This paper presents an overview of the 3 Workshop on CFD Uncertainty Analysis, dedicated to Verification (of Code and Solution) and Validation, held in Lisbon in October 2008. The Workshop proposed three different exercises for incompressible Reynolds-averaged Navier-Stokes (RANS) flow solvers: Code Verification with a Manufactured Solution, resembling a near-wall turbulent flow; Solution Verification for the flow over a backward facing step; Validation with a simplified version of the procedure proposed by the ASME VV the grid density required to attain the “asymptotic range” in RANS solutions is significantly higher than what is used nowadays in calculations for engineering purposes; it is nearly impossible to recognize that a given solution is in the “asymptotic range” from a single evaluation of the observed order of accuracy. As a consequence, in many practical RANS solutions it is safer to assume that the data are not in the “asymptotic range” (instead of blaming the uncertainty estimator for being too conservative). The Validation procedure tested in the Workshop is clearly a step forward compared to the “standard” graphical comparison between experiments and numerical predictions.

This paper presents an overview of a Workshop dedicated to the Verification of Calculations held in Lisbon in October 2004. The Workshop aimed at evaluation of Computational Fluid Dynamics Uncertainty Estimators by comparing results of six groups on two twodimensional incompressible turbulent flows involving separated turbulent flows. Various numerical methods were represented, and calculations were done on smooth grids as well as deliberately poor grids in order to burden the Uncertainty Estimators. Even though local grid convergence was often non-monotone, the overall consensus evaluation was generally favorable for the Grid Convergence Index and the Least Squares version of it, as well as a monogrid Error Transport Equation method. Some residual doubts remain on the inter-group comparisons because of conceptual modelling differences and the possibility of undetected coding errors. These could be eliminated by the use of a realistic exact analytical solution produced by the Method of Manufactured Solutions, and the consensus favored this approach for a second Workshop on this theme.