This paper describes extensions and tests of characteristicmethods for outlet bound- ary conditions in compressible solvers. Three methods based on the specification of ingoing waves using one- and multi-dimensional approximations are extended to un- structured grids. They are first compared for weak to strong vortices propagating on low to high speed mean flows through outlet sections. A major issue is to determine theMach number to be used in the specification of the transverse terms which must be taken into account in the ingoing wave amplitude specifications. For the vortex com- putations, results show that the averaged Mach number leads to better results than its local value. The boundary conditions are then tested in a more complex case: the flow around a turbine blade. A reference solution using a long distance between the blade trailing edge and the outlet plane is first computed: for this solution, outlet boundary conditions have almost no effect on the flow around the blade.
Granet, V., Vermorel, O., Léonard, T., Gicquel, L., & Poinsot, T. (2010). Comparison of Nonreflecting Outlet Boundary Conditions for Compressible Solvers on Unstructured Grids. AIAA Journal, 48(10), 2348–2364. https://doi.org/10.2514/1.J050391