Aerodynamic Design Optimization of a Flying V Aircraft

Abstract

Lately, commercial aviation has been moving towards the reduction of environmental impact and direct operating costs, due to the rapid increase in aircraft demand and air traffic congestion predicted for the next years. Several researchers have been abandoning the fully exploited conventional configuration and exploring novel arrangements, such as flying wings and blended wing bodies. The Flying V concept, proposed at TU Berlin in collaboration with Airbus GmbH, represents the focus of this research project, since the preliminary analyses have estimated remarkable aerodynamic benefits and weight savings. It is a V-shape flying wing with two cylindrical pressurised cabins placed in the wing leading edge and engines over the trailing edge; elevons provide longitudinal control and vertical tails double as winglets. The primary research goal is the aerodynamic design of the Flying V aircraft to assess whether this concept has better aerodynamic performances than the reference conventional configuration during cruise. The design philosophy selected for this project consists of a multi-fidelity design space exploration followed by two different design paths: dual step optimization, where planform and airfoil variables are subsequently varied, and single step optimization. Athena Vortex Lattice is used to rapidly investigate the feasible design space, whereas the Stanford University Unstructured code in the Euler mode is adopted for an accurate wave and vortex-induced drag estimation. The profile drag is computed by a separate empirical module. The three-dimensional geometry is automatically generated within the ParaPy framework (a Knowledge Based Engineering environment) according to a multi-level parametrization: the wing planform shape is parametrized with 10 variables, the profiles with 43 parameters, and the winglets are defined by 3 additional variables. Subsequently, the unstructured volume grid is produced by the Salome platform wrapped in ParaPy and then fed into the aerodynamic solver. The aerodynamic design is performed at one single cruise condition: the Mach number is equal to 0.85, the lift coefficient to 0.26, and the altitude to 13,000 m. The baseline configuration is progressively improved: the wave and vortex induced drag components are reduced, the wetted area is slightly decreased and the pitching moment coefficient about the reference centre of gravity location is almost null. The maximum lift to drag ratio of the single step optimized configuration is 23.7 at the cruise point: this value confirms the estimation of 25 of the conceptual phase. A 12% reduction in subsonic drag is achieved, with the desired pitching moment. The Flying V is then compared to the NASA Common Research Model, a conventional configuration benchmark, by using the same solver and a similar mesh refinement. The maximum lift to drag ratio of the NASA Common Research Model is 18.9, hence the Flying V is 25% aerodynamically more efficient at the design cruise condition.