Maximisation of installed net resulting force through multi-level optimisation of an ultra-high bypass ratio engine nacelle

Engine/wing interference in podded installations can introduce relevant changes to their isolated behaviour, especially for large turbofans with an ultra-high bypass ratio. With such coupled flow field, the interaction is best described by the integrated force acting on the whole aircraft. Rather than focusing on drag or thrust metrics separately, in this paper we maximise the net resulting force on the NASA CRM wing body with underwing-installed turbofans through a multi-level optimisation procedure of the engine nacelle. The first stage involves two-dimensional axisymmetric geometries for cowl and exhaust ducts shapes optimisation. The solutions are transformed into three-dimensional nacelles with pylon, featuring a non-axisymmetric inlet. The impact of the pylon on the exhaust flow is evaluated through a design of experiment and a successive surrogate-based optimisation. In the last step, nacelle/wing offset, intake angles, and engine orientation are assessed in the installed configuration at fixed lift. The final optimised design is compared with a baseline geometry initially defined, showing a significant improvement of the net vehicle thrust equal to 3% of the reference force. The result highlights a counteracting effect of individual force components, in a way that the installed resulting force can only be improved when considering them globally.