Testing Uncertainty Estimation and Validation Procedures in the Flow Around a Backward Facing Step

This paper presents an evaluation of a method for the estimation of the discretization uncertainty based on a Least Squares version of the Grid Convergence Index and a recently proposed Validation procedure in the calculation of the two-dimensional flow of an incompressible fluid over a backward facing step. Solution Verification studies are performed for three grid sets with the finite-difference and finite-volume versions of PARNASSOS using the one-equation turbulence model of Spalart & Allmaras model and the baseline and shear-stress transport variants of the k−ω two-equation turbu-lence models, proposed by Menter. The results show that it is difficult to obtain reliable estimates of the uncertainty of flow quantities in turbulent flows. With a procedure based on the determination of the observed order of accuracy, the level of grid refinement and/or solution accuracy required to obtain reliable estimates of the numerical uncertainty is much finer than what is commonly used nowadays. The proposed procedure for Validation is clearly more reliable than the popular graphical comparison of predictions and experiments.