Multi-operating-point adjoint aerodynamic optimization of the fan of a high bypass-ratio engine

A multi-operating-point adjoint aerodynamic optimization of the fan of a high bypass-ratio aero-engine is presented in this paper. Flow solutions at both design and off-design operating points are firstly obtained using an in-house Newton— Krylov flow solver, and compared with a commercial solver to verify their accuracy. Subsequently, an automatic gradientbased optimization workflow is established to perform multi-operating-point adjoint aerodynamic optimization. Three typical operating points related with the bypass performance, i.e. design, bypass near stall and bypass near choke points are considered in order to achieve bypass performance improvement at the design point while retaining stall margin of bypass at the same time. 225 parameters are chosen as optimization variables for the current optimization. A discrete adjoint solver is used to obtain gradients efficiently and accurately at the design point and near choke/stall points. The optimization results show that the efficiency of the bypass at the design point is increased by about 0.6% within just 19 optimization steps, while all constraints are satisfied. This demonstrates that the Newton—Krylov flow and adjoint solvers are efficient and robust tools for performing automatic multi-operating-point optimization of fans of high bypass-ratio engines to increase design point efficiency and retain stall margin simultaneously.