Study On The Influence Of Mutual Interferences Of Supercooled Water Droplets On The Impacting And Freezing Process

The problem of Supercooled Large Droplets(SLD)impacting and freezing is a hot issue of aircraft icing research.Experimental research is one of the most important methods.In recent years,the ice-wind tunnel experiments mainly focused on the kinetic problems during the process of SLDs impacting and freezing.However,the distribution of Supercooled Large Droplets in the real cloud-fog environment has not been considered.In 2014,Appendix O of the FAR25 issued the requirements of the airworthiness certification for the environment of Supercooled Large Droplets(SLDs).However,the major icing wind tunnels around the world still have limited ability to simulate the complicated cloud environment in Appendix O.Therefore,the research on the mechanism of multiple SLDs impacting and freezing is extremely necessary.There are experimental results which show the differences of water content(LWC),average particle size(MVD)and degree of super-cooling of the droplets can greatly affect the impacting and freezing process.In the real cloud-fog environment,the distribution density of SLDs can be up to 10~6/m~3,and there are few experimental studies on the interference of SLDs'impacting and freezing process.Under such circumstances,the paper designs the experiment to study the physical process of multiple SLDs impacting and freezing successively,compare the experimental results with the impacting and freezing process without mutual interactions.High-speed cameras were used to shoot the impacting-freezing process of SLDs that offset a certain distance away from each other and successively impact on the substrate.The experimental studies the relationship between the offsets of two SLDs,the time intervals of successive impacts and the freezing morphology,the freezing speed.The experiment shows that the interferences between SLD can inhibit the process of impacting and shrinking,the smaller the offset position between SLDs is,the stronger the inhibition effects are.The time interval of the SLDs impingement has limited effects on the shrinking process.The interactions have significant effects on slowing down the freezing speed.The shorter the interval time is,the more slow the freezing speed is.The smaller the relative offset of the SLDs is,the more slow the freezing speed is.On the basis of the original single water droplet impacting model,the unsteady impact and heat transfer model of multi-droplets is obtained.The results of the paper further reveal the freezing characteristics of SLDs impact process and provide some references for the related icing wind tunnel experimental technology research.