黏性对液滴偏心撞击旋转壁面铺展特性的影响

Effect of liquid viscosity on droplet spreading after off⁃axis impacton rotating wall

液滴撞击旋转壁面广泛存在于工程实践中,如在航空领域发生的发动机吸雨吸冰现象,这些现象会导致发动机性能下降甚至引发安全问题,因此研究液滴撞击旋转壁面具有重要意义。搭建并开展液滴撞击旋转圆盘实验并用高速相机采集图像,在保持液滴尺寸、撞击速度、表面张力和撞击位置不变的情况下,研究了转速和黏性对液滴偏心撞击后铺展规律的影响。通过后处理液滴铺展动态图片,定量获取液滴沿径向和切向铺展数据。实验结果表明,液滴径向-切向铺展动态模式在旋转邦德数和旋转雷诺数下划分出4个区域:撞击惯性力-黏附力、撞击惯性力-黏附力/黏滞力过渡、撞击惯性力/离心力过渡-黏附力、撞击惯性力-黏滞力。径向上撞击惯性力主导模式下,最大径向铺展因子随奥内佐格数和旋转邦德数增大而减小,且在回缩阶段径向铺展因子与无量纲时间t/(Oh·T)满足−1/3幂次标度律。切向上黏附力主导模式下,液滴切向铺展速率与无量纲时间t/(Oh·T)满足2/3幂次标度律;切向上黏滞力主导模式下,切向铺展存在最大铺展因子。

Droplet impact on the rotating wall widely exists in the engineering field,such as rain ingestion and ice ac⁃cretion occurring on aircraft engines,which will lead to efficiency loss and even safety problems.Therefore,it is of great significance to study the impact of liquid droplets on the rotating wall.An experimental set-up of droplet impacting on a rotating disc is built and experiments are conducted and recorded with a high-speed camera.The effects of the rotating speed and viscosity on the droplet spreading after off-axis impact are studied while the droplet size,impact ve⁃locity,surface tension and impact position remain unchanged.The evolution of droplet diameter data along the radial and tangential directions was quantitatively obtained by post-processing the recoded images.The experimental results show that the radial-tangential spreading dynamic follows four different regimes with the rotational Bond number and ro⁃tational Reynolds number:impact inertia force-adhesion force,impact inertia force-adhesion force/viscous force transi⁃tion,impact inertia force/centrifugal force transition-adhesion force,and impact inertia force-viscous force.In the im⁃pact inertial force dominant regime for the radial spreading,the maximum radial spreading factor decreases with the Ohnesorge number and the rotational Bond number,and the radial spreading factor evolves with the dimensionless time t(/Oh·T)by a−1/3 pow-law.In the tangential adhesion force dominant regime,the tangential spreading rate of droplets exhibits a 2/3 pow-law with the dimensionless time t(/Oh·T).In the tangential viscosity force dominant mode,maximal spreading factors are reached in the tangential direction.