Interface instability of the thermal plasma jet

Abstract

This work is first focused to experimentally study the interface instability and expansion mechanism of thermal plasma jet and provide a better understanding of the complex fluid-dynamic interactions occurring on the surface of the plasma bubble due to the Kelvin–Helmholtz effect. The experimental techniques used include a plasma generator, a pulse-forming network based on the capacitive energy storage, pressure measurement system along the capillary tube, and high-speed camera system to trace the development processes of the plasma interface. Results indicate that the plasmas jet has a better advantage of radial expansion with a high light at the beginning. However, the axial expansion velocity is larger than the radial one with time going on; thus, a torch-shaped jet body occurs under the Rayleigh–Taylor effect and can be divided into two parts including a plasma head and tail. With a dissipation of the initial energy and turbulent mixing between the plasmas and the gas, the jet boundary is broken and even the local rupture phenomena occur on the plasma jet surface. The turbulent dissipation is also very violent when the discharge voltage increases to 3000 V; thus, the turbulent mixing layer between the plasma jet and the gas is quite thicker and the plasma jet boundary is also fuzzy resulting in that the fold surfaces with much larger degree exist earlier. These experimental phenomena are also explained further from the mechanism by deriving the momentum equations of the interface of the plasma jet into the gas. Finally, a fitting formula of the surface area as an important factor in the expansion process of the plasma is obtained to analyze the interface characteristic of the plasma jet.