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Investigation into Flow Field in Relation to Laser Gas Assisted Processing: Influence of Assisting Gas Velocity on the Flow Field

A transiently developing jet finds application in metal processing, such as a vapor jet produced during laser ablation of solid surfaces. In the present study, laser gas-assisted processing is considered and vapor ejection from the solid surface during the ablation process is modeled. In this case, a transiently developing jet emerging from the solid wall and steady jet opposing (impinging onto) the transiently developing jet situation is studied. Since the thermal properties of vapor ejecting from the wall is not known, transiently developing helium jet is considered to resemble the vapor emanating from the wall. An air jet is employed to impinge onto the developing jet. The transient flow properties of the developing jet are obtained from the previous study. The flow and temperature fields are predicted numerically using a control volume approach. A low Reynolds number k–ϵ turbulence model is used to account for the turbulence. In order to investigate the influence of mean velocity of the steady jet on the flow field near the transiently developing jet, four mean velocities are considered. It is found that mean velocity of the steady jet has significant effect on the flow field in the region close to the transiently developing jet. In this case, a circulation cell is developed next to the steady jet boundary and the orientation of cell is influenced by the steady jet flow conditions.