Study On Evolution Mechanism Of Ice Adhesion During Aircraft Icing Problem

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.