Design Optimization of Rear-Fuselage Boundary-Layer Ingestion Shrouded Propulsor

The mitigation of the environmental impact of civil aviation is driving the development of new technologies with the potential for lower emissions, such as boundary-layer ingestion (BLI) configurations. BLI propulsion operates on the wake-filling principle, by energizing the low-momentum boundary layer developed past the airframe to reduce the kinetic energy waste that is needed in the jet of isolated propulsors to produce thrust. In this paper, we present a design optimization study of an aft-fuselage BLI propulsor using Reynolds-averaged Navier-Stokes simulations. The problem is formulated as a multi-objective optimization to maximize the ratio between net-force power and fan flow power in conjunction with the net force acting on the fuselage. A design space exploration is first conducted for an axisymmetric parametric model, revealing the primary influence of global size variables. An optimized two-dimensional model is then used to generate an upswept three-dimensional fuselage and propulsor geometry, whose nonaxisymmetric nacelle external cowl is further optimized to improve the uniformity of the Mach number and the mass flux distribution along the azimuth. The final design exhibits a fan pressure ratio of 1.31 and the ratio between the rear-fuselage thrust power to fan flow power is 0.79, 3% higher than the initial nonoptimized axisymmetric geometry in absolute terms.