Aerodynamic Installation Effects of Over the wing Mounted Ultra high bypass Engines

Paper in proceeding, 2022

In order to increase propulsive efficiency and decrease specific thrust, future aeroengines for commercial airliners will have to operate with higher bypass ratios and lower fan pressure ratios. This results in a substantial increase of the fan diameter. One major issue with the conventional under-wing installation of ultrahigh-bypass engines is the limited space underneath the wings. Integrating larger engines under-the-wings could require prohibitive increase in landing gear height and weight to attain an adequate ground clearance. One potential solution is to mount the engines over-the-wings, which would eliminate the ground clearance problem and, in addition, reduce ground noise. Over-wing nacelle installation acquired a bad reputation in the past since the benefits of such configuration would be often outweighed by poor aerodynamic performance. Nonetheless, some recent studies indicate that over-wing mounted nacelles could be a feasible integration option. This paper provides an aerodynamic evaluation of an over-the-wing mounted nacelle configuration compared with an under-the-wing configuration for a mid-cruise condition. The nacelles and pylons are designed by using an in-house tool for engine aircraft aerodynamic integration. The flow field is computed by means of Reynolds-averaged Navier-Stokes equations. The effects of wing/nacelle/pylon interference are investigated, and the aerodynamic performance of each configuration is evaluated by means of thrust and drag bookkeeping. Results show that the over-the-wing nacelle installation has increased the overall drag by 19.7 drag counts, when compared to a conventional under-wing mount, which was caused mainly due to a higher wing wave drag and pylon/nacelle interference drag.