Design and Performance of a Scaled Low Hub-to-Tip Ratio Turbofan Rotor with Shape-Morphing Capability

Abstract

New aircraft propulsion architectures increasingly rely on the turbofan as the main thrust generating component. Improving turbofan efficiency is therefore a promising approach to boosting overall propulsive efficiency, and thereby enhancing the sustainability of future aircraft engine architectures. Although current turbofans already operate at high on-design efficiencies, the engine and mission specific operating line determines operating periods with increased losses. To improve off-design operation, variable systems are increasingly investigated. As an alternative to pitch variable fan blading and variable nozzle geometries, this research proposes shape-adaptive fan blading. Applying piezoelectric Macro Fiber Composite actuators to the fan blades allows for an adjustment of the span-wise twist and turning of the rotor to match the inflow and flow deflection requirements occurring during off-design operation. To investigate the aerodynamic effect induced by morphing turbofan blades, a scaled test rig fan design is introduced. The low hub-to-tip ratio fan design is tailored for an increased deformability towards a piezoelectric actuation, while maintaining a sufficiently high aerodynamic on-design efficiency. The design measures considered include the rotor main dimensions, the blade profile design as well as 3D design features, such as sweep and dihedral. Since the adaptive fan design favours actuators that aim for an elevated blade cambering, corresponding actuation concepts are investigated in further detail. Considering a fan test rig set-up without core and a fixed nozzle, FEA morphing simulations are coupled with stationary 3D RANS passage CFD simulations and the detailed aerodynamic morphing effects are discussed. Finally, integral performance map effects are evaluated with respect to the stationary test rig working line, also taking into account the simplifications made during the morphing evaluation.