National Engineering Laboratory for Pipeline Safety/MOE Key Laboratory of Petroleum Engineering/Beijing Key Laboratory of Urban Oil and Gas Distribution Technology, China University of Petroleum, Beijing 102249, China.
Institute of Naval Engineering Design, Naval Research Academy, Beijing 100070, China.
Polymers (Basel). 2019 Apr 2;11(4):596. doi: 10.3390/polym11040596.
Drag reduction by polymer is an important energy-saving technology, which can reduce pumping pressure or promote the flow rate of the pipelines transporting fluid. It has been widely applied to single-phase pipelines, such as oil pipelining, district heating systems, and firefighting. However, the engineering application of the drag reduction technology in two-phase flow systems has not been reported. The reason is an unrevealed complex mechanism of two-phase drag reduction and lack of numerical tools for mechanism study. Therefore, we aim to propose governing equations and numerical methods of direct numerical simulation (DNS) for two-phase gas-liquid drag-reducing flow and try to explain the reason for the two-phase drag reduction. Efficient interface tracking method-coupled volume-of-fluid and level set (VOSET) and typical polymer constitutive model Giesekus are combined in the momentum equation of the two-phase turbulent flow. Interface smoothing for conformation tensor induced by polymer is used to ensure numerical stability of the DNS. Special features and corresponding explanations of the two-phase gas-liquid drag-reducing flow are found based on DNS results. High shear in a high Reynolds number flow depresses the efficiency of the gas-liquid drag reduction, while a high concentration of polymer promotes the efficiency. To guarantee efficient drag reduction, it is better to use a high concentration of polymer drag-reducing agents (DRAs) for high shear flow.
聚合物减阻是一项重要的节能技术，它可以降低泵送压力或提高输送流体管道的流速。该技术已广泛应用于单相管道，如输油管道、区域供热系统和消防领域。然而，减阻技术在两相流系统中的工程应用尚未见报道。原因是两相减阻的复杂机制尚未揭示，且缺乏用于机理研究的数值工具。因此，我们旨在提出两相气液减阻流动的控制方程和直接数值模拟（DNS）的数值方法，并试图解释两相减阻的原因。在两相湍流的动量方程中，将高效的界面追踪方法——流体体积法和水平集法相结合（VOSET）以及典型的聚合物本构模型吉泽库斯模型。对聚合物引起的构象张量进行界面平滑处理，以确保DNS的数值稳定性。基于DNS结果，发现了两相气液减阻流动的特点及相应解释。高雷诺数流动中的高剪切力会降低气液减阻效率，而高浓度聚合物则会提高减阻效率。为保证高效减阻，对于高剪切流，最好使用高浓度的聚合物减阻剂（DRA）。
