Optimising blade profiles to extend the operating range in BLI fan application

Boundary Layer Ingestion propulsors operate in an adverse aerodynamic environment with high levels of distortion. With the purpose of extending the operating range of transonic fan rotors for BLI applications, in this paper we present an optimisation study focused on blade profiles design under different working conditions. Quasi-2D blade sections are optimised using a genetic algorithm and numerical simulations, by varying the camberline and thickness distribution. A method to efficiently achieved a combination of total pressure ratio at a given relative inlet Mach number is devised. The isentropic efficiency is optimised at the design point, concurrently with the stall total pressure ratio at a lower inlet Mach number, in a multi-objective fashion. The results obtained for two transonic inflow conditions are used in a successive three-dimensional refinement study. Optimised profiles are utilised in the upper span of a 3D fan rotor working under a BLI distorted inlet flow. Blade chord and stagger angles in the upper half of the span are optimised using a Bayesian approach with an axisymmetric inflow profile obtained by circumferentially averaging the full-annulus field. The comparison of the characteristic maps of two Pareto optimal individuals from the 3D optimisation with an initial reference rotor show that the optimisation improved the peak efficiency and the near stall behaviour.