Theoretical Modeling And Numerical Simulation Of Uniform Droplet Spray Process

As a new developed rapid prototyping technology, droplet deposition increasing material manufacturing technique is based on a layered manufacturing paradigm: the droplets are deposited exactly onto a movable substrate by alternative charging and deflecting uniform droplets from exciting a liquid jet by a periodic disturbance to fabricate certain structures. The technique succeeds in material melting temperature comparing to conventional rapid prototyping technology. Obviously, the technique has the advantages in a wide range of material, high efficiency, low energy consumption, and low cost, therefore is a potential attractive manufacturing method in the future. The key and difficulty of the technique is to obtain stable uniform droplet stream. However, there are a lot of factors that have influences on the uniformty of droplet stream, therefore only when the condition that all spray parameters match each other is satisfied, and then uniform droplet stream can be obtained. In this thesis, the mathematic model of the flow field and temperature field for uniform droplet spray process was established. The influence of spray parameters on droplet spray process had been studied via theoretical analysisand numerical simulation. The simulation results had been proved by experiments. All the research establishes a theoretical base for the application of droplet deposition increasing material manufacturing technique.The theoretical model of uniform droplet spray process had been established in this thesis. The calculation method for theoretical value of jet velocity and optimal frequency had been developed. Therefore the theoretical value and regularity of jet velocity and optimal frequency under different spray pressure were obtained, so the theoretical prediction for spray result had been realized. This not only offers comparison parameter for simulation results, but also will guide the proper determination of process parameters.The periodic sinusoidal vibration and amplitude modulated vibration of vibrating rod and plate had been realized via dynamic mesh code. The vibration displacement accorded well with the theoretical values at different time, so it was suitable to define the periodic vibration of vibrating rod and plate via dynamic mesh.With the aid of finite volume method, the flow field of wax droplet spray process has been simulated successfully via computational fluid dynamics software FLUENT. The influences of certain key factors, such as spray pressure, disturbance frequency, disturbance amplitude, the size and position of vibrating plate, crucible structure, and etc., on the configuration of jet and droplet stream were investigated systematically by simulation, disclosing the fact that the uniformity of droplet stream depends mostly on disturbance frequency, but disturbance amplitude also has certain influence on it. The influences of frequency ratio, degree of modulation, and carrier frequency on the configuration of droplet stream in the condition of amplitude modulation were also investigated, and the results had been compared with the results in normal condition, disclosing the intrinsic law of the process. The simulation results accorded well with the theoretical values.The simulation results in this thesis can provide reference data for charging, deflection, deposition, and solidification of droplets, laying a theoretical foundation for the realization of droplet deposition increasing material manufacturing technique and the proper determination of process parameters.