Some Experiences About the RANS Modeling of UHBR Fan: The Case of ECL5/CATANA

With the advancement of modern fan architectures, dedicated experimental benchmarks are becoming fundamental to improve the knowledge of flow physics, to validate novel CFD methods, and to fine-tune existing methods for this kind of applications. In such a context, the open-test-case ECL5/CATANA provides a great opportunity for the aerodynamic and aeromechanic research community. The carbon fibre fan open-test-case, representative of a modern Ultra High Bypass Ratio (UHBR) architecture,has been designed and experimentally investigated at the Ecole Centrale de Lyon on a novel test facility with multi-physical instrumentation, providing a large database of high quality aerodynamic and aeromechanic measurements. In this paper, a thorough numerical study of the fan stage aerodynamics has been carried out using the URANS TRAF code developed at the University of Florence. The fan stage performance has been studied at design speed over the entire operating range. Results have been discussed and compared with numerical datasets provided by ECL. A detailed sensitivity on numerical schemes and state-of-the-art turbulence/ transition models allowed the selection of the best numerical setup to face UHBR fan simulations. Moreover, to have a deeper understanding of the fan stall margin, unsteady full-annulus simulations have also been carried out. The results showed the appearance of a blade tip instability, precursor of a rotating stall condition, that may generate non-synchronous blade vibration due to frequency matching with one of the fan natural frequencies.