Comparison between Gradient-free and Adjoint Based Aerodynamic Optimization of a Flying Wing Transport Aircraft in the Preliminary Design.

Abstract

This paper describes investigations of planform and shape optimizations for a flying wing transport aircraft with an Euler continuous adjoint method. For a prescribed lift the cost function will be the drag, which has to be minimized and implies a maximization of L/D. The results presented for the gradient based method using an adjoint solver are compared to an optimization performed with a gradient free approach. The different workflows and procedures will demonstrate the advantages and disadvantages of each particular optimization approach. The optimization procedure uses a freeform deformation technique for the design parameterization of the shape as well as for the surface mesh deformation required to determine the gradients. This combination of both tasks into one tool is advantageous because performing finite differences for evaluating the mesh sensitivities can be carried out with a constant grid topology. An example design case is also shown for demonstration purposes