Aerodynamic Shape Optimization of a Truss-Braced-Wing Aircraft Davide Ivaldi, ∗ Ney R. Secco, † Song Chen, ‡ John T. Hwang, § Joaquim R. R. A. Martins ¶ University of Michigan, Ann Arbor, Michigan, United States The truss-braced wing is an aircraft configuration that has the potential to be more efficient than conventional configurations. The coupling between aerodynamics, structures, and propulsion that is present in this configuration significantly increases the complexity of the design, but it offers the potential for a large improvement in performance over the cantilever wing, which we aim to achieve through numerical optimization in this study. Previous studies have primarily used low-fidelity tools that rely on empirical equations or low-order models. Here, we perform high-fidelity aerodynamic shape optimization using the RANS equations with 750 shape and twist design variables. Through optimization, we are able to reduce the drag by more than 28% compared to the baseline geometry, obtaining a final L/D ratio of 25.3, which is a lower than expected value due to high interference drag caused by limited shape design flexibility in the junctions. Despite the limitations, we believe that these results can provide a useful benchmark for future studies involving the truss-braced wing configuration, in addition to revealing insights regarding the complex aerodynamic phenomena asso- ciated with this configuration. I. Introduction The rapid progress of air travel in the 20th century was an important development that had a positive impact on society. Airliners provide efficient, fast, and safe transportation unmatched by any other means of long distance travel. However, a continuous evolution is required for aircraft to maintain the current trends and avoid threats to air transportation over the coming decades, such as rising fuel costs. Also, due to the growing number of aircraft operating on a daily basis, the optimization of transonic aircraft is becoming more and more important. Even a minor improvement that leads to a small decrease in drag coefficient or aircraft weight can have large benefits in the long run. Indeed, during the last few decades, more and more attention has been paid to reduce aircraft fuel consumption and emissions, and this trend is expected to continue in the years to come. Over the last 50 years, transonic commercial aircraft have converged upon what appear to be two common solu- tions: low cantilever wing with either under-wing or fuselage-mounted engines. Clearly, there are some differences that characterize the various aircraft, but it is unlikely that large strides in performance will be possible without a significant change of vehicle configuration. Among all the different, innovative configurations which were suggested in the last 20 years, the truss-braced wing seems to be particularly interesting. In a general sense, the truss-braced configuration adds two structural members to the wing. The first one, which is called main strut, is designed to carry primarily axial loads and joins one point on the wing to a point on the fuselage. The second one, which is called jury strut or vertical strut, connects the main strut and the wing. The concept of the truss-braced-wing configuration dates back to the early 1950s, and it was proposed again by NASA at the beginning of the century as one of the N+3 (2030- 2035) generation aircraft concepts. It has been proved that the truss-braced-wing configuration is able to achieve larger reductions in fuel consumption than other unconventional configurations [1, 2]. Aircraft designers have always tried to use high-aspect-ratio wings in order to reduce the lift-induced components of drag. However, many practical issues arise as slender wings can suffer from higher bending and torsional stresses than shorter ones. The coupling of these two modes can also lead to severe consequences, such as the triggering of ∗ Visiting Scholar, Department of Aerospace Engineering † Ph.D. Candidate, Department of Aerospace Engineering ‡ Visiting Scholar, Department of Aerospace Engineering § Postdoctoral Research Fellow, Department of Aerospace Engineering ¶ Associate Professor, Department of Aerospace Engineering 1 Downloaded by University of Michigan - Duderstadt Center on December 14, 2017 | http://arc.aiaa.org | DOI: 10.2514/6.2015-3436 16th AIAA/ISSMO Multidisciplinary Analysis and Optimization Conference 22-26 June 2015, Dallas, TX 10.2514/6.2015-3436 Copyright © 2015 by the American Institute of Aeronautics and Astronautics, Inc. All rights reserved. AIAA AVIATION Forum