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Marangoni Driven Turbulence in High Energy Surface Melting Processes

Marangoni Driven Turbulence in High Energy Surface Melting Processes, Anton Kidess, Sasa Kenjeres, Bernhard W. Righolt, and Chris R. Kleijn. International Journal of Thermal Sciences 2016, 104 , 412–422.

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Abstract

Experimental observations of high-energy surface melting processes, such as laser welding, have revealed unsteady, often violent, motion of the free surface of the melt pool. Surprisingly, no similar observations have been reported in numerical simulation studies of such flows. Moreover, the published simulation results fail to predict the post-solidification pool shape without adapting non-physical values for input parameters, suggesting the neglect of significant physics in the models employed. The experimentally observed violent flow surface instabilities, scaling analyses for the occurrence of turbulence in Marangoni driven flows, and the fact that in simulations transport coefficients generally have to be increased by an order of magnitude to match experimentally observed pool shapes, suggest the common assumption of laminar flow in the pool may not hold, and that the flow is actually turbulent. Here, we use direct numerical simulations (DNS) to investigate the role of turbulence in laser melting of a steel alloy with surface active elements. Our results reveal the presence of two competing vortices driven by thermocapillary forces towards a local surface tension maximum. The jet away from this location at the free surface, separating the two vortices, is found to be unstable and highly oscillatory, indeed leading to turbulence-like flow in the pool. The resulting additional heat transport, however, is insufficient to account for the observed differences in pool shapes between experiment and simulations. (C) 2016 Elsevier Masson SAS. All rights reserved.

BibTeX

@article{ ISI:000376696700036,
Author = {Kidess, Anton and Kenjeres, Sasa and Righolt, Bernhard W. and Kleijn, Chris R.},
Title = {Marangoni Driven Turbulence in High Energy Surface Melting Processes},
Journal = {International Journal of Thermal Sciences},
Year = {2016},
Volume = {104},
Pages = {412-422},
Month = {},
Abstract = {Experimental observations of high-energy surface melting processes, such as laser welding, have revealed unsteady, often violent, motion of the free surface of the melt pool. Surprisingly, no similar observations have been reported in numerical simulation studies of such flows. Moreover, the published simulation results fail to predict the post-solidification pool shape without adapting non-physical values for input parameters, suggesting the neglect of significant physics in the models employed. The experimentally observed violent flow surface instabilities, scaling analyses for the occurrence of turbulence in Marangoni driven flows, and the fact that in simulations transport coefficients generally have to be increased by an order of magnitude to match experimentally observed pool shapes, suggest the common assumption of laminar flow in the pool may not hold, and that the flow is actually turbulent. Here, we use direct numerical simulations (DNS) to investigate the role of turbulence in laser melting of a steel alloy with surface active elements. Our results reveal the presence of two competing vortices driven by thermocapillary forces towards a local surface tension maximum. The jet away from this location at the free surface, separating the two vortices, is found to be unstable and highly oscillatory, indeed leading to turbulence-like flow in the pool. The resulting additional heat transport, however, is insufficient to account for the observed differences in pool shapes between experiment and simulations. (C) 2016 Elsevier Masson SAS. All rights reserved.},
DOI = {10.1016/j.ijthermalsci.2016.01.015},
ISSN = {1290-0729},
EISSN = {1778-4166},
Unique-ID = {ISI:000376696700036},
}

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