The blended-wing-body represents a potential revolution in efficient aircraft design. A lift-constrained drag-minimization optimization problem is solved for the optimal shape of a blended-wing-body transonic regional jet. A Newton-Krylov solver for the Euler and Reynolds-Averaged Navier-Stokes (RANS) equations is coupled with a gradient-based optimizer, where gradients are calculated via the discrete adjoint method. A 98-passenger regional jet is optimized for a 500nmi mission at 40,000ft and Mach 0.8. A series of single and multipoint optimization problems using both the Euler and RANS equations are considered in order to examine the trade-offs between the imposition of different constraints including trim and longitudinal static stability. Drag reductions of up to 55% and 38% are achieved for the Euler and RANS-based optimizations respectively. In each case an elliptical lift distribution is attained on the wing, shocks are eliminated, and in the RANS-based optimization the large regions of highly separated flow on the baseline design are greatly reduced. These drag reductions are achieved while both trimming and stabilizing the baseline design.
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