Adjoint Based Aerodynamic Optimisation of a UCAV

An optimisation study for the 1303 UCAV has been co nducted attempting to minimise drag in the cruise configuration subject to constra ints designed to avoid flow separation at take"off. The methodology has been developed for pr oducing credible designs for this class of wing early in the design process and hence minim ising assumptions made during aircraft preliminary design. The design is achieved iterativ ely using a gradient based SQP optimiser where the objective is calculated using an in house multiblock CFD code MERLIN in Euler mode. The objective gradients are efficiently calcu lated using an in house discrete adjoint code adj"MERLIN. The high lift constraint is based on a quasi"vortex"lattice method with empirical relationships which place limits on the ‘ attainable’ leading edge thrust aiming to avoid flow separation. The resulting designs are an alysed using MERLIN in RANS mode with the k"ω turbulence model which shows that desi gns can be obtained with similar cruise drag to the original planar wing but with considera bly improved high lift performance.