Optimal aero-structural design of an adaptive surface for boundary layer motivation using an auxetic lattice skin

The aero-structural design of an adaptive vortex generator for repeatable, elastic, deployment and retraction from an aerodynamically clean surface is presented. A multidisciplinary objective function, containing geometrically nonlinear finite element analysis and large eddy simulation, is used to derive the optimal adaptive geometry for increasing the momentum of the near-wall fluid. It is found that the rapid increase of in-plane membrane stress with deflection is a significant limitation on achievable deformation of a continuous skin with uniform section. Use of a 2D auxetic lattice structure in place of the continuous skin allows for significantly larger deformations and thus a significant improvement in performance. The optimal deformed geometry is replicated statically and the effect on the boundary layer is validated in a wind tunnel experiment. The lattice structure is then manufactured and actuated. The deformed geometry is shown to compare well with the FEA predictions. The surface is re-examined post actuation and shown to return to the initial position, demonstrating the deformation is elastic and hence repeatable.