Assessment of numerical uncertainty for the calculations of turbulent flow over a backward‐facing step

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Abstract
Numerical uncertainty analysis has been performed for the turbulent flow past a backward‐facing step. The analysis is based on calculations on seven non‐rectangular, but structured, grid sets that were provided by the organizers of the 2004 Lisbon Workshop (Proceedings of the Workshop on CFD Uncertainty Analysis, Lisbon, 21–22 October 2004). The calculations were performed by using a commercial code, namely, FLUENT with the Spalart–Allmaras one‐equation turbulence model. The present study constitutes a calculation verification process: a set of partial differential equations are solved on gradually refined grid sets, the selected quantities are extrapolated, and then the overall numerical uncertainty in selected quantities is estimated by various methods. Some new ideas are presented for estimating the coefficient of variation, which is related to standard deviation (or standard error of estimate in case of the least squares method).The major problem that stands out in extrapolation is the cases of non‐monotonic convergence. For such cases some alternative methods are proposed, and the results are compared to assess these methods. Copyright © 2005 John Wiley & Sons, Ltd.

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