RANS-based Aerodynamic Shape Optimization of a Blended-Wing-Body Aircraft Zhoujie Lyu * Joaquim R. R. A. Martins † Department of Aerospace Engineering, University of Michigan, Ann Arbor, MI A series of RANS-based aerodynamic shape optimization for an 800-passenger blended-wing-body aircraft is performed. A gradient-based optimization algorithm and a parallel structured multiblock RANS solver with Spalart–Allmaras turbulence model are used. The derivatives are computed using a discrete adjoint method considering both frozen-turbulence and full-turbulence assumptions. A total of 274 shape and planform design variables are considered. The objective function is the drag coefficient at nominal cruise condition. Lift, trim and root bending moment are constrained. Control surfaces at the rear centerbody are used to trim the aircraft via a nested free-form deformation volume approach. The optimized design is trimmed and stable in both on- and off-design conditions. The drag coefficient of the optimized design is reduced by 37 counts with trim and bending moment constraints satisfied. The addition of planform design variables provide an additional 2 drag count reduction. I. Introduction Fuel burn has become the largest contributor to the direct operating cost of airlines due to the increasing price of fuel. The fuel cost per passenger-mile has more than doubled from 2001 to 2010 [1]. For this reason, current research in aircraft design is placing more emphasis on fuel burn reduction than ever before. One of the most promising studies to reduce fuel burn is the design of unconventional aircraft configurations. Unconventional aircraft configurations, such as the blended-wing-body (BWB) configuration, have the potential to significantly reduce emissions and noise of future aircraft. The BWB configuration is characterized by an airfoil-shaped centerbody that integrates payload, propulsion, and control surfaces. Compared to the classic wing-and-tube fuselage configuration, the BWB has superior aerodynamic performance [2, 3, 4]: the reduction in wetted area substantially reduces skin friction drag; the all-lifting design reduces wing loading and improves the spanwise lift distribution; the smooth blended wing-centerbody intersection reduces interference drag; and the area-ruled shape of the BWB reduces wave drag at high transonic speeds. The centerbody provides a substantial portion of total lift, thus reducing the wing-loading and resulting in a higher overall L/D. The low wing-loading allows the BWB to have excellent low-speed flight characteristics as well, making heavy high lift mechanisms, such as double-slotted flaps, redundant. The cross-sectional area of the BWB is similar to the Sears– Haack body, which results in lower wave drag at transonic speeds, according to Whitcomb’s area rule [5]. Despite various aerodynamic benefits, the aerodynamic shape of the BWB also brings challenges to the design process. The complex shape of the BWB may cause difficulty during manufacturing. Without the conventional empennage, the chordwise lift distribution on the centerbody needs to be carefully designed to maintain a positive static margin. The thick airfoil shape of the centerbody also makes it a challenge for the BWB to achieve low drag and generate sufficient lift at a reasonable deck angle. Several authors have previously investigated the aerodynamic shape optimization of the BWB configuration. Liebeck [6, 2] and Wakayama [7, 8] presented the multidisciplinary design optimization (MDO) of the Boeing BWB- 450 using a vortex-lattice aerodynamic solver. The trim and stability of the BWB have also been considered. Qin et al. [4, 9] performed a progressive aerodynamic optimization of the European MOB BWB geometry, including in- verse design and 3D shape optimization with a trim constraint. Peigin and Epstein [10] used a genetic algorithm and * PhD Candidate, Department of Aerospace Engineering, University of Michigan, AIAA Student Member † Associate Professor, Department of Aerospace Engineering, University of Michigan, AIAA Associate Fellow 1 Downloaded by UNIVERSITY OF MICHIGAN on April 1, 2014 | http://arc.aiaa.org | DOI: 10.2514/6.2013-2586 21st AIAA Computational Fluid Dynamics Conference June 24-27, 2013, San Diego, CA AIAA 2013-2586 Copyright © 2013 by Zhoujie Lyu and Joaquim R.R.A. Martins. Published by the American Institute of Aeronautics and Astronautics, Inc., with permission. Fluid Dynamics and Co-located Conferences