Borthakur Manash Pratim, Biswas Gautam, Bandyopadhyay Dipankar
Department of Mechanical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India.
Department of Chemical Engineering, Indian Institute of Technology Guwahati, Guwahati 781039, India.
Phys Rev E. 2017 Jul;96(1-1):013115. doi: 10.1103/PhysRevE.96.013115. Epub 2017 Jul 25.
This paper presents a numerical investigation of the dynamics of pinch-off in liquid drops and jets during injection of a liquid through an orifice into another fluid. The current study is carried out by solving axisymmetric Navier-Stokes equations and the interface is captured using a coupled level-set and volume-of-fluid approach. The delicate interplay of inertia and viscous effects plays a crucial role in deciding the dynamics of the formation as well as breakup of liquid drops and jets. In the dripping regime, the growth and breakup rate of a drop are studied and quantified by corroborating with theoretical predictions. During the growth stage of the drops, a self-similar behavior of the drop profile is identified over a relatively short duration of time. The viscosity of the drop liquid shows substantial influence on the thinning behavior of a liquid neck and a transition is observed from an inertia dominated regime to an inertia-viscous regime beyond a critical minimum value of the neck radius. The phenomenon of interface overturning is fundamentally related to the magnitude of drop viscosity. The variation of overturning angle as a function of drop viscosity is computed and a critical value of Ohnesorge number is obtained beyond which overturning ceases. Increasing the inertia of drop liquid transforms the system from a periodically dripping regime to a quasiperiodic regime and finally it culminates into an elongated liquid jet. Another interesting transition from dripping to jetting regime is demonstrated by varying the viscosity of the ambient medium. The breakup of jets in Rayleigh mode is explored and the breakup length obtained from our computations shows excellent agreement with the theoretical predictions owing to Rayleigh's analysis. The ambient medium is entrained as the jet moves downstream with the creation of a vortical structure just outside the jet signifying increased participation of the ambient medium in the dynamics of jet breakup at higher inflow rates.
本文对通过孔口向另一种流体中注入液体时液滴和液柱的 pinch-off 动力学进行了数值研究。当前的研究通过求解轴对称的 Navier-Stokes 方程来进行，并且使用耦合水平集和流体体积方法来捕获界面。惯性和粘性效应之间微妙的相互作用在决定液滴和液柱的形成以及破裂动力学方面起着至关重要的作用。在滴状流态下，通过与理论预测进行对比，研究并量化了液滴的生长和破裂速率。在液滴的生长阶段，在相对较短的时间内识别出了液滴轮廓的自相似行为。液滴液体的粘度对液柱变细行为有显著影响，并且观察到从惯性主导区域到颈部半径临界最小值以上的惯性-粘性区域的转变。界面翻转现象从根本上与液滴粘度的大小有关。计算了翻转角度随液滴粘度的变化，并获得了 Ohnesorge 数的临界值，超过该值翻转停止。增加液滴液体的惯性会使系统从周期性滴状流态转变为准周期性流态，最终 culminates 为细长的液柱。通过改变周围介质的粘度，展示了从滴状到射流流态的另一个有趣转变。探索了瑞利模式下液柱的破裂，并且由于瑞利分析，我们计算得到的破裂长度与理论预测显示出极好的一致性。随着液柱向下游移动，周围介质被夹带，在液柱外部形成了一个涡旋结构，这表明在较高流入速率下周围介质更多地参与了液柱破裂的动力学过程。
