Investigations Of Deformation And Breakup Process Of Single And The Distribution Characteristics Of The Sub-droplet In Airflow

In order to study the mechanism of single droplet breakup in a continuous and uniform air jet flow and provide theoretical analysis foundation for correlated phenomena in the process of the droplet deformation and breakup,the internal flow mechanism is studied by the experimental approach.An experiment system has been designed to research the droplet deformation and breakup under different flow field structure.A droplet generator producing different droplet diameter has been designed to study impact of initial diameter on breakup morphology of single droplet in cross airflow,and relationship between droplet deformation rate and droplet breakup mode has been studied.The effects of the different thickness distribution of the thin disc droplets in the direction of airflow on droplet breakup morphology are analyzed.In order to obtain characteristics of single droplet deformation and breakage and movement characteristic in deformation phase in a continuous and uniform hot air jet flow,an experiment system has been designed which can generate continuous and uniform hot air jet flow with different distributions of velocity and temperature rapidly,and the experimental results can be used to build the mathematical model of the number and sauter mean diameter of sub-droplet in the single droplet breakup region.In order to obtain the data of deformation length,distance in horizontal direction of droplet and the number of sub-droplet,sub-droplet diameter at different location in the single droplet breakup region from image by the High-speed camera,a spray field digital image processing program has been designed and developed based on the technology of digital image processing.The High-speed camera is applied to measure single droplet deformation and breakage and sub-droplet in the core/bag breakup regime,plume/sheet-thinning breakup regime and sheet-thinning breakup regime.Impact of the initial diameter and the airflow temperature on breakup morphology of single droplet in cross airflow has been studied.The relationship between the character time of droplet breakup and the airflow temperature,initial droplet diameter and aerodynamic force have been obtained.The changing rules of the percentage of sub-droplet mass,the level of droplet breakup with the airflow temperature,initial droplet diameter and aerodynamic force have been established.The standard deviation rate model is put forward to study the uniformity of diameter and percentage mass of sub-droplet in the single droplet breakup region.The changing rules of droplet level velocity? acceleration?deformation drag coefficient with deformation time and the We number have been analyzed.In order to further understand characteristics of single droplet deformation and breakage in the airflow,as well as contribute to select condition variables in the process of mathematical modeling,the fuzzy mathematical theory is used to study impact of initial diameter,airflow temperature?airflow velocity on droplet broken total time,the percentage of sub-droplet mass,the level of droplet breakup changed with aerodynamic force.In order to obtain the mathematical model of the number and sauter mean diameter of sub-droplet in the single droplet breakup region,two data mining methods that are the multiple linear regression model and the nonlinear BP neural network model respectively have been used to build mathematical models,as well as the single droplet breakup region has been divided into a and four blocks.In the models,the air flow state and initial diameter and time variable have been used as conditional variables,and the number and SMD of sub-droplet have been used as target variables.In the three kinds of breakup mode,the calculated results by the multiple linear regression model and the nonlinear BP neural network model training samples forecast samples both are in agreement with the measured ones.When the mathematical models are established,the number and SMD of sub-droplet in the single droplet breakup region can be obtained by conditional variables.The methods can be provided the reference for the droplet distribution model and the optimization process of droplet breakup in numerical simulation for combustion process in aero-engine combustor.As well as impact of conditional variables on target variables and the inner link among variables can be obtained by the multiple linear regression models.The variables affecting ability through the multiple linear regression models and the fuzzy mathematical theory are similar,suggesting reasonable mathematical models used in the paper.