Modeling of Ti-W Solidification Microstructures Under Additive Manufacturing Conditions

Additive manufacturing (AM) processes have many benefits for the fabrication of alloy parts, including the potential for greater microstructural control and targeted properties than traditional metallurgy processes. To accelerate utilization of this process to produce such parts, an effective computational modeling approach to identify the relationships between material and process parameters, microstructure, and part properties is essential. Development of such a model requires accounting for the many factors in play during this process, including laser absorption, material addition and melting, fluid flow, various modes of heat transport, and solidification. In this paper, we start with a more modest goal, to create a multiscale model for a specific AM process, Laser Engineered Net Shaping (LENS™), which couples a continuum-level description of a simplified beam melting problem (coupling heat absorption, heat transport, and fluid flow) with a Lattice Boltzmann-cellular automata (LB-CA) microscale model of combined fluid flow, solute transport, and solidification. We apply this model to a binary Ti-5.5 wt pct W alloy and compare calculated quantities, such as dendrite arm spacing, with experimental results reported in a companion paper

Numerical study of convection induced by evaporation in cylindrical geometry

International audienceNumerical simulations of convection induced by solvent evaporation during the drying of a polymer solution are considered. This paper focuses on the transient thermal regime occurring at the beginning of the drying and transient solutal effects are not taken into account. The onset of convection (B'enard-Marangoni and Rayleigh-B'enard) is studied for a large range of initial thicknesses and viscosities. Several stochastic models are compared to analyze the influence of the perturbation description on the transition thresholds. Two-dimensional (2D) and three-dimensinal (3D) models are shown to give close results. The 3D model is used to characterize the pattern evolution during the drying. In the case of surface tension driven convection, a method is developed to describe the cells morphology and their time evolution

Uncertainty Quantification of Thermocouple Air Temperature Measurement in Highly Radiative Environment: Application to Turbofan Engine Compartment

This paper focuses on thermocouple air temperature measurement uncertainty due to the radiative fluxes present in the engine compartment where engine case skin temperature can exceed 900 K. To really measure air temperature, the convective heat flux in the thermocouple bead must be predominant. This is why heat shields are used in order to reduce the radiative heat flux on the bead. However, in engine compartment, the heat shield orientation must be optimized since numerous hot walls surround the thermocouple. In order to evaluate the impact of badly oriented heat shields and to provide a data bank for numerical simulation validations, a heated wind tunnel has been used. It has been shown that the uncertainty on the thermocouple temperature can reach dozens of degrees depending on the air speed and the heat shield orientation. Furthermore a specific 3D thermocouple model has been build and validated by comparison with the lab measurements. Then this thermocouple 3D model has been integrated in the whole engine compartment aero-thermal model in order to quantify the uncertainty of the thermocouple air temperature measurement in the real engine environment.</jats:p

Numerical study of convection induced by evaporation in cylindrical geometry

International audienceNumerical simulations of convection induced by solvent evaporation during the drying of a polymer solution are considered. This paper focuses on the transient thermal regime occurring at the beginning of the drying and transient solutal effects are not taken into account. The onset of convection (B'enard-Marangoni and Rayleigh-B'enard) is studied for a large range of initial thicknesses and viscosities. Several stochastic models are compared to analyze the influence of the perturbation description on the transition thresholds. Two-dimensional (2D) and three-dimensinal (3D) models are shown to give close results. The 3D model is used to characterize the pattern evolution during the drying. In the case of surface tension driven convection, a method is developed to describe the cells morphology and their time evolution

Transient Rayleigh-Bénard-Marangoni solutal convection

Solutal driven flow is studied for a binary solution submitted to solvent evaporation at the upper free surface. Evaporation induces an increase in the solute concentration close to the free surface and solutal gradients may induce a convective flow driven by buoyancy and/or surface tension. This problem is studied numerically, using several assumptions deduced from previous experiments on polymer solutions. The stability of the system is investigated as a function of the solutal Rayleigh and Marangoni numbers, the evaporative flux and the Schmidt number. The sensitivity of the thresholds to initial perturbations is analyzed. The effect of viscosity variation during drying is also investigated. At last numerical simulations are presented to study the competition between buoyancy and Marangoni effects in the nonlinear regime