Outflow Conditions for Intregrated Large Eddy Simulation/Reynolds-Averaged Navier-Stokes Simulations

The numerical flow prediction of highly complex flow systems, such as the aerothermal flow through an entire aircraftgasturbineengine,requirestheapplicationofmultiplespecializedflowsolvers,whichhavetorunsimultaneously in order to capture unsteady multicomponent effects. The different mathematical approaches of different flow solvers, especially large eddy simulation (LES) and Reynolds-averaged Navier‐Stokes (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 downstream flow effects computed by a RANS flow solver into account. This method shows good results in the 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 field at the outlet of the LES domain. I. Motivation N UMERICALsimulationsofcomplexlarge-scaleflowsystems must capture a variety of physical phenomena in order to predicttheflowaccurately.Currently,manyflowsolversarespecialized to simulate one part of a flow system effectively, but are either inadequate or too expensive to be applied to a generic problem. Asanexample,theaerothermalflowthroughagasturbineengine can be considered. In the compressor and the turbine section, the flow solver has to be able to handle the moving blades, model the wall turbulence, and predict the pressure and density distributions properly. This can be done efficiently by a flow solver based on the Reynolds-averaged Navier‐Stokes (RANS) approach. On the other hand, the flow in the combustion chamber is governed by largescale turbulence, complex mixing processes, chemical reactions, and the presence of fuel spray. Experience shows that these phenomena require an unsteady approach. 1 Hence, the use of a large