Design of a shape-adaptive rotor for the reduction of BLI induced losses in the distorted flow regimes of a scaled turbofan fan rotor

Abstract

Within the Cluster of Excellence for Sustainable and Energy-Efficient Aviation SE2A, a blended wing body aircraft is investigated to improve efficiency and carbon emissions of future air transport. By embedding the aircraft engines on the top rear fuselage, parts of the aircraft’s wing boundary layer are ingested, which has the potential to further improve the engine’s propulsion efficiency. Through the ingestion of low momentum fluid, inflow distortion is induced and the fan rotor operates under increased flow incidence, when passing through the distorted flow regimes. To reduce the thereby arising efficiency and pressure ratio penalties in the aircraft engine, alternative design strategies for the fan stage are required. Within this investigation, an active shape morphing mechanism is introduced, which allows to temporarily adjust the fan blading when the fan rotor is exposed to distorted inflow conditions. By integrating piezoceramic actuators into the rotor blading, the blade staggering and turning can be adjusted with the goal to reduce flow incidence and deviation in the distorted flow regimes. For this investigation, the NASA rotor 67 is chosen as an initial test case and its performance under boundary layer ingestion (BLI) conditions is evaluated. For the shape morphing assessment, FEA morphing simulations are coupled with stationary CFD simulations of the actuated fan rotor geometries under distorted inflow. As the achievable deformations for the NASA rotor 67 are however too small to compensate for the strong distortion effects, a fan re-design is conducted. The re-design follows current ultra-high-bypass-ratio (UHBR) fan concepts with a particular focus on the shape-morphing capability of the rotor. Within this investigation the focus especially lies on three-dimensional design adaptions, such as a hub chord reduction as well as dihedral and sweep. By considering carbon fiber reinforced polymers (CFRP) as blade material, the impact of tailored blade architectures on the morphing behavior is additionally considered.