等离子射流在圆柱充液室中扩展、掺混的实验及数值模拟

Experiment and numerical simulation for propagating and mixing process of the plasma jet in liquid medium

关键词:  等离子射流  液体工质  Taylor空腔  Taylor-helmholtz不稳定效应

Key words:  Plasma jet  Liquid media  Taylor cavity  Taylor-helmholtz instability

摘要:

为了研究等离子射流与液体工质相互作用特性,设计了圆柱型充液室,运用数字高速录像系统观察了等离子射流的扩展过程,重点研究了放电电压对等离子射流扩展特性的影响。实验结果表明,等离子射流在液体中扩展时,两相流体存在较大的速度差,Taylor-helmholtz不稳定效应导致强烈的两相湍流掺混,Taylor空腔的亮度在时空上呈非单调分布；放电电压越大,Taylor-helmholtz不稳定效应越强。在实验基础上,建立了等离子射流扩展的二维轴对称非稳态可压缩流的数学模型,并进行了数值模拟,获得了射流场中Taylor空腔界面的形态变化,以及流场中压力、速度、温度、湍动能和湍流耗散率的分布特性。由Taylor空腔界面扩展云图计算得到的Taylor空腔轴向扩展位移与实测值吻合较好。

Abstract:

In order to explore the interaction properties of the plasma jet with liquid medium, the cylindrical observing chamber was designed. High speed digital camera system was used to record the process of plasma jet propagating in liquid. The influence of discharge voltage on the characteristics of plasma jet was analyzed. The results indicate that, when the plasma jet propagates in liquid, the velocities of the plasma jet and the liquid are much different, and the turbulent mixing induced by the Taylor-helmholtz instability is strong. The brightness of Taylor cavity is temporal and has a spatial nonmonotonic distribution. The larger the discharge voltage, the greater is the Taylor-helmholtz instability. Based on the experiment, a two-dimensional-axisymmetric unsteady compressible flow mathematical model was developed and the numerical simulation was also conducted. The interface change of the Taylor cavity, the distributions of pressure, velocity, temperature, turbulent kinetic energy and turbulent dissipation rate were obtained.The axial displacement of the Taylor cavity calculated through the pictures of the Taylor cavity interface propagation agrees well with the experimental value.