Aerodynamic Design and Experimental Investigation of Short Nacelles for Future Turbofan Engines

Licentiate thesis, 2020

To achieve a higher propulsive efficiency, and hence reduced fuel burn and emissions, the next generation turbofan engines are expected to have higher bypass ratios and lower fan pressure ratios. However, the larger the bypass ratio, the larger becomes the fan and thus the nacelle. The result is an undesired increase in weight and nacelle drag. For this reason, advanced nacelle designs with shorter inlets and exhaust nozzles are necessary, so that the attained performance benefits are not outweighed by the increased installation drag and weight.

This thesis presents a newly developed methodology for multi-point design of ultra-short nacelles. An integrated aerodynamic framework, based on parametric geometry generation and computational fluid dynamics (CFD) flow solutions was built and used for designing several ultra-short nacelle shapes and to evaluate their aerodynamic performance. The main design parameters and their influence in the flow field were investigated for the most critical operating conditions among the flight mission, such as cruise, high angle-of-attack (AoA) and crosswind. The aerodynamic performance of the designed nacelles was evaluated through a thrust and drag bookkeeping approach, and also by means of the distortion levels at the fan face.

Furthermore, this work summarizes the main results obtained in an experimental aerodynamic investigation of a powered turbofan nacelle, conducted at the Chalmers low-speed wind tunnel. The impact of the engine angle-of-attack and the mass flow ratio (MFR) on the nacellle aerodynamic performance was investigated.