Computational Fluid Dynamics Modeling Of Discharge Tube In Fast-axial-flow CO₂ Laser

Fast-axial-flow CO₂ laser has been widely applied in laser processing industry with excellent beam quality and high output power. The optimization of gas flow field and discharge characteristics helps to improve the efficiency and output power of fast-axial-flow CO₂ lasers. In this paper, modern CFD (computational fluid dynamics) method is used to simulate the flow field of gas discharge in fast-axial-flow CO₂ lasers. Base on the numerical simulation and experimental verification of the existing structure and new designed structure, a new discharge tube with better flow field is obtained. The research results not only have important guidance significance for improving the performance of existing fast-axial-flow CO₂ lasers, but also help to reach much higher laser power. The main researchs in this thesis are as follows:(1)A 3-dimensional theoretical model for fluid dynamic processes in fast-axial-flow CO₂ laser is established. The theroretical governing equations are composed of three-dimensional mass, momentum, energy conservation equations and three temperature model equations. The geometric models are created by grid pretreatment software GAMBIT.(2) Combined with existing experimental results, factors which possibly impact the stability of glow discharge are analysed. According to the laser working parameters, the material physical properties, boundary conditions and solver control parameters are set reasonably.(3) Based on the computational fluid dynamics software FLUENT, a series of three-dimensional numerical simulations of the gas flow field in fast-axial-flow CO₂ laser are developed, datas of the flow field in discharge tube are got. The computational results agree with experimental results well, which verify the feasibility and effectivity of the developed theoretical modeling method. (4) The computational and experimental results are compared and analysed. The results show that the key factors that influence the stability of glow discharge are temperature, velocity and turbulence intensity The analysis results also explain why the performance of existing discharge tube in Lance3000 laser is worse than that of CP4000 laser,(5) Two kind of new discharge tube structures for fast-axial-flow CO₂ lasers are designed to improve the stability and uniformity of glow discharge. Both computational and exprimetal results show that the better discharge performance is obtained in one of the new discharge tube structures, which greatly simplifies the difficultly of the manufacture. The tube has advantages of simple structure, easy production, low cost and high practical value, and has been applied in the existing 4000W fast-axial-flow CO₂ lasers All these indicate that the theoretical simulation method has a guidance significance in practice.