To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study th...To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD(Discrete Element Method and Discrete Element Method)coupled model.The influence of the powder flow concentration,powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered.The role played by the nozzle outlet width,the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered.The results show that,with increasing of nozzle outlet width,the powder flow concentration per unit volume at the nozzle focal point undergoes a non-monotonic behaviour(it first increases and then decreases).When the nozzle outlet widthδis 1.00 mm,the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal.By increasing the angle between the inner and outer walls,the powder flow concentration related to the upper focus decreases,the focus diameter increases and the powder flow aggregation worsens.The powder flow concentration increases first and then decreases with increasing incident angle.When the incident angleθis 30°,the powder flow exhibits the best agglomeration properties.When the outlet width is smaller,the angle between the inner and outer walls is larger,and when the incident angle is set at 30°,the powder flow concentration of the coaxial nozzle can be effectively improved.展开更多
在增压条件下对一种旋流式气液同轴喷油器的雾化特性进行研究。在不同的环境背压条件下,采用PDPA测量距离喷口处70mm的液雾分布,研究了环境背压、气液相对速度、以及燃油流速对索特平均直径(Sauter mean diameter,SMD)的影响规律。结果...在增压条件下对一种旋流式气液同轴喷油器的雾化特性进行研究。在不同的环境背压条件下,采用PDPA测量距离喷口处70mm的液雾分布,研究了环境背压、气液相对速度、以及燃油流速对索特平均直径(Sauter mean diameter,SMD)的影响规律。结果表明:当保证燃油流速一定、气液相对速度一定的条件下,SMD随环境背压的增大而减小;当环境背压及燃油流速一定的条件下,SMD随气液相对速度的增大而减小;当保证雾化空气压力以及环境背压一定的条件下,燃油流速对SMD的影响规律存在一个拐点,随着燃油流速的增加,SMD先增加后减小,在文中的试验条件下,燃油流速拐点值约为9.91m/s。根据试验数据整理出SMD与环境背压、气液相对速度及燃油流速的拟合公式。展开更多
基金the National Natural Science Foundation of China(Project No.51675226)Natural Science Foundation of Liaoning Province(Project No.20180550167)Key Projects of Liaoning Province(Project Nos.LJ2017ZL001,LJ2019ZL005).
文摘To improve the agglomeration of powder in a coaxial powder feeding nozzle used in the frame of a laser energy deposition technique,the influence of several parameters must be carefully assessed.In the present study the problem is addressed by means of numerical simulations based on a DEM-CFD(Discrete Element Method and Discrete Element Method)coupled model.The influence of the powder flow concentration,powder flow focal length and the amount of powder at the nozzle outlet on the rate of convergence of the powder flow is considered.The role played by the nozzle outlet width,the angle between the inner and outer walls and the powder incident angle in determining the powder flow concentration is also considered.The results show that,with increasing of nozzle outlet width,the powder flow concentration per unit volume at the nozzle focal point undergoes a non-monotonic behaviour(it first increases and then decreases).When the nozzle outlet widthδis 1.00 mm,the powder flow concentration at the focal point is maximal and the powder flow convergence can be considered optimal.By increasing the angle between the inner and outer walls,the powder flow concentration related to the upper focus decreases,the focus diameter increases and the powder flow aggregation worsens.The powder flow concentration increases first and then decreases with increasing incident angle.When the incident angleθis 30°,the powder flow exhibits the best agglomeration properties.When the outlet width is smaller,the angle between the inner and outer walls is larger,and when the incident angle is set at 30°,the powder flow concentration of the coaxial nozzle can be effectively improved.
文摘在增压条件下对一种旋流式气液同轴喷油器的雾化特性进行研究。在不同的环境背压条件下,采用PDPA测量距离喷口处70mm的液雾分布,研究了环境背压、气液相对速度、以及燃油流速对索特平均直径(Sauter mean diameter,SMD)的影响规律。结果表明:当保证燃油流速一定、气液相对速度一定的条件下,SMD随环境背压的增大而减小;当环境背压及燃油流速一定的条件下,SMD随气液相对速度的增大而减小;当保证雾化空气压力以及环境背压一定的条件下,燃油流速对SMD的影响规律存在一个拐点,随着燃油流速的增加,SMD先增加后减小,在文中的试验条件下,燃油流速拐点值约为9.91m/s。根据试验数据整理出SMD与环境背压、气液相对速度及燃油流速的拟合公式。
