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Ekman boundary layer mass transfer mechanism of free sink vortex
International Journal of Heat and Mass Transfer ( IF 5.2 ) Pub Date : 2020-04-01 , DOI: 10.1016/j.ijheatmasstransfer.2019.119250
Dapeng Tan , Lin Li , Zichao Yin , Daifeng Li , Yinlong Zhu , Shuai Zheng

Abstract The suction-extraction phenomenon occurs in the formation process of free sink vortex, and it is a complex gas-liquid coupling matter. The mass transfer mechanism of the Ekman boundary layer involved in the above matter is with important scientific value and engineering significance. To address the matters, we construct a Rankine-vortex-based fluid mechanic model, and propose a Helmholtz-equation-based solution method to acquire the critical penetration condition of sink vortex. The two-phase mass suction-extraction mechanism of the Ekman boundary layer is discussed. Then, a coupled computational fluid dynamic and discrete element method (CFD-DEM) modeling method is presented to obtain the matter transfer regularities of particles pumped by sink vortex, and the critical condition of particle stability motion is solved by the Laplace transform method. Numerical results show that the critical penetration condition is a data set because of different initial velocity components; the heights of suction/extraction holes form the container bottom have no relation to the initial velocity components; if the initial disturbances are enhanced, the suction-extraction height and Ekman layer thickness increase, but the Ekman suction-extraction intensities grow weaker; a particle aggregation phenomenon exists in the vortex center, and can be stable state until the surface tension broken by the Ekman suction effect, wherein the Ekman resultant force with different positions causes the particle motion trajectory to be complex. A PIV observation experimental platform is developed, and the effectiveness of the proposed method is verified. Then, the vortex core boundary is observed, so the radius of the vortex core can be acquired precisely; there is an energy transition process from potential energy to kinetic energy in the suction and extraction stages, which causes the Ekman boundary vorticity intensities to decline; the particle pumping process induces the aggregation and dissipation of turbulent vortices quickly, accelerating the fluid mass transfer efficiencies. The research works can provide direct guidance for the active control of vortex formation in industrial areas, and supply useful references to related fluids engineering calculation issues.

中文翻译:

自由汇涡的 Ekman 边界层传质机制

摘要 自由汇涡形成过程中会发生吸-抽现象,是一种复杂的气液耦合物质。上述涉及的埃克曼边界层的传质机制具有重要的科学价值和工程意义。针对这一问题,我们构建了基于Rankine-涡旋的流体力学模型,并提出了一种基于亥姆霍兹方程的求解方法来获取汇涡的临界穿透条件。讨论了埃克曼边界层的两相质量吸-抽机制。然后,提出了一种耦合计算流体动力学和离散元法(CFD-DEM)建模方法,以获得由汇涡泵送的粒子的物质传递规律,用拉普拉斯变换方法求解粒子稳定运动的临界条件。数值结果表明,由于初始速度分量不同,临界穿透条件是一个数据集;容器底部的抽吸孔高度与初速分量无关;如果初始扰动增强,吸-抽高度和Ekman层厚度增加,但Ekman吸-抽强度变弱;涡流中心存在粒子聚集现象,在Ekman吸力作用打破表面张力之前可以保持稳定状态,其中不同位置的Ekman合力导致粒子运动轨迹复杂。研制了PIV观测实验平台,并验证了所提方法的有效性。然后观察涡核边界,从而精确获取涡核半径;抽吸阶段存在势能向动能的能量转换过程,导致埃克曼边界涡度强度下降;粒子泵送过程会迅速引起湍流涡流的聚集和消散,从而加快流体传质效率。研究工作可为工业领域涡形成的主动控制提供直接指导,并为相关流体工程计算问题提供有益参考。抽吸阶段存在势能向动能的能量转换过程,导致埃克曼边界涡度强度下降;粒子泵送过程会迅速引起湍流涡流的聚集和消散,从而加快流体传质效率。研究工作可为工业领域涡形成的主动控制提供直接指导,并为相关流体工程计算问题提供有益参考。抽吸阶段存在势能向动能的能量转换过程,导致埃克曼边界涡度强度下降;粒子泵送过程会迅速引起湍流涡流的聚集和消散,从而加快流体传质效率。研究工作可为工业领域涡形成的主动控制提供直接指导,并为相关流体工程计算问题提供有益参考。
更新日期:2020-04-01
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