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采用耦合水平集-体积分数法并综合考虑传热及接触热阻作用建立了中空液滴碰撞水平壁面数值模型，并验证了模型的可靠性.通过分析计算结果，获得了中空液滴与实心液滴撞壁的动力学特征差异，揭示了中空液滴撞壁流动传热机理和中心射流形成机制，探索了碰撞速度和壁面浸润性对中空液滴撞壁动力学和传热特性的影响.研究表明：中空液滴撞壁后中心射流特征明显，并伴随有射流收缩和液壳破碎等现象.中空液滴内部压力梯度是液滴铺展、中心射流产生和发展的主要原因；撞壁过程中中心射流表面温度分布较为均匀，破碎液壳表面温度分布波动较大.碰撞速度与中空液滴撞壁最大铺展系数的相关性较小，但其对无量纲射流长度和壁面平均热流密度的影响较大；壁面浸润性与中空液滴撞壁后期铺展系数的相关性较大，但其对无量纲射流长度和壁面平均热流密度的影响较小.Many researches of a dense droplet impacting on a flat surface have been reported in the literature. However, the mechanism of a hollow droplet impacting on a flat surface has not yet been well addressed. A mathematical model is developed in the present research to resolve this impacting process. The model couples level set and volume of fluid method, and considers heat transfer and contact resistance between the droplet and surface. The validation of the model is carried out by comparing simulation results with experiment data. Different impact behaviors are observed in the impacting processes of both the dense droplet and the hollow droplet on a flat surface, obtained from the simulation result. The hydrodynamics and heat transfer behaviors of the hollow droplet impacting on a flat surface and the formation of central jetting are also explored. The effects of impact velocity and surface wettability on the impacting behavior of the hollow droplet are also analyzed. The results show that in the impacting process, the hollow droplet presents a spread and central jetting pattern, accompanying liquid shell contraction and breakup, while only spread and liquid shell contraction are observed in the dense droplet impacting process. It is also observed that the central jetting of the hollow droplet peels off the surface in the final impacting stage. The dimensionless spread factor for the hollow droplet is less than that of the dense droplet with the same initial kinetic energy in spread stage. The pressure gradient inside the hollow droplet is the main factor resulting in the spread and central jetting. The temperature distribution in the liquid shell and the surface is more uniform than in the central jetting, which is caused by the secondary breakup of the liquid shell. The spread factor of the hollow droplet remains unchanged as the impact velocity increases but is closely related to the surface wettability. The spread factor of the hydrophilic surface is larger than that of the hydrophobic surface. The effects of the surface wettability on the spread factor gradually reduce with the increase of the impact velocity. The effects of the impact velocity on the dimensionless jet length and the average wall heat flux are significant, while the surface wettability plays a negligible role in them. Improving the impact velocity increases the dimensionless length of the central jetting and the average wall heat flux, but this influence diminishes under a high impact velocity condition. Neither the dimensionless time spans of reaching the maximum spread factor nor the maximum average wall heat flux for the hollow droplet is influenced by the impact velocity and surface wettability and the development of the spread falls behind the heat transfer. Furthermore, the maximum spread factor increases with Reynolds number, and when Reynolds number is higher than 500, the increase in the maximum spread factor is no longer significant.
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Keywords:
- hollow droplet /
- droplet impact /
- central jetting
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[1] Moreira A L N, Moita A S, Panao M R 2010 Prog. Energ. Combust. 36 554
[2] Li D S, Qiu X Q, Yu L, Xu J, Duan X L, Zheng Z W 2014 Ind. Heating 43 1 （in Chinese)[李大树, 仇性启, 于磊, 许京, 段小龙, 郑志伟2014工业加热43 1]
[3] Liang G T, Guo Y L, Shen S Q 2013 Acta Phys. Sin. 62 024705 （in Chinese)[梁刚涛, 郭亚丽, 沈胜强2013物理学报62 024705]
[4] Rioboo R, Tropea C, Marengo M 2001 Atomization Spray 11 155
[5] Bi F F, Guo Y L, Shen S Q, Chen J X, Li Y Q 2012 Acta Phys. Sin. 61 184702 （in Chinese)[毕菲菲, 郭亚丽, 沈胜强, 陈觉先, 李熠桥2012物理学报61 184702]
[6] Li D S, Qiu X Q, Cui Y J, Zheng Z W, Ma P Y, Qi F L 2014 T. Chin. Soc. Agric. Mach. 45 25 （in Chinese)[李大树, 仇性启, 崔运静, 郑志伟, 马培勇, 祁风雷2014农业机械学报45 25]
[7] Kwon T J 2003 Ph. D. Dissertation（West Lafayette:Purdue University)
[8] Yokoi K 2011 Soft Matter 7 5120
[9] Solonenko O P, Gulyaev I P, Smirnov A V 2008 Tech. Phys. Lett. 34 1050
[10] Shukla R K, Kumar A 2015 J. Therm. Spray Techn. 24 1368
[11] Gulyaev I P, Solonenko O P, Gulyaev P Y, Smirnov A V 2009 Tech. Phys. Lett. 35 885
[12] Gulyaev I P, Solonenko O P 2013 Exp. Fluids 54 1
[13] Solonenko O P, Smirnov A V, Gulyaev I P 2008 The 5th International Workshop on Complex Systems Sendai, Japan, September 26——28, 2008982 561
[14] Shinoda K, Murakami H 2010 J. Therm. Spray Techn. 19 602
[15] Kumar A, Gu S 2012 Int. J. Heat Fluid Fl. 37 189
[16] Kumar A, Gu S, Tabbara H, Kamnis S 2013 Surf. Coat. Techn. 220 164
[17] Tabbara H, Gu S 2012 Int. J. Heat Mass Trans. 55 2081
[18] Brackbill J U, Kothe D B, Zemach C 1992 J. Comput. Phys. 100 335
[19] Yokoi K 2013 J. Comput. Phys. 232 252
[20] Guo Y, Wei L, Liang G, Shen S 2014 Int. Commun. Heat Mass 53 26
[21] Yang B H 2013 Ph. D. Dissertation（Chongqing:Chongqing University)（in Chinese)[杨宝海2013博士学位论文(重庆:重庆大学)]
[22] Ubbink O, Issa R I 1999 J. Comput. Phys. 153 26
[23] Liang C, Wang H, Zhu X, Chen R, Ding Y D, Liao Q 2013 CIESC J. 64 2745 （in Chinese)[梁超, 王宏, 朱恂, 陈蓉, 丁玉栋, 廖强2013化工学报64 2745]
[24] Liu D W, Ning Z, L M, Yan K, Sun C H 2016 Chin. J. Comput. Mech. 33 3027 （in Chinese)[刘冬薇, 宁智, 吕明, 阎凯, 孙春华2016计算力学学报33 3027]
[25] Song Y C, Ning Z, Sun C H, L M, Yan K, Fu J 2013 J. Combust. Sci. Technol. 19 549 （in Chinese)[宋云超, 宁智, 孙春华, 吕明, 阎凯, 付娟2013燃烧科学与技术19 549]
[26] Šikalo Š, Marengo M, Tropea C, Ganic E N 2002 Exp. Therm. Fluid Sci. 25 503
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