Numerical Simulation and Analysis on Velocity Profiles of Jet Projectile Charge

Jet projectile charge （JPC） is a relatively new type of perforating jet mainly used for defeating concrete targets. Velocity profile is an important parameter to investigate the penetration and performance of JPC. Since limited information such as X-ray radiographs and penetration depth can be obtained through the JPC experiment, the numerical simulation and further methodology are needed to depict the mechanism of JPC. This paper describes a mathematical approach based on Matlab to determine JPC velocity profile at various stand offs using three sets of jet data from numerical simulations. X-ray radiographs experimental results have been obtained at two time instants for two selected JPC design to verify the numerical accuracy. The velocity profiles by mathematical approach and simulation show good accordance. The number of experiments can be reduced by numerical simulation and analysis of velocity profiles. This approach can be generalized to any such system where explosive-metal interaction results in formation of jets.

Numerical study of the influence of dielectric tube on propagation of atmospheric pressure plasma jet based on coplanar dielectric barrier discharge

A 2D fluid model was employed to simulate the influence of dielectric on the propagation of atmospheric pressure helium plasma jet based on coplanar dielectric barrier discharge（DBD）.The spatio-temporal distributions of electron density,ionization rate,electrical field,spatial charge and the spatial structure were obtained for different dielectric tubes that limit the helium flow.The results show that the change of the relative permittivity of the dielectric tube where the plasma jet travels inside has no influence on the formation of DBD itself,but has great impact on the jet propagation.The velocity of the plasma jet changes drastically when the jet passes from a tube of higher permittivity to one of lower permittivity,resulting in an increase in jet length,ionization rate and electric field,as well as a change in the distribution of space charges and discharge states.The radius of the dielectric tube has a great influence on the ring-shaped or solid bullet structure.These results can well explain the behavior of the plasma jet from the dielectric tube into the ambient air and the hollow bullet in experiments.

Detached eddy simulation on the structure of swirling jet flow field

The improved delayed detached eddy simulation method with shear stress transport model was used to analyze the evolution of vortex structure,velocity and pressure fields of swirling jet.The influence of nozzle pressure drop on vortex structure development and turbulence pulsation was investigated.The development of vortex structure could be divided into three stages:Kelvin-Helmholtz(K-H)instability,transition stage and swirling flow instability.Swirling flow could significantly enhance radial turbulence pulsation and increase diffusion angle.At the downstream of the jet flow,turbulence pulsation dissipation was the main reason for jet velocity attenuation.With the increase of pressure drop,the jet velocity,pulsation amplitude and the symmetry of velocity distribution increased correspondingly.Meanwhile the pressure pulsation along with the axis and vortex transport intensity also increased significantly.When the jet distance exceeded about 9 times the dimensionless jet distance,the impact distance of swirling jet could not be improved effectively by increasing the pressure drop.However,it could effectively increase the swirl intensity and jet diffusion angle.The swirling jet is more suitable for radial horizontal drilling with large hole size,coalbed methane horizontal well cavity completion and roadway drilling and pressure relief,etc.

Controllable diameter of electrospun nanofibers based on the velocity of whipping jets for high-efficiency air filtration

Electrospun nanofibers are regarded as a promising candidate for filtration because of their prominent size effect.The precise control of nanofiber diameter is the key to the material’s outstanding filtration capability,but it remains a challenge.Herein,an electrohydrodynamic scaling model is established for the accurate prediction of fiber diameter based on the velocity of the whipping jet.In this model,the velocity reflects jet stretching and is tuned by adding salt.The theoretical predictions agree well with the experimental results.With the proposed diameter model,the filtration property of the membrane is significantly optimized by governing the fiber diameter.When the nanofiber is slenderized to 183 nm,an ultralight (0.521 g m;) membrane exhibits high filtration efficiency (99.93%) and low pressure drop (105.2 Pa) against ultrafine aerosol particles (≤0.26μm) under an airflow face velocity of 5.33 cm s^(-1).These findings demonstrate that the established surface charge-based diameter model provides an excellent platform to timely and accurately control the nanofiber diameter via the velocity of whipping jets for highefficiency air filtration.