Use of CFD Methods to Design Engine Nacelles

Abstract

The challenge for current and future nacelles of commercial engines is to obtain: -low transonic drag in cruise condition, -low weight and reduced dimensions without reducing the low speed operating domain (maximum incidence, crosswind, etc) and low noise level. This paper explains how various designs can be improved by using modern numerical methods. Concerning air inlets, 3D Euler code and boundary layer code are used for prediction of divergence Mach number and drag in cruise conditions. Low speed behaviour is also obtained for various flight conditions which cause high local incidences on air inlet sections. Attention is mainly focused on attached flow limits. CFD method calibrations based on existing tests results are needed for that work. Bypass and core nozzle design use axisymmetric Navier-Stokes calculations for the prediction of thrust and flow coefficients relative values. This calculation also helps on development of adequate designs of the throat region and provides detailed analysis of the core nozzle flowfield including interaction of outer cold jet. These methods are applied to the design of an advanced nacelle for a high bypass ratio engine. This nacelle is equiped with an original core cowl doors thrust reverser. Consequently the nacelle length and weight have been significantly reduced. The main numerical results obtained on this nacelle are presented including some results for the installation of this nacelle under a wing.