【作者】 陈彦；

【导师】 吴晓敏；

【作者基本信息】 清华大学 ， 动力工程及工程热物理， 2012， 硕士

【摘要】 结霜现象广泛存在于制冷空调、航空航天和风力发电等多领域，并带来很大的危害，前人围绕结霜现象进行了很多研究，近年来这些研究不断深入到霜层内部细节和动态结构特征，但对于结霜过程中霜层和湿空气参数空间分布变化研究得较少，对风力机叶片表面覆冰的研究也比较少。本文实验研究了环境参数和冷面温度对结霜初期过冷水珠和结霜过程中冰晶体积分数的影响，数值模拟研究了霜层生长过程中霜层和湿空气参数的变化规律以及风力机叶片覆冰过程中攻角和风速对覆冰量及覆冰形貌的影响。本文通过对结霜过程的可视化研究发现，在霜晶出现之前，冷面上都经历了水珠生成、聚合长大和水珠冻结的过程，但水珠的出现时刻及冻结时间受环境因素的影响：风速越大、冷面温度越低以及环境温度越低，则冷面上过冷水珠越早出现，同时水珠的冻结时间越短。在一定范围内，冷面温度越高、风速越大、环境温度越高，则冰晶体积分数越高。改进了课题组原有结霜模型的质量传输判据和模型，利用Fluent模拟了霜层生长过程，考察了冷面附近霜层和湿空气参数随空间和时间的变化规律，以及环境温度、相对湿度、风速和冷表面温度对冷面附近霜层和湿空气参数的影响，结果表明冰晶体积分数受环境工况影响的规律跟实验结论较为符合，并且风速越大，冰相体积分数沿空气流向分布越均匀。在霜层内部，时间越久、高度越低，则冰相体积分数越高，并且沿着空气流向逐渐降低，且入口附近降幅较大，但出口附近有小幅度的上升。在冷面结霜模型的基础上，采用湍流模型和新的质量传递模型对夹杂过冷水滴的空气流经叶片表面时的覆冰进行了初步的模拟。结果表明过冷水滴受空气流场影响较小，覆冰一般在迎风面发生；当叶片攻角增加时，过冷水滴随着来流撞击到叶片下表面的几率增加，覆冰面积和覆冰质量均增加；由于驻点处受来流的垂直撞击，故驻点处覆冰量较少，两侧覆冰量较多；随着来流风速的增加，叶片表面覆冰量增多，其原因是：单位时间内撞击到叶片表面的过冷水滴数增加，同时单位体积内撞击到叶片表面的过冷水滴百分数增加，使得叶片表面覆冰量明显增加。更多还原

【Abstract】 Frosting does much harm in industries of cooling systems, aerospace, and windpower generation. Much research has been conducted on frosting. In the recent years,the research has been deepened into the internal details of frost layer and dynamicstructure characteristic. However, there is not enough research on the frost layer andwet air parameters during frosting process. The research on ice formation on thesurface of wind turbine blade is also insufficient. This paper studied the influence ofthe environment parameters and cold surface temperature on the super-cooled waterbead and ice volume fraction through experiment. Then studied the rule of frost layerand wet air parameters in process of frost growing, and the influence of attack angleand velocity for icing on wind turbine.Through vision research on initial frost formation, this paper finds that theformation of super-cooled water droplet and freezing is influenced by environmentalcondition. Before the frost crystal appearing, there are drops generation,polymerization, and freezing on the cold surface, but the appearing moment andfreezing time is influenced by environment. When the velocity is faster, thetemperature of cold surface and environment is lower, the super-cooled water dropletwill appear earlier and the freezing time is shorter. The volume fraction of ice crystalwill decrease with the cold surface temperature decreasing, the velocity increasing andthe ambient temperature increasing. This paper improved the quality transmissioncriterion and model for the traditional frost model, simulated the growth process offrost layer, examined the changing rule for the frost layer and wet air parameters withspace, time, environmental temperature, relative humidity, wind speed and cold surfacetemperature, found that the simulated results is conform to experimental results, andthe greater the velocity, the more uniform the ice phase volume fraction along the airflow distribution. The ice volume fraction inside frost layer is bigger when time islonger and height is small, and reduces gradually along the air flow, with highlydecreasing near the inlet and a small rise near the export.On the basis of the frost model under cool surface, an ice accretion model on windturbine surface is established with turbulence model and the new mass transfer model, and the icing procedure on the wind turbine is simulated when the air which containssuper-cooled water droplet flows through the blade. Then find that: Firstly, the freezingoccurred in the windward side generally, because there is little impact of air flow onthe super-cooled water droplet; Secondly, the blade surface icing morphology changeswith the attack angle. With the attack angle increasing, the icing area and icing are alsoincreasing; Thirdly, the air flow strikes to the stagnation point vertically, so the areanearby of the stagnation point has more ice; Finally, when the velocity increases, thesuper-cooled water droplet number which strikes the blade also increases in unit time,and then makes the ice quantity on the blade surface increased significantly.更多还原