Aerodynamic Aspects of Propulsion Integration for Next-generation Commercial Aircraft

Doctoral thesis, 2023

Propulsion integration is one of the most challenging aspects of aircraft design. It requires a multidisciplinary approach involving aerodynamics, propulsion, structures, weight, noise, and control systems. The constant push for lowering fuel burn and noise, and the recent goals for radically reducing the environmental impact of aviation drive the aviation industry to improve state-of-the-art technology and investigate innovative engine/aircraft integration solutions. A way to improve the specific fuel consumption of aircraft engines is by lowering the fan pressure ratio and increasing the bypass ratio. This is accompanied by larger fan diameters, and consequently increased nacelle weight and drag. The next-generation transport aircraft will feature engines substantially larger than those in-service, which will require shorter and lighter nacelles so that the engine performance benefits are not outweighed by an increased nacelle weight and drag. In this thesis, this problem is approached by developing new methods for the aerodynamic design of conventional and ultra-short nacelles, following a multi-point design methodology that considers the most critical operating conditions within the flight envelope. A computational fluid dynamics-based framework has been built to design nacelles and evaluate their aerodynamic performance. A comprehensive analysis of the aerodynamic aspects of nacelle design and the main parameters for the design of ultra-short nacelles are identified.

The installation of next-generation high-bypass turbofan engines also poses a major challenge to the aviation industry due to the limited space beneath the wings and stringent ground clearance constraints. Over-wing installed nacelles can be a potential solution for this problem, instead of the customary under-wing mounts. In this thesis, a framework for engine/aircraft integration aerodynamic design has been developed. The over-wing configuration is compared to conventional under-wing mounts in terms of aerodynamic performance. A novel method for wing redesign in the presence of the nacelle is proposed and an engine placement study is carried out.

In addition, low-speed wind tunnel tests were conducted for two scale configurations. The first was a standalone powered nacelle whereas the second was a half-span powered over-wing mounted nacelle configuration. The aim was to investigate the impact of the engine power setting and angle of attack on the flow field for low-speed operating conditions.