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波浪作用下直立结构物附近强湍动掺气流体运动的数值模拟

NUMERICAL SIMULATION OF THE HYDRODYNAMIC CHARACTERISTICS OF VIOLENT AERATED FLOWS NEAR VERTICAL STRUCTURE UNDER WAVE ACTION

  • 摘要: 波浪破碎卷入气体易对建筑物受力产生压力振荡, 了解波浪作用下建筑物附近掺气水流的运动特性是精确计算建筑物受力的前提. 基于OpenFOAM开源程序包和修正速度入口造波方法建立三维数值波浪水槽, 模型采用S-A IDDES湍流模型进行湍流封闭, 并采用修正的VOF 方法捕捉自由液面, 数值模拟了规则波在1:10的光滑斜坡上与直立结构物的相互作用过程, 重点分析了结构物附近的水动力和掺气水流运动特性. 结果表明, 建立的数值模型能精确地捕捉波浪作用下直立结构物附近的自由液面的变化以及气泡输运过程, 较好地描述气体卷入所形成的气腔形态以及多气腔之间的融合、分裂等过程; 波浪与直立结构物相互作用产生强湍动掺气水流, 其运动过程十分复杂; 掺气流体输运过程中水气界面周围一直伴随着涡的存在, 其中, 气泡的分裂与周围正负涡量剪切作用密切相关, 且其输运轨迹主要受周围流场的影响; 研究揭示了结构物附近湍动能与掺气特性的关系, 发现波浪作用下直立结构物附近湍动能的分布与掺气水流特征参数(气泡数量、空隙率)整体呈现一定的线性关系.

     

    Abstract: The air entrainment of water body under wave breaking is easy to produce pressure oscillation on the coastal structures. Therefore, in order to calculate the forces on the structures accurately, it is necessary to understand the motion characteristics of the aerated flows near coastal structure under wave action. In this study, a three-dimensional numerical wave flume is developed based on the OpenFOAM open source package together with the modified velocity inlet wave method. The model uses the S-A IDDES turbulence model to close the equations and the modified VOF method to capture the free surface. The interaction process of regular wave with a vertical structure on the smooth slope of 1:10 is simulated. Based on the comparison with the experimental results of the laboratory model, the hydrodynamic characteristics of violent aerated flows near the vertical structure are analyzed. The results show that the numerical model established in this study can accurately capture the space-time distribution of the free surface near the vertical structure and the transport process of bubbles under the action of regular waves. At the same time, the model can not only better describe the shape of the air cavity formed by the air entrainment, but also capture the process of merging and splitting among multiple cavities. The interaction between breaking waves and the vertical structure produces violent aerated flows, and its movement process is very complicated. The air-water interface is always accompanied by vortices in the wave propagation process. The bubble splitting in the air-water mixture is closely related to the positive and negative vortices. The transport trajectory of bubbles is mainly affected by the flow field around the bubbles. It is found that the distribution of turbulent kinetic energy in the vicinity of a vertical structure under the action of waves has a linear relationship with the characteristics of bubbles (bubble number, void fraction).

     

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