Aerodynamic Design Optimization of Nacelle and Intake

Abstract

Design of nacelle and intake for an aero engine is highly complex and always a compromise between contradicting design goals. The intake has to provide air for the engine with minimal pressure loss at all flight conditions like take-off, cruise, approach, or crosswind. Further the airflow has to be evenly distributed to allow satisfying operation of the fan, and the nacelle should produce as less drag as possible. Taking this into account, the ideal lip shape alternates between thin to minimize drag during cruise and thick contour to cover the requirements at off-design conditions. To efficiently deal with these contradicting geometric design demands, a multi-objective optimization problem in 2D is defined. The major aim is to simultaneously minimize inner peak Mach number at off-design and outer peak Mach number at cruise conditions, i.e., two different flight conditions are taken into account which are evaluated in parallel. Three different parametric models are introduced to describe design changes, a first model, using superellipses and polynomials, a second one based on Class-Shape-Transformation, and a B-spline approach. To check the robustness of the design process, design of experiments for all three parameterization approaches have been performed. Based on these results proper design bounds are derived to ensure reliable CAD model generation, meshing and CFD analysis. Optimization results from a multi-objective genetic algorithm demonstrate feasibility of the proposed approach. Compared to an existing design based on human experience, the designs found are better with respect to both objectives.