High-fidelity simulations of liquid-gas-solid interactions during liquid metal casting processes

  • Qiao, Jiazhen (University of Maryland, College Park)
  • Riaz, Amir (University of Maryland, College Park)
  • Balaras, Elias (George Washington University)

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Non-metallic inclusions, known as dross or slag, have always remained problematic in the mechanical quality of metal castings. In particular, the endogenous inclusions which are formed during the filling of a casting from the oxidation of the liquid metal free surface and then stirred into the liquid metal by turbulent mixing are the most difficult to control: once formed, they cannot be separated and become permanent in the casting. Careful design of the casts to permit agglomeration of non-metallic inclusions to certain areas for easier removal during post processing is a typical strategy to alleviate the problem. The current generation of design tools, however, is correlation driven resulting in large uncertainties which increase the overall cost. There are several casting alloys that are sensitive to oxidation, which are widely used to form parts in many industries. The preset work focuses on the initial stages of dross formation related to the interaction of the laminar/turbulent jet impinging on a free surface. In the presence of air a thin metal oxide layer forms on the surface of the liquid changing the dynamics of the jet as well as and the resulting air-entrainement. To better understand the underlying physics we extended our high-fidelity, two-phase flow solver for incompressible flows to include the thin, highly deformable film that is formed on the liquid-gas interface. The frequent breakups of this oxidized layer render classical fluid-structure interaction methods where the solid is considered in a Lagrangian reference frame impractical. To address this issue we developed a fully Eulerian approach to model the liquid-gas-solid interactions. In particular, we use level set formulations to track both fluid-solid interfaces and the strain history of the deformable solid. The latter is accomplished by constructing a dynamic grid using three reference level set functions (one for each dimension) advected by the local velocity field. A unified framework is used to solve the equations governing the fluid and solid dynamics on the same fixed grid. Across the interface the shear modulus transitions smoothly from the bulk shear modulus to zero in a few computational cells. In the full paper we will discuss the cases of a jet impinging on a free-surface and air bubbles with an oxidized interface interacting with homogeneous turbulence in a liquid.