On DEM-CFD study of the dynamic characteristics of high speed micro-abrasive air jet

In production technology, abrasive particles are increasing being utilised in abrasive jet micromachining. Despite of the many phenomenological investigations, the resolution of the flow field and the description of physical interactions between the carrying and abrasive media have not been thoroughly understood. In this paper, a discrete element method-computational fluid dynamics (DEM-CFD) analysis is performed to better understand the dynamic characteristics of high speed abrasive air jet. Abrasive particles of micron sizes within the air jet are examined to determine the jet evolution and expansion as well as the particle distribution within the flow. In particular, particle sphericity (shape factor) is considered for the particle-fluid interaction in addition to the particle-particle collision. Air and particle velocities for the flow downstream from the nozzle exit are simulated under transient, turbulent, two-phase flow conditions and different inlet conditions. Simulations of the particle flow characteristics using a range of particle shape factors are compared against experimental data with different inlet pressures and nozzle diameters. It is found that the predicted results agree well with the experimental data with particle shape factors of 0.6 and 0.8, which correspond to "edged" and "rounded" abrasive particles. With the consideration of lower shape factors, the increased in the aerodynamic drag resulted in higher particle velocities that allows the abrasive particles to remain more centrally along the centreline of the jet axis, and in turn affects the jet expansion. Nevertheless, the shape factors of the abrasive particles have been found to exert no discernible effect on the high speed air flow. It is also shown that the variation of nozzle sizes has a negligible effect on the maximum air velocities.