Development of Aspirated Ultra-Short Intakes for Aerodynamic Off-Design Analysis

Abstract

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.