A three-dimensional, transient, turbulent, local thermodynamic equilibrium (LTE) model of plasma arc was proposed in order to study the arc dynamics and plasma characteristics in a plasma torch. Computational fluid dynamics software ANSYS CFX was adopted in this study. The research work mainly involved the anode arc root reattachment process, the arc and flow interaction inside the argon-hydrogen plasma torch and plasma temperature and velocity distributions predictions. The results show that as the arc is dragged downstream by the cold incoming gas, the arc length increases and the arc voltage and the local electric field strength increase. When the local electric field strength is high enough, the arc breakdowns and a new arc root is formed. The arc voltage fluctuation lead to the fluctuations of maximum plasma temperature and velocity at the torch exit and the lagged time is about 10μs. The plasma flow and heat transfer inside the plasma torch have strong three-dimensional effects. Compared with the temperature distribution, the plasma velocity distribution has stronger three-dimensional effect and is more concentrated into the center.%基于局域热力学平衡假设,建立三维非稳态等离子电弧的湍流模型,应用计算流体力学软件ANSYS CFX模拟了氩/氢等离子喷枪内阳极弧根的再附着过程、电弧与气流的相互作用以及等离子体温度和速度分布.结果表明,在冷气流推动下,阳极弧根向喷嘴下游移动,电弧被拉长,弧电压升高,电场强度增大.当电弧向下游移动到电场强度足够大时,电弧击穿并形成新的弧根.喷枪内电弧波动导致喷枪出口等离子体最大温度和最大速度发生波动,滞后时间为10μs.喷枪内的流动与传热具有明显的三维特征,与温度分布相比,速度分布的三维特征更明显且更向中心处集中.
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