水滴撞击运动超疏水表面特性及其调控研究

Research on the characteristics of water droplets impacting moving superhydrophobic surfaces and its regulation

  • 摘要: 结冰给航空安全带来了重大挑战,超疏水表面可通过使撞击壁面的水滴回弹脱离进而实现防冰,受到了广泛关注。风力机、飞行器等装备发生结冰时,水滴粒径大多为微米至数十微米,壁面往往处于运动状态,而微米级水滴撞击运动超疏水表面的特性尚缺乏实验研究。本文设计了微米级水滴撞击运动超疏水表面实验台,通过高速摄影发现微米级水滴撞击超疏水表面的接触时间会在表面切向速度较高时显著增大(78%),与毫米级水滴的结果相反。进一步地,通过数值模拟深入分析了水滴撞击运动超疏水表面的过程,揭示了壁面运动对水滴撞击特性的影响。除了使水滴整体向壁面运动方向移动之外,壁面运动对微米级水滴撞击运动超疏水表面的影响主要有三个方面:分别为延长质心下降过程、将水滴质量从展向向流向转移,以及改变水滴铺展及回缩特性。并分析出超疏水表面高速运动对微米级水滴接触时间的延长是由于其对水滴前缘的剧烈拉伸导致的。随后,并通过对水滴施加合成双射流降低了水滴与壁面之间的切向相对撞击速度,将接触时间降低了28%。

     

    Abstract: Icing poses significant hazards to aviation safety. Superhydrophobic surfaces have gained widespread attention for their capability to induce rebounding and detachment of impacting water droplets from surfaces, thereby achieving anti-icing. When icing occurs on equipment such as wind turbines and aircraft, the droplet diameter typically ranges from micrometers to tens of micrometers, and the surface is often in motion. However, experimental research on the characteristics of micrometer-scale water droplets impacting moving superhydrophobic surfaces remains vacant. Consequently, in this paper, we developed an experimental platform to investigate the impact of micron-sized water droplets on moving superhydrophobic surfaces. High-speed photography revealed that, contrary to observations with millimeter-scale droplets, the contact time of micrometer-scale water droplets impacting superhydrophobic surfaces increases significantly (by 78%) at high surface tangential velocities. Furthermore, numerical simulations were conducted to gain deeper insights into the impact process, particularly focusing on the influence of surface motion on the impact characteristics of water droplets. This influence mainly manifests in three aspects: it prolongs the centroid descent process, redirects water droplets from the expansion direction to the flow direction, and changes the expansion and retraction characteristics of water droplets. The extension of the contact time of micrometer-scale water droplets due to the high-speed motion of superhydrophobic surfaces is attributed to the intense stretching of the water droplets' front edge. Subsequently, by applying dual synthetic jets to water droplets, the tangential relative impact velocity between the droplets and the surface is decreased, resulting in a 28% reduction in the contact time.

     

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