Flow streamline based Navier–Stokes Characteristic Boundary Conditions: Modeling for transverse and corner outflows

Some limitations of three dimensional Navier–Stokes Characteristic Boundary Conditions (3D-NSCBC) are discussed for flows traveling in a direction that is oblique to the boundary. To limit errors generated at boundaries with flows having any arbitrary direction, it is proposed to organize the wave decomposition in a coordinate system that is attached to the local flow streamline crossing the boundary, because some modeled expressions are not frame independent. Compared to previous 3D-NSCBC, the modified strategy accounting for oblique waves is found to improve the outflow treatment for transverse outgoing vortices, up to vortices crossing an outflow corner. The method is also applied to an expanding laminar flame.

► Highlight current limitations of outflow treatments for transverse flows.
► Improve the flow acceleration prediction at characteristic outflows.
► Decrease flow distorsions at open boundary conditions.