EFFICIENT PREDICTION OF NACELLE INSTALLATION EFFECTS AT TAKE-OFF CONDITIONS

Nacelle installation aerodynamics is of significant importance for verifying the engine behavior at take-off, in presence of side winds and ground effects. These off-design conditions must be checked for eventual loss of power and for noise generation. While traditional CFD methods have been applied successfully to some of these problems such as ground effects, requiring however costly full unsteady simulations, the incorporation of the acoustic predictions is an additional challenge. The application of the nonlinear harmonic method (NLH) provides a highly efficient approach to simultaneously predict the unsteady aerodynamic ground effects around the nacelle as well as the distorted inlet flow in the fan, including the near field acoustic pressure waves. The paper summarizes the NLH methodology, which is applied to an integrated aero-engine including Fan, OGV (outlet guide vane) and nacelle intake in presence of ground effects and crosswind conditions. The meshing process responding to industrial constraints in resources and time is detailed. The development of the post-processing of the aerodynamic and noise spectra, derived from the NLH predictions, is presented, demonstrating that the NLH approach is able to simulate flow unsteadiness, inlet distortion and near field acoustics with a gain of several order of magnitudes in CPU time compared to traditional methods. NOMENCLATURE BPF Blade Passing Frequency DC60 Distortion Parameter = (Pt Pθ=±30°)/qt Vx lateral velocity Vy vertical velocity Vz axial velocity, with positive direction toward downstream direction Pt the average of total pressure at AIP. Pt0 the far-field total pressure Pθ=±30° Average minimal total pressure in the wedge zone of 60 degrees at the fan inlet plane PR Pressure Recovery = Pt/Pt0 qt Average dynamic pressure at AIP AIP Aerodynamic Interface Plane located at the fan face INTRODUCTION Take-off flight conditions represent a challenging flow behavior for aircraft engine inlets, which have to ensure uniform flow for fan or compressor blades, while the flow entering the inlet is not uniform due to: its nearness to the ground, the flight angle of attack when it starts to airborne, the presence of crosswind. The flow distortion generated at the lip area of an inlet must be recovered and smoothed at the plane just upstream of the fan to ensure safe engine operations. Moreover stringent environmental requirements dictate airport noise regulations.