High-Fidelity Simulations of Interfacial Two-Phase Flows on Adaptive Unstructured Grids
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With the steady increase of the power of parallel super-computers, 3D unsteady simulations offer a great potential to study interfacial two-phase flows. However, the simulation of highly non-linear phenomena such as primary atomization requires very accurate numerical methods and high resolution to capture interface dynamics. While most direct numerical simulations of interfacial two-phase flows are carried out with structured grids or Cartesian-based Adaptive Mesh Refinement, recent advances in numerical methods for tetrahedron-based meshes and parallel mesh adaptation strategies raise the attractiveness of unstructured grids. The use of tetrahedra has two advantages for practical configurations: complex geometries are easily meshed and the mesh is locally more isotropic than Cartesian grids. The presentation will detail recent numerical improvements to the Accurate Conservative Level Set method (Janodet, 2022) in terms of interface distance, curvature calculation and profile reinitialization. The presentation will also discuss how to include more physics in such simulations such as static contact angles (Pertant, 2021) or scalar transport in order to widen the scope of these methods. Finally, the presentation will be focused on the development of highly-efficient dynamic adaptation of tetrahedron-based unstructured grids. The proposed methodology (Benard, 2016), which heavily relies on the remeshing library MMG (www.mmgtools.org) (Dapogny, 2014) has been thoroughly optimized to reach good performances with grids of several billion cells on more than 10 000 cores. This dynamic mesh adaptation strategy has been implemented in the YALES2 code (www.coria-cfd.fr) and applied to the modeling of primary atomization in many configurations: liquid jet in cross flow, pressure swirl atomizers, triple disk pressure injector, oil scavenging systems... In these applications, the local mesh adaptation enabled a drastic reduction of the CPU cost compared to the fixed-grid approach and enabled to reach unprecedented mesh resolutions at the interface.
