Study On Heat Transfer Characteristics And Effects Of Electrothermal Aircraft Deicing

Ice accretion is one of primary hazards to flight safety. Aircraft anti/de-icer is important equipment which can improve airplane safety performance and can reduce flight icing accident. Due to high efficiency, low energy consumption and easy to control, electrothermal deicing is becoming one of the most widely applied techniques of aircraft deicing. The development of ice protection theory and deicing technique is important for flight safety. It is vital to carry out the study of aircraft electrothermal deicing mechanism and law, especially because domestic study of aircraft electrothermal deicing just begins and level of study lags far behind developed countries.By means of theoretical analysis, numerical simulation and experiment, phase-change heat transfer characteristic, ice shell phenomenon and its effect, coupled thermo-mechanical characteristic and ice ridge formation characteristic are studied in this thesis. The study focuses on revealing electrothermal deicing mechanism and understanding the influence on deicing efficiency. The research results will not only provide the theoretical basis for the improvement of present electrothermal deicing system, but also provide the technical support for the development of new deicing technique.This thesis is divided into six chapters as follows:The first chapter is the introduction. The significance and status of the investigation for aircraft electrothermal deicing, the problems and gaps between home and abroad investigation are reviewed. The present research work of this thesis is also described briefly in this chapter.In the second chapter, the study of heat transfer characteristics during aircraft electrothermal deicing process is presented. The traditional phase-change model is applied to the simulation of aircraft electrothermal deicing by using finite volume method based on enthalpy model. The ice phase-change heat transfer characteristics during electrothermal deicing process are studied systemically. The research emphasis is on the effects of heating manner, cooling time, heater power density and heater gap width on phase-change heat transfer characteristics, as well as the effects of ice shedding on heat transfer characteristics. Finally, some important heat transfer characteristics during electrothermal deicing process are confirmed in icing wind tunnel. The study shows that periodic heating manner under high power is superior to continuous heating under low power when reasonable cooling time and heating power density are adopted. Chapter 3 presents ice shell phenomenon and its effects on electrothermal deicing on the leading edge of aerofoil. Combined with the effect of external forces, melting model is established by theoretical analysis. Effects on ice shell melting characteristics of aerodynamic pressure and gravity are investigated. Furthermore, Ice shell phenomenon is confirmed in icing wind tunnel. Ice sliding is analyzed theoretically. Ice shell and its effects are obtained in this chapter. The research result shows that aerodynamics pressure increases the melting speed of ice shell and delays the ice shell shedding simultaneously. Ice shell results in severe aerodynamics performance.The study of coupled thermo-mechanical characteristics is presented in chapter 4. The effect of aerodynamics on stress distribution characteristics in the ice layer is studied by finite element method based on unstructured mesh. Furthermore, the effect on stress distribution characteristics of electrical heating is studied. The study shows that stresses in the ice layer caused directly from aerodynamic loading are not significant when the flight velocity is low. While coupled thermo-mechanical characteristic leads to remarkable increasing of stresses in the ice under the condition of electrothermal deicing. Consequently, it results in crack in the ice and speeds up ice shedding. Finally, the effects on deicing of coupled thermo-mechanical characteristics are validated in icing wind tunnel.Chapter 5 is the investigation of ice ridge formation mechanism during electrothermal deicing process. The ice ridge formation is tested in icing wind tunnel. The effects on ice ridge formation of icing temperature, inflow velocity and heater power density are investigated. Combined with ice ridge formation obtained by experiment, the mechanism and growth of ice ridge formation are further analyzed. The study shows that ice ridge is formed far apart from the ice protection region and grows forward gradually.The concluding remarks are given in chapter 6. The summary of current work is presented and expectation for future work is pointed out as well.