The application of composite fans enables disruptive design possibilities but increases sensitivity to multi-physical resonance between aerodynamic, structure dynamic and acoustic phenomena. As a result, aeroelastic problems increasingly set the stability limit. Test cases of representative geometries without industrial restrictions are a key element of an open scientific culture but are currently non-existent in the turbomachinery community. In order to provide a multi-physical validation benchmark representative of near-future UHBR fan concepts, the open-test-case fan stage ECL5 was developed at Ecole Centrale de Lyon. The design intention was to develop a geometry with high efficiency and a wide stability range that can be realized using carbon fibre composites. This publication aims to introduce the final test case, which is currently fabricated and will be experimentally tested. The fan blades are composed of a laminate made of unidirectional carbon fibres and epoxy composite plies. Their structural properties and the ply orientations are presented. To characterize the test case, details are given on the aerodynamic design of the whole stage, structure dynamics of the fan and aeroelastic stability of the fan. These are obtained with a state-of-art industrial design process: static and modal FEM, RANS and LRANS simulations. Aerodynamic analysis focuses on performance and shows critical flow structures such as tip leakage flow, radial flow migration and flow separations. Mechanical modes of the fan are described and discussed in the context of aeroelastic interactions. Their frequency distribution is validated in terms of resonance risk with respect to synchronous vibration. The aeroelastic stability of the fan is evaluated at representative operating points with a systematic approach. Potential instabilities are observed far from the operating line and do not compromise experimental campaigns.

Ultra High Bypass Ratio (UHBR) fan is a promising solution for the next decades to improve the turbofans efficiency and to reduce the environmental impact of the aeronautical propulsion. The high aspect ratio and the use of composite material for these fan blade induce new coupling problematics between aerodynamic, aeroelastic and aeroacoustic phenomena. In this context, a new open-test-case fan stage ECL5 is provided to the turbomachinery community within the European CleanSky-2 project CATANA. In Part-1 of this publication, the test case is introduced with details on geometry, methodology and aerodynamic design of the whole stage, whereas Part-2 focuses on structure dynamics and aeromechanical stability. This paper aims to provide the mechanical and aeroelastic stability characteristics of the fan stage obtained with a state-of-art industrial design process. These analyses enable to ensure the integrity for the anticipated experimental campaigns. The fan blades are fabricated of unidirectional carbon fibres and epoxy composite layers. Fibre orientations of each layer are parameters which enable to modify the mechanical behaviour with minimal impact on the aerodynamic performance. Details on the structural properties, the manufacturing process and the layer orientations will be presented. Mechanical analysis of the fan, determined by finite element method, is provided. The specific methodology to account for the anisotropy of the blade composite structure is introduced. The static deformation along the working line and first mechanical modes of the fan are described and discussed in the context of aeroelastic interactions. To be representative of industrial configurations and to enable complete experimental campaigns, it is necessary that the fan presents stable operating conditions at every planned experimental rotation speed. Its aeroelastic stability is investigated on the 3D isolated blade with time-linearized method. This method provides similar results to unsteady simulations but with lower computational cost in the absence of circumferentially convected aerodynamic disturbances occurring near stall. Thus, the aeroelastic stability is characterised across the complete operating range for the first three blade eigenmodes.