Aerodynamic Shape Optimization using Discrete Adjoint Formulation based on Overset Mesh Technique

Abstract

A new design approach for a delicate treatment of complex geometries such as wing/body configuration is arranged using overset mesh technique under large scale computing environment. For the in-depth study of the flow physics and highly accurate design, several special overlapped structured blocks such as collar grid, tip-cap grid, and etc. which are commonly used in refined drag prediction are adopted to consider the applicability of the design code to practical problems. Various pre- and post-processing techniques for overset flow analysis and sensitivity analysis are devised or implemented to adapt overset mesh technique to the design optimization problem based on Gradient Based Optimization Method (GBOM). In the pre-processing, the convergence characteristics of the flow solver and sensitivity analysis are improved by overlap optimization method. Moreover, a new post-processing method, Spline-Boundary Intersecting Grid (S-BIG) scheme, is proposed by considering the ratio of cell area for more refined prediction of aerodynamic coefficients and convenient evaluation of sensitivities under parallel computing environment. For the sensitivity analysis, adjoint formulations for overset boundary conditions are implemented into the existing fully hand-differentiated sensitivity analysis code. A smooth geometric modification on the overlapped surface boundaries and evaluation of analytic grid sensitivities can be performed by Spline patch and mapping from physical grids to the patched Spline function. Careful design works for the drag minimization problem of DLR-F4 are performed using the newly-developed and -applied techniques. And the design results from conventional design problem demonstrate the capability of the present design approach successfully.