Assessment of engine modelling on the installed aerodynamics of an ultra-high bypass turbofan

Installation effects on large turbofans with ultra-high bypass ratio derive from the complex three-dimensional pressure and flow fields arising in the integrated configuration. Standard powered-on modelling approaches in computational fluid dynamics simulations are based on uniformly prescribed boundary conditions on the engine entry and exit planes, derived from thermodynamic cycle analysis. The real boundary distributions, however, are sensitive to the engine/airframe coupling. In the paper, we compare the standard approach with a coupled engine model based on a body force method for the bypass stage, analysing three geometric configurations, from isolated nacelle to underwing installation, at Mach number 0.85 cruise with lift coefficient of 0.50. The results indicate that the distributions at the bypass stage entry and exit planes are all but uniform, but the standard model based on averaged quantities qualitatively replicates the flow field. With the same area-averaged values set at the engine boundaries, the force acting on single aircaft parts exhibit a certain variation. When the net resulting force is considered, the difference between the models is 1.93% in the 3D isolated nacelle with pylon and 0.2% in the installed configuration, relative to the nacelle net propulsive thrust.