低温壁面液滴撞壁的飞溅特性及铺展机理研究

Study of splash characteristics and spreading mechanism of liquid droplets impacting walls at low temperature

  • 摘要: 液滴撞击低温壁面是导致飞机机翼结冰、电线覆冰以及内燃机冷起动性能恶化的重要因素之一,其中液滴的飞溅和铺展是引发上述问题的关键原因。为此,本文采用高速摄影法,对正十二烷液滴撞击不同温度铝板时的飞溅和铺展特性进行了系统的试验研究。结果表明:壁面温度从20 ℃降至–40 ℃,液滴破碎阈值明显降低,二次液滴的直径显著增大和数量显著增多,而附壁液膜的铺展速度和最大铺展距离则明显减小。本研究针对附壁液膜在低温壁面快速铺展阶段的运动学特征,考虑了壁面温度对黏性力的影响,建立了新的无量纲铺展因子,并提出新的铺展模型。该模型不仅能准确描述不同入射条件下的液膜铺展过程,还将传统铺展模型的适用范围从0.1~1.0拓宽至0.1~1.5,从而能准确地反映液膜在更长时间内的铺展规律变化。

     

    Abstract: The phenomenon of droplets impacting on the cold wall is one of the key factors leading to the deterioration of aircraft wing icing, wire icing and cold start of internal combustion engine. Droplet splashing and spreading characteristics are the main causes of the above problems. High-speed photography was used to study the splashing and spreading characteristics of n-dodecane droplets striking aluminium plates at different temperatures. The results show that as the wall temperature decreased (20 ℃ to −40 ℃) the droplet fragmentation threshold is significantly reduced, the secondary droplet diameter and number increase significantly, and the spreading speed and maximum spreading distance of the attached liquid film decrease significantly. In this study, a new dimensionless spreading coefficient and a new spreading model were constructed for the kinematic characteristics of the fast spreading phase of the liquid film attached to the low temperature wall, considering the effect of wall temperature on the viscous forces. The spreading model not only enables an accurate description of the liquid film spreading process under different insertion conditions and wall temperatures, but also widens the range of application of the model from 0.1–1.0 to 0.1–1.5, allowing the resulting low temperature spreading model to accurately describe changes in the spreading pattern of the liquid film over a longer period of time.

     

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