【作者】 陈功；

【导师】 王福新；

【作者基本信息】 上海交通大学 ， 力学， 2020， 博士

【摘要】 为解决飞机结冰现象所带来的一系列问题,防除冰技术一直以来都是航空制造企业、科研院所、运营公司所关注的焦点,并取得了积极进展。防除冰技术的目的旨在破除冰在飞机表面的附着力,使其更难于附着在机体表面或更容易发生脱落。因此,研究和掌控结冰附着特性及其变化规律,必将有助于飞机防除冰的技术进步和实施推广。根据表征形式不同,结冰附着力可分为粘附力与粘聚力。然而在研究分析现状时发现,在实际工程问题中常常会混淆粘附力和粘聚力的概念,而且绝大部分研究主要关注于粘附力及粘聚力最终表现出的静态特性,尤其是对壁面结冰过程中的非稳态演化及其机制缺乏研究,这将导致在预测飞机冰脱落、采取防除冰技术等问题时会发生较大的偏差。为了解决上述问题,需要更深入地研究冰的力学性能与结冰进程中物理性质变化的内在联系,分析粘附力与粘聚力的相关性,并总结归纳出它们在壁面结冰过程中演化的理论模型。该研究成果将有助于防除冰技术的发展升级,促进相关学科的融合与发展。本文以探索和确定壁面结冰过程中粘附力与粘聚力演化的规律和机制为主要目的,以壁面结冰过程中不同阶段的物理性质及传热特性为线索,进行以下几个方面的研究:1、以工程试验中的冰脱落现象及数据信息为依据,并根据冰脱落的表征提出粘附力与粘聚力在空间上的相关性和在时间上的演化性这一假设。2、从粘附力与粘聚力本身的定义和原理出发,通过结冰物理测力试验,验证其粘附力与粘聚力在空间上的相关性与时间上的演化性,以期获得其相应的变化规律。3、在微观层面上,分析研究壁面结冰及冰生长过程中的几何特征、分枝结构、生长速度的演化。同时,将壁面结冰与自由结冰中的对应参数进行比较,分析两者之间的区别与关联性,探究和推测“壁面效应”的本质。4.研究壁面结冰各阶段壁面与冰层(枝)、冰层(枝)与过冷水之间的传热特性,着重关注冰层内部温度场在结冰进程各阶段的变化规律,由此推导出不同初始条件下温度随时间及空间变化的函数。5、以当前结冰粘附力与粘聚力的相关理论为主要依据,结合本文上述研究结果,建立以时间与空间为自变量、温度为传递函数、粘附力与粘聚力为目标函·数的壁面结冰非稳态附着力预测模型,以期作为制定防除冰技术方案时的参考。对应上述各项研究内容,本文具体研究过程及结果为:1、通过涡扇发动机冰脱落研究试验发现,冰脱落的时间及脱落后的残余冰量与环境温度及叶片转速密切相关,冰脱落在形式上呈现“冰分离”和“冰断裂”两种形式,且冰脱落特性随时间的发展有所变化。试验结果表明,外部载荷越大,冰脱落越容易发生,脱落的程度也越大。结合受力分析,提出了“粘附力与粘聚力在壁面结冰过程中是变化的”这一假设。2、根据壁面结冰过程中的物理特征变化,具体划分了壁面结冰的结冰触发、等温相变、等熵冷却、平衡稳定等各个阶段;然后在上述不同结冰阶段进行粘附力与粘聚力的测力试验。一系列试验结果表明,壁面结冰初期的粘附力与粘聚力较小,随着结冰进程的推进,它们在数值上逐渐增大,并最终达到稳定。该试验结果证实了“壁面结冰时粘附力与粘聚力存在演化性”这一假设的合理性,并初步建立了它们与结冰过程的耦合关系。3、通过显微镜观测不同初始温度条件下,壁面结冰后冰枝生长的过程。观测结果表明:冰枝自壁面生长后,其总体形态、分枝结构及生长速度在其生长过程中是变化的。靠近壁面的冰枝尺度与分枝角在数值上均偏大,且生长速度较慢;当冰枝生长远离壁面后,其宽度与分枝角均减小,且在数值上分布更均匀,与对应条件下自由结冰冰枝生长的特性相近。上述结果推测,冰枝生长过程中,其前端的局部温度是持续变化的。4、根据3中观测到的冰枝生长表征,引入非稳态传热理论,对壁面结冰各阶段的冰层与壁面间的传热及温度场的变化进行解析。分析结果表明,当初始过冷度较低时,冰层在竖直方向上平滑生长,冰层内部温度变化单一且缓慢;而当过冷度较高时,冰层在竖直方向上复合生长并产生“海绵冰”,在海绵冰的生长及二次填充过程中,冰层内部的温度场应根据冰层结构分段计算。5、分别引用现有文献中关于粘附力/粘聚力与温度的对应关系,结合4中壁面结冰过程中的传热函数,建立了以初始过冷度、结冰时间及冰层内部空间位置为自变量、粘附力与粘聚力为目标函数的预测模型。通过该模型可知,非稳态粘附力与粘聚力均随结冰进程的推进而增大并最终收敛。距离壁面位置越近,该横截面上的粘聚力的形成和递增就越早,反之则会有所延迟。本文的创新点为:在基础理论上,探索并发现了壁面冰生长过程中的总体与分枝形态分层演化规律,揭示了局部过冷度控制壁面冰结构和附着力演化的机制,并结合壁面传热分析和试验数据,建立了非稳态附着力的分阶段演化预测模型,可预测实际壁面结冰附着力的变化过程。在研究方法上,建立了壁面结冰定温触发及分层测量附着力的试验测试方·法,相对而言,可以在确定的温度下准确测量不同时间和高度的冰附着力,为深入研究冰附着力的时间演化规律提供了有效的解决方法。更多还原

【Abstract】 To solve the issue caused by unexpected icing on aircraft,deicing and anti-icing technology is always emphasized by aviation manufacturer,research institutes and operation company.Deicing and anti-icing technology aims at destroy the adjoin force of the ice on aircraft surface so as to make more difficult attaching or easier shedding.In this case,it is helpful to clarify the characteristics and regularity of ice-adjoin for the development and popularization of deicing and anti-icing technology.Ice-adjoin could be further classified as ice-adhesion and ice-cohesion according to their different representation.However,current research status shows that the concept of ice-adhesion and ice-cohesion is always confused during some engineering occasion.In addition,more attention has been paid on the final static characteristics of ice-adhesion and ice-cohesion rather than on their evolutionary regularity during substrate icing.This will leads uncertainties for the prediction of ice-shedding from aircraft.To solve the problem above,correlation is required between ice-adhesion and ice-cohesion.It is also important to investigate in-depth to find the relationships between ice-mechanism and physical change during substrate icing.Therefore,an analytical model could be established.The result of this research helps improving the technology and encourage the development of relevant subject.The main purpose of this paper is to identify the evolutionary regularity and discipline of ice-adhesion and ice-cohesion according to the physical pattern and heat conduction.The research focus on following aspects:1.Statement is raised that both temporal and spatial evolution of ice-adhesion and ice-cohesion from the ice-shedding phenomenon from engineering experiment.2.Stress-testing experiment is conducted to validate the occurrence of both temporal and spatial evolution.Afterward,a qualitative trend is summarized by the combination of basic definition and principle of substrate icing.3.Geometric characteristics,branching structure and growing velocity of ice crystal during substrate-icing is observed in microscope view.Meanwhile,corresponding parameters from substrate-icing and free-icing is compared to find both·difference and relationship of them to identify the essence of “wall-effect”.4.The characteristics of heat conductivity from substrate to ice(crystal)layer as well as from ice(crystal)layer to supercooled water is analyzed purposefully.The function of temperature changes with the temporal and spatial variable is induced by analyzing the temperature evolutionary regularity during substrate icing process.5.Associated with the current theory of ice-adhesion and cohesion,temperature evolution is used as parameterized equation to establish the model for ice-adhesion and cohesion prediction,as the reference for de-icing scheme design.To fulfill the research task above,the content of this thesis will be displayed in following sequence:1.It is shown in turbo-fan blade ice shedding experiment that both time for shedding and volume of residual ice are closely dependent to either temperature or rotational speed.Experiment results illustrate generally that more series ice-shedding easily occurs when larger external load is applied.It is also found that ice-shedding could be contribute to either “ice-separation” or “ice-breaking” according to shedding mode.In addition,variation of shedding performance is found during the process of ice accumulation on the blade.Therefore,an assumption “evolution of both ice adhesion and cohesion occur during substrate icing process” is raised by force analysis.2.According to change of physical properties,substrate-icing is generally divided into four phases: ice-triggering,iso-thermal freezing,isentropic cooling and balancing.Afterward,measurements of both ice-adhesion and ice-cohesion are conducted in each phase.The result shows that both adhesion and cohesion increase over time during the substrate-icing process and then converge at last.Thus,the assumption that “evolution of both ice adhesion and cohesion occur during substrate icing process” is validated and the relationship between such evolution and ice-progression.3.The process of ice crystal(layer)growing in different initial supercooling is observed by optical microscope.The results show that general morphology,branching structure and growing velocity vary over time during the vertical growth.In the area near the substrate,both the branching angle and branch width are numerically larger;while in the area far from the substrate,branching angle and branch width become smaller and more regular,of which the features are more similar to that of free-icing.All the results indicate that local temperature around the crystal tip varies during its growing process.·4.Based on the illustration of ice crystal(layer)growing,unsteady-state heat transfer theory is applied to analyze temperature variation of substrate and ice-layer during substrate icing process.The analysis shows that the temperature evolution of ice layer proceeds generally during smooth growth in low supercooling condition.While in high supercooling condition,the complex growing of ice layer proceed with the generation of “spongy ice” at first and following with the “second filling” of residual liquid component.In this situation,temperature evolution becomes more complicated than that in low supercooling.5.Referring to the relationship between temperature and ice adhesion/cohesion from current literature.the predictive model is constructed by the heat transfer function obtained in Chapter 4,of which the variable is initial temperature,freezing time and internal position of ice layer.According to this model,both ice adhesion and cohesion increases with the progression of substrate icing and then converges at last.In the area near the substrate,ice cohesion occurs and progresses earlier while they are delayed where far from substrate.The significance and innovation of this thesis are:For theory,the evolution general configuration and branching features of ice crystal during substrate icing progression.The law of local-supercooling-dependent ice crystal structure and ice adhesion/cohesion evolution are revealed.The piecewise-model of ice adhesion/cohesion evolution is established is established with the analysis of heat transfer during substrate-icing experiment data for adhesion/cohesion prediction.For research method,a method of ice adhesion/cohesion stratified measurement by regular temperature trigger is created in order to test ice adhesion/cohesion at different position within various supercooling condition.Such method is practical for the further research of ice adhesion/cohesion evolution.更多还原