The aerodynamic interaction between the airframe and engine are simulated using Computational Fluid Dynamics (CFD). Contrary to the common CFD approach, where the flow inside the engine is excluded from the computation, the flow is computed in the entire domain consisting of both the external airframe domain and the internal engine domain. This is done by using multiple frames of reference for solving the flow equations in each domain. By choosing a suitable frame of reference for each domain, the flow can be computed locally using a steady-state approximation. Communication between the domains takes place through the interfaces formed by the engine inlet and outlet. To ensure dependency between the solutions of the separate computational domains a Gauss-Seidel type iterative procedure was used. Each time a new solution is obtained for the airframe or engine domain, the interface conditions are updated and computations in the other domain are started. This procedure is iterated until convergence for the entire flow field is reached. At the interfaces non-reflecting boundary conditions for multiple reference frames are implemented. The resulting method is applied to a typical Airbus A-300 series aircraft model with two under-wing ultra high by-pass ratio engines with two counter rotating fans each.
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