Output-based error estimation and adaptive mesh refinement using viscous adjoint method

An adjoint-based error estimation and grid adaptation study is conducted for three-dimensional viscous flows with unstructured hybrid meshes. The error in an integral output functional of interest is estimated by a dot product of the residual vector and adjoint variable vector. Regions to be adapted are selected based on the local error of each node. The adaptive regions are refined by the newest-vertex bisection refinement algorithm and subsequent hybrid mesh refinement strategies. The present procedure is applied to a three-dimensional transonic viscous flow around the ONERA M6 wing. The same level of prediction accuracy for drag is achieved with much less mesh points than uniformly refined fine meshes. It is found that residual smoothing strategy which was very effective for inviscid flow cases does not improve the accuracy of error estimation.