Computational Fluid Dynamics Models of Electromagnetic Levitation Experiments in Reduced Gravity

Electromagnetic levitation experiments provide a powerful tool that allows for the study of nucleation, solidification and growth in a containerless processing environment. Containerless processing allows for the study of reactive melts at elevated temperatures without chemical interactions or contamination from a container. Further, by removing the interface between the liquid and its container, this processing technique allows for greater access to the undercooled region for solidification studies. However, in these experiments it is important to understand the magnetohydrodynamic flow within the sample and the effects that this fluid flow has on the experiment. A recent solidification study found that aluminum-nickel alloy sample have an unusual response of the growth rate of the solid to changes in undercooling. This alloy experienced a decrease in the growth velocity as the initial undercooling deepened, instead of the expected increase in solidification velocity with deepening undercoolings. Current work is exploring several different theories to explain this phenomenon. Distinguishing among these theories requires a comprehensive understanding of the behavior of the internal fluid flow. Our project, USTIP, has done flow modeling to support this and multiple other collaborators on ISS-EML. The fluid flow models presented for the aluminum-nickel sample provide critical insights into the nature of the flow within the aluminum-nickel alloy experiments conducted in the ISS-EML facility. These models have found that for this sample the RNG k-ε model should be used with this sample at temperatures greater than 1800 K and the laminar flow model should be used at temperatures lower than 1600 K. Other work in the ISS-EML, has studied the thermophysical properties of liquid germanium and has found the most recent measurements using oscillating drop techniques to have a discrepancy from the expected property measurements taken terrestrially. Investigating this discrepancy required the quantification of the velocity and characterization of the internal fluid flow in the drop. The models have found that the flow within the sample maintains turbulent behavior throughout cooling. This thesis presents the analysis of the internal flow of four additional samples processed in the International Space Station Electromagnetic Levitation facility. These samples consist of the following alloys: Ti39.5Zr39.5Ni21, Cu50Zr50, Vitreloy 106, and Zr64Ni36. Our collaborators work required the internal flow to be characterized and quantified for their work on solidification. In addition to quantifying the velocity of the flow, the Reynolds number was calculated to characterize the flow during processing. Additionally, the shear-strain rate was calculated for the flow during processing up to the recalescence of the melt

Effects of Oxygen Partial Pressure on the Surface Tension of Liquid Aerospace Alloys

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Electrostatic Levitation for Studies of Materials for Additive and In-Space Manufacturing

The electrostatic levitation (ESL) laboratory at NASA's Marshall Space Flight Center (MSFC) is a unique facility for investigators studying high-temperature materials. Electrostatic levitation minimizes gravitational effects and allows materials to be studied without contact with a container or instrumentation

SOLIDIFICATION EXPERIMENTS AND MAGNETOHYDRODYNAMIC MODELS IN ELECTROMAGNETIC LEVITATION

Electromagnetic levitation (EML) is a technique for containerless processing. The unique environment of containerless processing allows for the study of highly reactive melts at elevated temperatures. In containerless processing, the interface between a melt and its container is removed, reducing chemical contamination. In addition, levitation techniques reduce the available heterogeneous nucleation sites, providing greater access to the undercooled region for solidification studies. Levitation techniques provide the environment to study the fundamental behavior and thermophysical properties of liquid metals. During electromagnetic levitation experiments, magnetohydrodynamic flow is driven in the sample by the electromagnetic force field. This flow can have various effects on the sample, some of which are detrimental to measurements. In other experiments the internal flow is an experimental variable that is necessary to interpret the experimental results. However, the flow in most metallic melts is difficult to directly measure because metallic melts are opaque and featureless, while also quickly dissolving any tracer particles. Since the flow in the sample is not possible to measure directly from the experimental observations, computational fluid dynamics (CFD) is used to calculate the flow using the experimental conditions present at the point of interest for a given experiment. The work presented here contributes to the steady-state models used to calculate the flow resulting from the EML force field. The current model presented here is validated both against an experimental case and against previous published models. During development of the new models, variations across different versions of ANSYS Fluent were observed. The differences were explored and found to be within an acceptable range. The steady-state model was applied to a series of parabolic flight experiments on Fe-10wt\%Si. Additionally, the steady-state model was used to calculate the flow conditions on a zirconium sample at the time of anomalous solidification events observed during ISS-EML experiments. The steady-state model was expanded to a transeint model to further explore the flow effects on the sample. By developing a transient model, the effects of the excitation pulse on the internal flow was calculated for a $Zr_{64}Ni_{36}$ sample. This sample was observed to experience pulse-triggered solidification. The transient model provided insights into behavior of the internal flow at the time of solidification

Thermophysical properties of the TiAl-2Cr-2Nb alloy in the liquid phase measured with an electromagnetic levitation device on board the International Space Station, ISS-EML

Thermophysical properties of the γ-TiAl alloy Ti-48Al-2Cr-2Ni in the liquid phase were investigated with a containerless electromagnetic processing device on board the International Space Station. Containerless processing is warranted by the high liquidus temperature Tliq = 1 776 K and the high dissolution reactivity in the liquid phase. Thermophysical properties investigated include the surface tension and viscosity, density, specific heat capacity and the electrical resistivity. The experiments were supported by magnetohydrodynamic fluid flow calculations. The Ti-48Al-2Cr-2Ni alloy could be stably processed over extended times in the stable and undercooled liquid phase and exhibited an exceptional degree of undercooling before solidification. Experimental processes and thermophysical properties so obtained will be described. The experiments demonstrate the broad experimental capabilities of the electromagnetic processing facility on the International Space Station for thermophysical investigations in the liquid phase of metallic alloys not achievable by other methods