Three-dimensional contour bumps for transonic wing drag reduction

Abstract

Two-dimensional and three-dimensional contour bumps are designed and optimized for substantial wave drag reduction for an un-swept natural laminar flow (NLF) wing (RAE5243 aerofoil section) at transonic speeds. An NLF aerofoil wing is chosen in this study, as shock control is more crucial for such wings due to the requirement of favourable pressure gradients on a substantial part of the wing. For the validation purpose and to focus on the wave drag issues, the boundary layer is assumed to be fully turbulent from the leading edge. Key bump geometrical parameters including the maximum height, the length, and the crest position have been chosen for the parameterization of the two-dimensional and three-dimensional shock control bumps. For the three-dimensional bumps, an array of the contour bumps is installed spanwise on the transonic wing and their width and spanwise spacing are chosen as additional design parameters. Both the two-dimensional and the three-dimensional bump shapes are optimized using a discrete adjoint-based optimization method. The performance of the three-dimensional contour bumps are compared in detail with the similarly optimized two-dimensional bumps both at and around the design point. The results show that, for the NLF wing studied, the optimized three-dimensional bumps are as effective as the optimized two-dimensional bump in terms of total drag reduction at the given design point, despite the significant difference in their geometrical shapes. More importantly, in terms of the operational range for varying lift conditions for practical applications, the three-dimensional bumps outperform the two-dimensional bump by a substantial margin.