Modeling of Temperature Dependent Surface Tension Forces Validation of a Temperature Dependent Surface Tension Framework with Application to Powder Bed Melt Pool Dynamics
Ladda ner
Typ
Examensarbete för masterexamen
Master Thesis
Master Thesis
Program
Applied mechanics (MPAME), MSc
Publicerad
2019
Författare
Nilsson, Victor
Modellbyggare
Tidskriftstitel
ISSN
Volymtitel
Utgivare
Sammanfattning
One of the challenges with CFD simulations of metal AM is to properly model the temperature dependent surface tension force driving the melt pool flow. High density ratio multiphase flows, as between the gas and the liquid metal in melt pool flow, are considered difficult to model due to the generation of spurious currents at the interface. At Fraunhofer Chalmers Center (FCC) a state-of-the-art CFD solver, IBOFlow is developed. In this project the existing surface tension framework in IBOFlow is improved and extended. A temperature dependent surface tension model together with a thermo-capillary force is proposed. The new surface tension framework is assessed and validated so that the melt pool dynamics of metal AM is accurately modeled. Different curvature estimation techniques and a technique for calculating the interface normal direction are thoroughly tested and evaluated in order to reduce the influence of spurious currents on the results. The numerically calculated curvature and pressure is evaluated and validated against analytical results for a case involving a static droplet in equilibrium. Further more a temperature dependent surface tension model is also proposed and validated together with a thermo-capillary surface tension force. The benchmark case to evaluate the temperature dependent surface tension and the thermo-capillary surface tension force include a comparison with thermo-capillary cavity flow. The result of the static droplet case show a substantial improvement when calculating the interface curvature and pressure difference across the interface, with results in line with exact analytical calculations. Furthermore, these improvements also substantially reduce the spurious currents around the interface. The temperature dependent surface tension model and the thermo-capillary surface tension force are validated against an analytical solution and compared to other numerical results of the thermo-capillary cavity flow. The results show perfect agreement with analytical values and outperform other numerical studies on the subject. The improved and extended surface tension framework is then used to demonstrate simulate a single line melt of a selective laser melting process on a powder bed.
Beskrivning
Ämne/nyckelord
Strömningsmekanik och akustik , Hållbar utveckling , Materialvetenskap , Fluid Mechanics and Acoustics , Sustainable Development , Materials Science