Investigation On Growth Mechanism And Model Of Substrate Icing

When a plane passes through a cloud,supercooled water will accumulate on the surface,destroy the aerodynamic shape of the aircraft and affect the normal operation of the engine and sensors.Therefore,every year a number of accidents will happen,which is a major hidden danger of flight safety.In recent years,the researchers focus on the application of various new materials on aircraft and the rise of anti-icing surface materials make the influencing factors of surface materials.However,the current icing model of aircraft is mainly based on the rules of free icing,which can’t explain the law of substrate icing and the influence of the substrate on icing.So the rule of substrate icing needs to be studied.In this paper,based on the theory of free icing and substrate icing existed,the typical experimental design of substrate icing growth is established,to observe the process of ice branches growing near the substrate,to research the effect of supercooling degree,the free energy on the substrate and the direction of ice growth on the ice speed and shape,and then the mechanism of the substrate factoring on the ice branches growing is obtained through theoretical analyzing.It shows:1.Although the growth of substrate icing is similar to the free ice branch,the materials of the substrates,surface contact angle,supercooling degree of icing and trigger angle are greatly affect the growth of substrate icing.(1)The speed of ice growth is inversely proportional to the free energy of the substrate,and the velocity of the hydrophilic surface is lowest at about-2℃,but the free energy of the substrate doesn’t affect the speed above the temperature.Moreover,the speed of ice growth on the hydrophobic surface is close to that of free ice.The free energy of the wall doesn’t change the angle and radius of the tip of the ice branch,but only changes the growth speed.(2)The trigger angle is positively related to the growth of the wall ice branches,and the growth direction of the ice branches will lead to the growth of the ice branches.(3)With the increase of the supercooling degree and the thermal conductivity of the substrate,the influence of the free energy and the trigger angle on the substrate decreases rapidly.2.The growth mechanism of wall ice branches is understood:(1)The analysis of the heat transfer of ice growth shows that the free energy of the substrate effects the speed of ice growth because of the heat transfer from tips,but changing the properties of ice.(2)The direction of the ice growth isn’t changed by the surface of substrate,even if the morphology varies with different heat conduction(ice branch or ice layer),but determined by the direction of the initial ice core.3.The understanding of the substrate icing is improved: when ice forms branch,and the supercooling degree is less than 5K,the effect of the surface energy effects on growth speed and direction of the substrate icing is considered,so the speed of substrate icing is the average of velocity with high-angle and low-angle triggers.In this paper,the growth speed of substrate icing is inversely proportional to the surface energy,and the prediction model of supercooled water icing considering the surface free energy is established,which is instructive for aircraft icing prediction and anti-icing design.