电场作用下气泡上升行为特性的数值计算研究

利用电场控制气泡形态及运动,强化气液相间传热传质是电流体动力学的重要研究内容之一. 然而目前多数研究集中在非电场下的气泡动力学上,对于电场下的气泡行为特性及电场的作用机制仍需开展深入研究. 本研究对电场作用下单个气泡在流体中上升过程的动力学行为进行了数值模拟研究. 在建立二维模型的基础上求解电场方程与Navier-Stokes方程,并采用水平集方法捕捉了上升气泡的位置及形状. 模拟结果的准确性与有效性通过与前人实验和数值结果进行对比得到了验证. 通过改变雷诺数、邦德数和电邦德数等不同参数研究了电场下液体黏度、表面张力和电场力对气泡运动变形的影响. 计算结果表明,电场对气泡的动态特性有显著影响. 非电场情况下液体黏度和表面张力较大时气泡基本维持球状,反之气泡发生变形并逐步达到稳定状态. 此外,电场作用使气泡在初始上升阶段发生剧烈形变,随着不断上升,气泡形变程度不断减小,且气泡的上升速度和长径比均出现振荡. 垂直电场使气泡的上升速度有较大的提高,且随着电邦德数的增大,难以达到相对稳定的状态. 

NUMERICAL SIMULATION ON BUBBLE RINSING BEHAVIORS UNDER ELECTRIC FIELD 1)

Employing an electric field to control bubble morphology and motion, and enhance heat and mass transfer between gas and liquid are one of the important research contents of electrohydrodynamics (EHD). However, most of the current researches focus on the dynamics of bubbles under non-electric fields. Further research is needed on the behaviors of bubbles and the mechanism of electric fields under electric fields. In the present study, the dynamic behaviors of a single bubble rising in a fluid under an external electric field are numerically simulated. Based on the model established on two-dimensional, the equation of electric field and Navier-Stokes are solved, and the level set method is used to accurately capture the position and morphology of the rising bubble. The accuracy and validity of the present simulation results are verified by comparing with previous experiments and numerical results. The effects of liquid viscosity, surface tension and electric field force on bubble motion and deformation under electric field are examined by employing the Reynolds ($Re$), Bond ($Bo$) and electrical bond ($Bo_{\rm e}$) numbers. The calculation results show that the electric field has a significant influence on the dynamic characteristics of the bubble. In the case of a non-electric field, the bubble basically maintains a spherical shape when the viscosity of the liquid and the surface tension are large. Instead, the bubbles deform and gradually reach a steady state. Additionally, the bubble is strongly deformed at the initial rising stage by attributing to the electric field. With the bubble further rising, the deformation weakened, and both of the bubble velocity and aspect ratio are oscillated. The effect of vertical electric field causes a greater increase in the velocity of rising bubble. As the number of $Bo_{\rm e}$ increases, the bubble has an intense oscillation, making it more difficult to achieve a relatively stable state.