Experimental Study On The Temperature Effect Of The Dynamic Characteristics Of The Supercooled Large Droplet

In recent years, the flight accident caused by supercooled large droplet(SLD) caused great concern and research boom of people. The average diameter of SLD is usually considered to be more than 100?m. The main difference of dynamics characteristics between SLD and small water droplets are dynamic behaviors including obvious deformation, breakup, and splashing. SLD icing could not make the most of anti-icing systems achieve complete deicing, and it will result in sharp decline in aircraft aerodynamic performance, especially for SLD icing of aircraft engine components, the flow characteristics of engine inlet will be greatly changed, ice shedding can easily damage engine blade, and even cause the engine to stall, and serious threat the flight safety.The researches of SLD dynamics at home and abroad were mainly carried out under the normal temperature condition, and the SLD dynamics models used in numerical simulations are also obtained from the experimental data of normal temperature. However, real aircraft icing environment temperature is usually between 0 and-20℃. This low temperature environment usually results in the changes of physical properties, internal pressure distribution of SLD and the changes of the physical properties of the surrounding medium(air), which will affect the droplet dynamics characteristics and the icing of aircraft. Hence, the changes of SLD dynamics characteristics at low temperature have important significance for the correction of the traditional SLD dynamics model.As a consequence, this paper focuses on the temperature effect based on contrast experiment research methods, By designing the rapid contraction section, using the piezoelectric droplet generator system and the high-speed camera technology, solved the difficult problems of the drop diameter measurement, velocity control and droplets image capture technology. The parameters measurement methods of water and air are studied, including image processing technology, the droplet diameter velocity, and temperature measuring method, air velocity calibration method, and the verification of the system’s feasibility and reliability are finally completed.The SLD dynamic characteristics contrast experiments were conducted at different ambient temperature. The experimental results showed that: with decrease of the ambient temperature, deformation rate of droplets, the critical deformation rate of droplets, resistance coefficient(reference local dynamic pressure and normal projected area of initial droplets) decreased, especially in the initial droplet deformation stage, temperature effect is more obvious. Regardless of the bag breakup or stamen breakup, breakup range at low temperature is smaller, and breakup time is longer; secondly stamen breakup can cause secondary breakup more easily, and stamen breakup is more sensitive to temperature changes.The main innovation of this research: discover new physical phenomena and laws of SLD at low temperature; based on the TAB breakup model, the critical deformation rate of droplets is modified, and the temperature effect model of the critical deformation rate is established. The child droplets uniform distribution model of bag breakup and stamen breakup are preliminarily established under the condition of the normal temperature and the low temperature. This two models further describe the real physical process of the water droplet breakup, and have a certain effect on the water collection coefficient and the droplet impact limit, and it makes the existing design method of the ice protection system face new challenges.