This work aims at proposing an aerodynamic design optimization methodology entirely based on Computer-Aided Design (CAD) representations, yielding a fully integrated geometry-simulation-optimization framework. Specifically, the geometry to optimize is defined thanks to CAD standards, like Non-Uniform Rational B-Splines (NURBS); the resolution of compressible Euler / Navier-Stokes equation is achieved using a Discontinuous Galerkin (DG) method based on rational Bézier elements with adaptive mesh refinement, which is geometrically exact with respect to CAD boundaries; The global optimization of CAD control points is carried out using a Bayesian Optimization method. The whole design chain is therefore consistent with respect to the CAD geometry. The proposed approach is demonstrated for the optimization of an airfoil in transonic regime.