Browsing by Author "Vavalle, Armando"

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    Response surface aerodynamic optimisation for blended wing body aircraft
    (Cranfield University, 2005-02-08) Vavalle, Armando; Qin, N.
    This study is concerned with a methodology for the aerodynamic analysis and preliminary design of a novel configuration for high subsonic civil transport, based on the flying wing concept, known a Blended Wing Body (BWB). A response surface based optimisation method is developed, enabling the designer to monitor the effect of shape modification on the controllability of the aircraft in both longitudinal and lateral/directional motion and on the Wing structural weight, while maximising the aerodynamic efficiency. The design aspects considered included high- speed aerodynamics, flight static-stability and trim characteristics. The response surface Scheme employs a space filling design of experiment technique to build least square fitting quadratic polynomials, used in place of the original computational modules in a gradient based search. A optimisation test indicated that the present method is more effective in leading the design near to the global optimum as opposed to a conventional gradient method with direct search, despite that the constructed approximation may not represent accurately the actual surface. With this system, multiple constrained optimisation problems are successfully solved in the favourable case of smooth objective/constraint function. Where these functions may exhibit high non-linear trends, an iterative response surface method refining both approximation and bounds of the design space is proposed. The capabilities of such a technique are shown for transonic aerofoil optimisation problems, demonstrating that the proposed method is more efficient and more effective than some other state-of- the-art methods. As a result of these studies, the aerodynamic efficiency of a large capacity BWB configuration has been considerably improved by re-designing the external shape to generate a spanwise loading intermediate between triangular and elliptic. The longitudinal static stability analysis revealed that the aircraft is stable except at low- weights with zero-payload. The lateral/directional analyses showed that the aircraft is stable in roll, but unstable in yaw. Despite that the winglets are found to stabilise the aircraft, it is directionally unstable without additional vertical stabilisers. I