Consistent boundary conditions for integrated LES/RANS simulations: LES outflow conditions

The numerical flow prediction of highly complex flow systems, such as the aero-thermal flow through an entire aircraft gas turbine engine, require the application of multiple specialized flow solvers, which have to run simultaneously in order to capture unsteady multi-component effects. The different mathematical approaches of different flow solvers, especially LES and RANS flow solvers, pose challenges in the definition of boundary conditions at the interfaces. Here, a method based on a virtual body force is proposed to impose Reynolds-averaged velocity fields near the outlet of an LES flow domain in order to take flow effects downstream computed by a RNS flow solver into account. This method shows good results in a test case of a swirl flow, where the influence of a flow contraction downstream of the LES domain is represented entirely by the Reynolds-averaged velocity Held at the outlet of the LES domain.