Optimal inlet shape design of N2B hybrid wing body configuration

The N2B hybrid wing body aircraft was conceptually designed to meet environmental and performance goals for the N+2 generation transport set by the subsonic fixed wing project. 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 engine fan face and nozzle exhaust planes are provided by the NPSS thermodynamic engine cycle model. The flow simulations revealed challenging design issues arising from boundary layer ingestion offset inlet and airframe-propulsion integration. An adjoint-based optimal design was then conducted for the inlet shape to minimize the airframe drag force and flow distortion at fan faces. Design surfaces are parameterized by NURBS, and the cowl lip geometry is modified by a spring analogy approach. By the drag minimization design, flow separation on the cowl surfaces are almost removed, and shock wave strength got remarkably reduced. For the distortion minimization, a circumferential distortion indicator DPCP_avg was adopted as the design objective and diffuser bottom and side wall surfaces are perturbed for the design. The distortion minimization resulted in a 12.5 % reduction in the objective function.