Coupled Aeropropulsive Optimization of a Three-Dimensional Boundary-Layer Ingestion Propulsor Considering Inlet Distortion

Boundary-layer ingestion (BLI) promises increased aircraft efficiency, but excessive inlet distortion must be avoided to prevent fans that are too heavy or structurally infeasible. We propose a new approach to study the effect of distortion on BLI propulsors via an aeropropulsive design optimization with a constraint on inlet distortion using highly efficient gradient-based methods with analytic derivatives. The fully coupled aeropropulsive model includes a three-dimensional Reynolds-averaged Navier-Stokes aerodynamic analysis of the flow and a thermodynamic cycle model of the propulsor fan. We minimize the shaft power required at cruise for the aft BLI thruster by varying the propulsor size and the shape of the propulsor nacelle and aft fuselage. Optimizations are performed with and without the inlet distortion constraint for different aft-propulsor sizes to study the impact of the constraint on overall BLI performance. The results show that imposing a distortion constraint increased the required propulsor shaft power by up to 1.2% relative to the unconstrained case, and that smaller propulsors suffer lower performance degradation than larger ones. The results underline the importance of using a fully coupled aeropropulsive model to predict BLI performance and demonstrate the power of aeropropulsive optimization in the design of BLI configurations.