This paper deals with the design of an isolated axisymmetric nacelle for an Ultra-High Bypass Ratio (UHBR) engine. The intake, fan cowl, bypass duct and bypass nozzle are designed and optimized using a nacelle design system, established by combining an automated CFD analysis framework with an optimization algorithm. The optimization algorithm is based on an adaptive response surface methodology (RSM), which uses Kriging approximation to generate the surface model. The entire nacelle is parameterized using an intuitive Class shape transformation (iCST) approach. The optimization was conducted separately for the intake-cowl and exhaust system assuming minimal aerodynamic interactions between the two. The final optimized design had 26.9 Drag counts at cruise. The response surface was able to predict the cruise drag to 6% accuracy. The optimized bypass nozzle gave a maximum velocity coefficient (C V) of 0.9914 at a corresponding discharge coefficient (C D) of 0.995.

Even with different energy storage systems and power technologies of future aircraft, the thrust performance will be implemented with propulsors. In this context, the off-design nacelle behaviour – in particular for pure crosswind tests – becomes increasingly important especially for ultra-short nacelle designs due to their supposed drag and weight benefits [Peters and Rose (2015)]. In the upcoming years, several experimental tests at the Propulsion Test Facility (PTF) in Braunschweig are planned, to investigate the intake performance for different scale sizes and aspirated/powered test setups. As a starting point, two axisymmetric nacelles differing in intake length were designed and optimized at a representative full-scale fan diameter using an intuitive class/shape transformation based parametrization. The length was varied between L/D = 0.49 (classical design) and L/D = 0.36 (short design) with a minimum cruise drag design objective. The work flow of the optimization algorithm and nacelle parameter trends analysis are presented. Both intakes are scaled down to the testing rig’s diameter for the off-design analysis and a numerical setup and mesh density study are conducted. Through a detailed analysis of crosswind and scaling effects on the intake aerodynamics, the full-scale designs are modified to deliver a similar distortion behaviour for both designs by adapting the contraction ratio of the intakes. As a preparation for the upcoming tests, the numerical results of the local lip aerodynamics were analyzed for both intake designs showing, inter alia, that a decrease of the intake length increases the aerodynamic loading at the throat for the windward section.

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