A multidisciplinary optimization method for designing boundary layer ingesting inlets

The Blended-Wing-Body is a conceptual aircraft design with rear-mounted, over-wing engines. Two types of engine installations have been considered for this aircraft. One installation is quite conventional with podded engines mounted on pylons. The other installation has partially buried engines with boundary layer ingesting inlets. Although ingesting the low-momentum flow in a boundary layer can improve propulsive efficiency, poor inlet performance can offset and even overwhelm this potential advantage. For both designs, the tight coupling between the aircraft aerodynamics and the propulsion system poses a difficult design integration problem. This dissertation presents a design method that solves the problem using multidisciplinary optimization. A Navier-Stokes flow solver, an engine analysis method, and a nonlinear optimizer are combined into a design tool that correctly addresses the tight coupling of the problem. The method is first applied to a model 2D problem to expedite development and thoroughly test the scheme. The low computational cost of the 2D method allows for several inlet installations to be optimized and analyzed. The method is then upgraded by using a validated 3D Navier-Stokes solver. The two candidate engine installations are analyzed and optimized using this inlet design method. The method is shown to be quite effective at integrating the propulsion and aerodynamic systems of the Blend-Wing-Body for both engine installations by improving overall performance and satisfying any specified design constraints. By comparing the two optimized designs, the potential advantages of ingesting boundary layer flow for this aircraft are demonstrated.