基于格子玻尔兹曼方法的双液滴撞击壁面液膜的热特性演化过程

为了研究并排双液滴撞击覆有液膜的高温壁面过程中壁面热流密度分布特征,基于水热耦合双分布函数格子玻尔兹曼伪势模型,探究了液滴间距、撞击速度和液相黏滞系数在不同时刻对壁面瞬时热流密度分布的影响。结果表明：低温液滴的扩散与下潜导致撞击区和中心射流区的壁面与液膜之间的温度梯度上升,引起撞击区和中心射流区壁面热流密度骤增。撞击区传热形式以对流传热为主,静态区受液冠处速度不连续性影响,其传热形式以扩散传热为主。双液滴撞击速度增大导致液滴下潜和扩展程度加深,液膜内部对流传热增强。双液滴间距增加引起双液滴内侧液冠在液膜内扩展空间增大,造成瞬时壁面高热流密度区域面积增加,利于散热。此外,更大的液相黏滞系数增大了液滴撞击液膜过程中的黏滞耗散,降低低温液滴的下潜程度和撞击区的液膜流场对流强度,导致壁面热流密度峰值减小。

Study on the Evolution Process of Thermal Properties of Liquid Film Impinged by Double Droplet Based on Lattice Boltzmann Method

In order to investigate the characteristics of wall heat flow density distribution in the process of side-by-side double droplets impinging on the high temperature wall covered with liquid film, the effects of droplet spacing, impact velocity and liquid phase viscosity coefficient on the instantaneous wall heat flow density distribution at different moments were investigated based on the lattice Boltzmann pseudopotential model with hydrothermal coupling double distribution functions. The results show that the diffusion and dive of low-temperature droplets lead to an increase in the temperature gradient between the wall and liquid film in the impact zone and the central jet zone, causing a sharp increase in the heat flow density of the wall in the impact zone and the central jet zone. The heat transfer in the impact zone is mainly in the form of convective heat transfer, and the heat transfer in the static zone is mainly in the form of diffusive heat transfer due to the effect of velocity discontinuity at the liquid crown. The increase of double droplets impact velocity leads to the deepening of droplet dive and expansion, and the convective heat transfer inside the liquid film is enhanced. The increase of double droplets spacing causes the expansion space of the liquid crown inside the liquid film to increase, resulting in the increasing area of high heat flow density region on the transient wall surface, which is conducive to heat dissipation. In addition, the larger viscosity coefficient of the liquid phase increases the viscous dissipation during the droplet impact with the liquid film, which reduces the dive of the low-temperature droplet and the convection intensity of the liquid film flow field in the impact area, and leads to the reduction of the peak heat flow density at the wall surface.