Calculated transient two-dimensional Marangoni flow in a pulsed-laser weld pool

Pulsed-laser welding produces short-lived weld pools which have strong radial temperature gradients at the pool surface. These gradients produce surface tension variations which usually reinforce the weak natural convective flows caused by radial temperature gradients. The flow in the molten pool is of interest because it can change the temperature distribution in and around the molten zone which can alter the weld shape, and because it controls the transport of surface contaminants (or alloying or doping materials in case of surface processing) into the substrate. A two-dimensional finite difference code is being developed to model the transient flow in a prescribed axisymmetric weld pool geometry. A flux corrected transport algorithm is used with a vorticity-steamfunction formulation of the problem to calculate the flow field. Flow velocities during a typical laser pulse are presented for nickel and steel.