Center for Turbulence Research Annual Research Briefs 2006 275 Integrated RANS/LES computations of turbulent flow through a turbofan jet engine By G. Medic, G. Kalitzin, D. You, M. Herrmann, F. Ham, E. van der Weide, H. Pitsch AND J. Alonso 1. Motivation and objectives The interaction between different components of a jet engine represents a very impor- tant aspect of the engine design process. Sudden mass flow-rate changes induced by flow separation and pressure waves, interaction of the unsteady wakes originating from the fan blades with the low-pressure compressor, high temperature streaks interacting with the first stages of the turbine are all complex unsteady phenomena that cannot be sim- ply accounted for through boundary conditions of a single component simulation. Only simulations that integrate multiple engine components can describe these flow features accurately. Today’s use of Computational Fluid Dynamics (CFD) in gas turbine design is usually limited to component simulations. The demand on the models to represent the large variety of physical phenomena encountered in the flow path of a gas turbine mandates the use of a specialized and optimized approach for each component. The flow-field in the turbomachinery portions of the domain is characterized by both high Reynolds numbers and high Mach numbers. The prediction of the flow requires the precise description of the turbulent boundary layers around the rotor and stator blades, including tip gaps and leakage flows. A number of flow solvers that have been developed to deal with this kind of problem have been in use in industry for many years. These flow solvers are typically based on the Reynolds-Averaged Navier-Stokes (RANS) approach. Here, the unsteady flow-field is ensemble-averaged, removing all the details of the small scale turbulence; a turbulence model becomes necessary to represent the effects of turbulence on the mean flow. The flow in the combustor, on the other hand, is characterized by multi-phase flow, intense mixing, and chemical reactions. The prediction of turbulent mixing is greatly improved using flow solvers based on Large-Eddy Simulations (LES). While the use of LES increases the computational cost, LES has been the only predictive tool able to simulate consistently these complex flows. LES resolves the large-scale turbulent motions in time and space, and only the influence of the smallest scales, which are usually more universal and hence, easier to represent, has to be modeled (Ferziger, 1996, and Sagaut, 2002). Since the energy-containing part of the turbulent scales is resolved, a more accurate description of scalar mixing is achieved, leading to improved predictions of the combustion process, as shown in Raman & Pitsch (2005). LES flow solvers have been shown in the past to be able to model simple flames and are currently being adapted for use in gas turbine combustors, e.g., Poinsot et al. (2001) and Constantinescu et al. (2003). In order to compute the flow in the entire jet engine, one needs to couple RANS and LES solvers. We have developed a software environment that allows a simulation of multi- component effects by executing multiple solvers simultaneously. Each of these solvers computes a portion of a given flow domain and exchanges flow data at the interfaces with