Analysis of installation aerodynamics and comparison of optimised configuration of an ultra-high bypass ratio turbofan nacelle

The installation aerodynamics of ultra-high bypass ratio turbofan engine nacelles involves a strong interaction with the wing and a complex dependency of the forces from the geometric assembly. In the paper, we present a detailed numerical analysis of the flow field and the propulsive metrics for a baseline and an optimised nacelle model mounted under the NASA Common Research Model wings at cruise condition. The wing/nacelle offset represents the main parameter affecting the resulting performance for a given nacelle shape. An extended range of positions is first examined at constant lift, showing the existence of a local maximum for the net resulting force and a larger sensitivity to the horizontal displacement. The installation effect results much stronger on the inboard side with a relevant coupling caused by potential interaction, flow channelling under the wing, and jet/wing interference. The reference baseline nacelle is compared with a sample optimised for the maximum installed net resulting force, analysing local force distributions bringing the overall improvement. Finally, a newly developed automatic procedure to achieve a zero net resultant in numerical simulations is applied. By using an equivalent shaft power, the optimised nacelle is found to provide a 1.79% saving, estimated to amount to a 0.98% fuel burn reduction in the cruise operating point considered.