Comparison of nacelle models for the evaluation of an ultra-high bypass engine aerodynamics

The design of compact nacelles for ultra-high bypass engines is a complex task that must address several operating points and constraints. The typical workflow begins from twodimensional axisymmetric analysis and post-checks the three-dimensional geometries derived in the installed configuration. The nonuniform flow and pressure fields arising during the installation alter the isolated nacelle performance and the finally obtained design might be suboptimal. The paper considers four nacelle models, from two-dimensional axisymmetric to isolated three-dimensional nacelle with pylon and installed case. Each model is simulated using computational fluid dynamics and the aerodynamic forces are extracted and separated into drag and thrust components. They are then compared to highlight which terms are most varying from the simplest to the most complete configuration. The similarity between the nacelle cowl flows is also assessed. The three-dimensional geometry and the incidence effects alter the pressure fields from the axisymmetric simulations. We show that the 3D solution can be decomposed into a series of 2D axisymmetric problems run with an updated inlet mass flow. The study suggests that it is possible to anticipate some 3D-related phenomena in axisymmetric computations, thus possibly achieving a more accurate prediction of the 3D flow field and a more efficient design strategy.