Nacelle: Air Intake Aerodynamic Design and Inlet Compatibility

Abstract

One of the most challenging operating conditions to be certified for FAR33 & FAR25 requirements is ground crosswind condition. When “Engine” is operated using the designed inlet and nacelle, within the flight envelope, could accommodate inlet separation/distortion resulted from crosswind and high angle-of-attack operating conditions. Inlet flow separation and distortion could trigger fan or core stall, as well as induce high fan and/or engine vibrations. The air induction system or inlet of the engine is designed to provide velocity and pressure distributions with minimum distortion and maximum pressure recovery to the propulsion system. Engine-inlet-airframe compatibility is one of the major tasks required to be evaluated in detail during the engine developing phase. This research is a parametric study of using CFD to evaluate operational characteristics of the air induction system. Comparisons of various inlet designs are made and characterized into three categories, i.e., i) Inlet flow recovery, ii) Inlet flow distortion, iii) Inlet Mach distribution. The objective is to assess the impact of air induction design of turbofan upon inlet compatibility. The current research work includes four parts, i.e., i) A geometry modeling process of nacelle, inlet, wing and fuselage, ii) A meshes generator ICEM, iii) The ANSYS CFX CFD software which could achieves numerical simulation and post-processing, iv) The Matlab platform with the function of coupling all considerations listed above for inlet compatibility optimization, based on genetic algorithm and Kriging agent model. The research introduces the Kriging model and weighting coefficient to optimize total pressure loss coefficient and static pressure recovery coefficient, with the external nacelle flow ignored. Bezier equation was used to fit the optimized curves obtained by changing two control points at the inter surface of nacelle. The wing-mounted model coupled with the nacelles, fuselage and wings was then built to make the assessment of inlet compatibility of air intake system relative to the isolate model. Comparison of aerodynamic performance was then made between the original and optimal nacelle, to show correlation between inlet compatibility and air intake profile.