Aerodynamic Redesign Using Discrete Adjoint Approach on Overset Mesh System

An adjoint-based design approach for the delicate treatment of complex geometry is presented by using an overset mesh technique. Overset blocks, such as collar and tipcap grids, which are commonly used in accurate drag prediction, are employed to evaluate the applicability of the proposed design approach to practical problems. Various pre- and postprocessing techniques for overset flow and sensitivity analyses are implemented to develop a robust gradient-based optimization method on an overset mesh topology. In preprocessing, overlap optimization, which can provide an accurate overset solution and enhance convergence characteristics, is adopted to automatically construct the block connectivity. A new postprocessing method, the spline-boundary intersecting grid scheme, is introduced by reflecting the ratio of the surface cell area for accurate prediction of aerodynamic coefficients and a convenient evaluation of sensitivities under a parallel computing environment. For the sensitivity analysis, the adjoint formulation for the overset boundary condition is implemented in the fully hand-differentiated sensitivity analysis code. A three-dimensional discrete adjoint solver on the overset mesh system is developed by exploiting the overset flow analysis techniques. Good convergence characteristics of the adjoint solver can be achieved by using the automatic construction process of block connectivity. The derivatives of aerodynamic coefficients can be obtained by an efficient and accurate postprocessing technique. The present overset adjoint formulation and flow analysis techniques are validated by comparing the flow and sensitivity analyses, as well as the design results, with those of a single-block case for a transonic wing. Finally, careful designs are carried out by minimizing the drag of a three-dimensional wing–body configuration. The design results successfully demonstrate the capability of the present design approach.The authors appreciate the financial support provided by the second stage of the Brain Korea 21 Project in 2007 for Mechanical and Aerospace Engineering Research at Seoul National University, and by the Smart Unmanned Aerial Vehicle Development Program of the 21st Frontier Research and Development Program sponsored by the Ministry of Commerce, Industry, and Energy