Numerical Simulation of Gas Jet Effects in Laser Machining

In this paper, the interaction of a transonic, turbulent axisymmetric jet with the workpiece is studied. Numerical simulations are carried out using an explicit, coupled solution algorithm with solution-based mesh adaptation. Effect of gas pressure and nozzle standoff distance on structure of the supersonic shock pattern is studied. Experiments are carried out to study the effect of processing parameters such as gas pressure and standoff distance. The measured results match and hence validate the simulations. The interaction of the oblique incident shock with the normal standoff shock is found to contribute to a significant reduction in the total pressure at the machining front when the nozzle pressure increases beyond a certain point. The associated reduction in flow rate, fluctuations of pressure gradient and shear force at the machining front could lower the material removal capability of the gas jet and possibly result in a poorer surface finish. A Co D area of delivery nozzle exit nozzle discharge coefficient nozzle exit diameter m mass flow rate p static pressure Nomenclature Am d H M P. total gauge pressure at nozzle exit Pt R To p y T temperature V m velocity at measurement nozzle exit Pm density at measurement nozzle exit subscripts for m n delivery nozzle m h hole