Shape design optimization of embedded engine inlets for N2B hybrid wing-body configuration

The N2B hybrid wing-body aircraft with embedded engines was conceptually designed to meet environmental and performance goals for the N+2 generation transport set by the Subsonic Fixed Wing project of NASA Fundamental Aeronautics Program. In the present study, flow simulations are conducted around the N2B configuration by a Reynolds-averaged Navier-Stokes flow solver using unstructured meshes. Boundary conditions at fan faces and engine exhaust planes are provided by the Numerical Propulsion System Simulation (NPSS) thermodynamic engine cycle model. The flow simulations reveal challenging design issues arising from the integration of boundary-layer-ingestion offset inlets with the wing-body airframe. Adjoint-based optimal designs of the inlet shape are then carried out to minimize the airframe drag force and flow distortion at fan faces. Design surfaces are parameterized by Non-Uniform Rational B-Spline (NURBS), and the cowl lip geometry is modified by a spring analogy approach. By the drag minimization design, a massive flow separation on the cowl surfaces is almost removed, and the strength of a shock wave unintended in the original design is now remarkably reduced. For the distortion minimization design, the diffuser bottom and side walls are reshaped to minimize flow distortion at fan faces. This minimization results in a 12.5% reduction in distortion.