Investigation Of Plasma Jet Interaction With Bulk-Loaded Liquid Medium

Taking bulk-loaded liquid propellant electrothermal chemical gun as engineering background, experimental and theoretical studies on interaction characteristic the plasma jet with bulk-loaded liquid have been conducted. The control mechanism and method of combustion stability in BLPG are explored and the research results have an important value for guiding interior ballistic design of bulk-loaded liquid propellant electrothermal chemical gun. The main research contents and results are as follows:(1) Experimental study on plasma jet propagation in airA test platform on plasma jet expansion in atmosphere is designed. The testing system of transient pressure is used to measure the pressure in the capillary. The series processes of the plasma jet in atmosphere are recorded by means of a high-speed digital camera. The effects of discharge voltage and nozzle diameter on plasma jet are explored. The results indicate that:when the plasma jet expands in the air, the axial expansion velocity is greater than the radial expansion one. The plasma jet can be divided into two parts:cone-jet head and slender body of the jet. The cone-jet head is very bright. And turbulent mixing between plasma jet and air is very strong. When the discharge voltage increases, the brightness and the expansion displacement of the plasma jet all increase, but incremental decreases. As nozzle diameter is bigger, the expansion displacement of the plasma jet is larger.(2) Numerical simulation on plasma jet in atmosphereBased on the experiments, a two dimensional unsteady mathematical model is established, the process of plasma jet expansion in atmosphere is simulated by Fluent. The distribution properties of pressure, velocity, density and temperature in the plasma jet flow filed, and the interface evolution properties of plasma jet and air are obtained. The results show that, the Mach disk exists downstream at the beginning of jets and a tapered low velocity zone appears on the downstream zone of Mach disk. With the jets bifurcating, the hollow jet is gradually formed. As time goes on, the bifurcate jets begin to converge. The radial dimension of the jet first increases then decreases. The periodic pressure waves exist near the nozzle. The temperature, velocity and density are all pulsing along the axial direction. As a whole, the temperature and velocity increase progressively along the axial and radial direction. The simulated values of axial displacements of plasma jet coincide well with the experimental ones.(3) Experimental study on the interaction of plasma jet with liquid A test platform for plasma jet expansion in liquid was designed to study the interaction of plasma jet with liquid in cylindrical chamber and cylindrical stepped-wall chamber. Discussions focus on the effects of pressure, nozzle diameter and the structure factor of stepped-wall chamber on the expansion processes of plasma jets. The entrainment and backflow characteristics of plasma jet are analyzed. The results show that, the axial velocity is larger than radial one as the plasma jet expands in cylindrical chamber. In addition, the surface of Taylor cavity is more random and the Taylor-Helmholtz instability is more intense. However, in cylindrical stepped-wall chamber, Taylor cavity expands forward by step and step due to the induction effect of steps, which can weaken Taylor-Helmholtz instability effect along the axial direction and restrict randomness of gas-liquid interface. The pressure, nozzle diameter and the structure factor (AD/L) of stepped-wall chamber all affect the expansion process of plasma jet, so the expansion processes can be controlled by matching these parameters.(4) Numerical simulation of plasma jet expansion in liquidBased on the experiment, a two dimensional unsteady mathematical model was established and the process of plasma jet expansion in liquid is simulate by Fluent to obtain the distribution properties of pressure, velocity, density and temperature in the plasma jet flow filed, and the interface evolution properties of plasma jet with air. The results show that, as Taylor cavity is formed in expansion process of plasma jet, the axial velocity is larger than the radial one and the various parameters near the nozzle is pulsing along the axial direction. But the range of pulsation is smaller than expansion processes in the atmosphere. The necking phenomenon of plasma jet exists near the nozzle with liquid entrainment into Taylor cavity. The expansion processes of plasma je in liquid can divided into three flow zones:main stream zone, compression zone and backflow zone. When plasma jet expands in the cylindrical chamber, pressure waves basically are plane waves and the jet expands more slowly along radial direction. However, when plasma jet expands in the cylindrical stepped-wall chamber, pressure waves basically show cambered and the radial pressure gradient is larger. Compared with cylindrical chamber, the radial expansion velocity is bigger in the cylindrical stepped-wall chamber, and the backflow zone exists in the corners of each step.(5) Numerical simulation on ignition, combustion and propellant processes of plasma in BLPGThe two dimensional mathematical model is established and ignition, combustion and propellant processes of plasma are simulated to obtain to obtain the distribution properties of pressure, velocity, density and temperature, and the variation properties of gas-liquid interfaces. The results show that, pressure in the combustion chamber appears to pulse in bulk-loaded liquid propellant electrothermal chemical gun and thus pressure curve of the chamber shows multimodal distribution. Cylindrical stepped-wall chamber can help that combustion front expands progressively along the expanding steps, weakening the random in the combustion process and decreasing the Taylor-Helmholtz instability effect.