# criteria for result validation

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 December 4, 2001, 09:21 criteria for result validation #1 Matthias Guest   Posts: n/a Sponsored Links which criteria are the most important to define a simulation good or bad? IŽam working with cfdesign which is an add-on for MSC-Nastran and i simulate the flowforces in a hydraulic valve. The flow is turbulent with a pressuredrop of 70e+05 Pa and i use the K-eps turb. model. There are effects i donŽt understand: - when a simulation is completed a take a look on the residualŽs of pressure and velocity, if they are small <0,001 iŽam defining the solution for convergent and the mesh for adequate. - the second data i observe are the "y plus-values" on the walls of interest for the flowforces (shearstress*Area + pressure*Area) => now my problem is that i get only results that match with experimental results if the mesh is very fine, but the finer the mesh the smaller the y-plus values. The y-plus values should be in a range of 35 < y+ < 350; if they are to small the wallnear nodes are to close to the wall and do not represent the physic. => which criteria are most important for validating a result ? => are the y-plus values less important ? => ... mfg Matthias =>

 December 6, 2001, 14:55 Re: criteria for result validation #2 chidu Guest   Posts: n/a Hi Matthias, Is it possible for you to refine your mesh everywhere except near the wall? As such, it is a clear requirement for the use of wall-functions that the first y+ should be between the range you have specified. On the other hand, if you have the required resources to capture the sub-layer, why don't you use a low Re model right down to the wall?? chidu...

 December 6, 2001, 16:14 Re: criteria for result validation #3 Joern Beilke Guest   Posts: n/a The convergency it no measurement of the correctness of the solution. If your mesh is too coarse then even a converged solution might be completly wrong.

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