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Andres Bernal Ortiz January 9, 2007 23:54

Model Validation
Hi, I'm working in airfoil analisys (NACA4415 and 4418) to be used as part of a UAV wing. For validation purposes I need to prove my model with Re data as showed in the NACA REPORTS, i selected Alfa=4 dgrees and Re=3e6...In the technical aspects of the report I foun that the cord used was 2ft but I cant find anything about the Rho and Viscosity value they've used.

I selected ISA conditions (T 15 C - Rho 1.225 Kg/m3 - Viscosity 1.7986e-5 Kg m^-1 s^-1 - Sea Level)...but the Cl and Cd doesn't match reality..

The analisys data are: - Turbulence model = SST medium turbulence 5% - Y+ obtained 2.8 - Airfoil with wall no slip bound. cond. - Inlet with Cart. velocity as bound. cond. - Outlet with Static Press. 0 atm as bound.cond - High Resolution - Conservative - AutoTimescale - MAX with 1e-4

I'm kind of worried because i work really hard but more that i work, more the results diverge from NACA DATA.

Joe January 10, 2007 08:36

Re: Model Validation
Grid independance?

Andres Bernal Ortiz January 10, 2007 10:55

Re: Model Validation
Thanks for taking the time for answer Joe..If I double the mesh (leaving the same spacing but increasing the number of nodes) the Cl and Cd values must be the same as the original mesh (obtained after a trial and error process)?



Andres Bernal Ortiz January 10, 2007 11:30

Re: Model Validation
When I try to increase the number of nodes (im uisng ICEM)...the solver shows an error saying that there's a negative volume and that these analisys canno't be run..

Any ideas?


Joe January 10, 2007 11:41

Re: Model Validation
Deal with the icem problem and do a mesh independance study. Never claim a CFD result isnt duplicating reality before doing a MIS.

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