Preface

Welcome to IST. For the third time we meet in Lisbon to exchange experiences and discuss views on CFD Uncertainty Analysis. It is encouraging that again a significant group of people concerned with the confidence in the reliability of their computational results is gathering. There are eight presentations, four from North America (three from the U.S.A. and one from Canada) and four from Europe. This means a substantial growth of the participation from North America, which is appreciated.

This 3^rd Lisbon Workshop is the last one in a series of three. In the first workshop (2004) we focused on verification, clearly distinguishing it from validation, but not fully recognizing the dual nature of verification, viz. code verification (error evaluation) and calculations verification (error estimation). So when the error bands estimated for the two test cases did not overlap, it was unclear whether the uncertainty estimation procedures were too optimistic or code implementation errors played a role.

Therefore, in the second workshop (2006) a Manufactured Solution was added as an obligatory test case. The test case of the first workshop, the flow over a backward facing step (included as test C-30 in the ERCOFTAC database) was retained. No common grids were provided; instead the participants were left free to select the grids to their own preference. Thus an impression of the effect of grid lay-out on the results was obtained. However, in evaluating the results we were forced to admit that nobody had succeeded to provide the “true” asymptotic solution of the backward-facing step problem. Can we do better?

Now (2008) we are in Lisbon to make the analysis complete and to go through all three stages: code verification, solution verification and validation. Thanks to early access to the work of the ASME PTC-61 Committee: Guide on Verfication and Validation in Computational Fluid Dynamics and Heat Transfer, a well-defined validation exercise could be added to the tasks to be carried out by the participants of this workshop.

We are very happy that Patrick Roache and Hugh Coleman, both with an outstanding reputation in the field of uncertainty analysis, are prepared to present an invited lecture and to lead the discussions during the workshop. We sincerely hope that, with their assistance, the workshop will lead to improved insight and to reliable procedures for CFD uncertainty analysis in practical engineering. Let us together try to put the cherry on top of the cake in Lisbon III.

The organisers