Laser-induced two-dimensional periodic and chaotic motions on molten tantalum and molybdenum surfaces

Abstract

Two-dimensional flow patterns generated in high-power short-time laser–material interaction on the vapourizing surface of tantalum and molybdenum have been studied. The inhomogeneous pattern of turbulent cells was divided into homogeneous zones (basins) of dynamics which form characteristic streamline patterns. They were simulated by using the model of regular and chaotic flow of Boldrigini and Francheschini, based on the real-mode truncation of the Navier–Stokes equation in k space. The nine-mode model with three-mode forcing reproduced the characteristic 'footprint' cells, triangular cells, 'potato-like' cells and square cells for the Reynolds numbers Re = 80, 100 and 110, appearing in various basins with time delay with respect to the beginning of the laser pulse. All the basins show chaotic fluid motion in the Eulerian picture, and the motion changing from regular to chaotic in the Lagrangian picture.