蒸发液滴内部非稳态流动的数值计算

在气液两相流VOF(volume of fluid,VOF)模型的基础上耦合CSF(continuum surface force,CSF)表面张力模型,建立了高温平板上的铺展液滴与高温空气中悬浮液滴蒸发过程中内部非稳态流动模型,对液滴蒸发过程中内部非稳态流动进行了研究。基于相变理论,采用用户自定义函数将流体相变模型加入非稳态流动模型中进行耦合计算,获得了高温平板上的铺展液滴与高温空气中悬浮液滴蒸发过程中的内部流动及变化过程。液滴蒸发过程中非稳态内部流动由液滴表面的温度梯度引发,Marangoni流动在液滴内部形成的时间非常短,流体从液滴表面高温区域流向低温区域。计算结果表明:高温平板上随着液滴蒸发的进行,液滴内部一直保持两个对称的涡流,Marangoni流动比较稳定;高温空气环境中随着液滴蒸发的进行,液滴内部四个涡流逐渐转变成两个对称的涡流;液滴内部温度分布因Marangoni流动加强传热而变得均匀,同时由于温度分布变得均匀,Marangoni流动被削弱。

Numerical study on transient flow in evaporating droplet

The numerical simulation of the unsteady flow in the Evaporating droplet on the heated plate and the droplet evaporation suspending in high temperature air was carried out. The Navier-Stokes equations expressing the flow distribution of the liquid and gas phases, coupled with the Volume of Fluid method (VOF) to track the liquid-gas interface, combined Continuum Surface Force (CSF) model to calculate the surface tension, are numerically solved using the finite volume methodology. An evaporation model coupled with VOF methodology predicts the evaporating rates for a droplet with internal circulation and stagnation flow, respectively. The CSF model combined VOF methodology predicts the formed processes of unsteady internal flow. Unsteady internal flow would be induced by temperature gradient at droplet surface .The flow is generated from higher temperature to lower surface domains, and Marangoni flow inside the droplet is formed in short time. Evaporation of droplet on the plate is numerically carried out, the inner of the droplet has been kept two symmetric vortexes, and the Marangoni flow is relatively stable. For the suspending droplet, four vortexes converted into double axisymmetric vortexes with evaporating. The temperature distributions inside the droplet become uniform due to existence of Marangoni flow, and the heat transfer would be enhanced. To the contrary, Marangoni flow would be weakened due to uniform temperature distribution.