# wall function and 1st grid

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 February 18, 2017, 08:59 wall function and 1st grid #1 Member   bye bye my blue Join Date: Sep 2016 Posts: 37 Rep Power: 5 I'm using kEpsilon on 2d airfoil naca 0015 and boundary layer (0.03m). my questions. 1) yPlus (postprocess -func yPlus) I don't know meaning of min, max, average... 2) 1st grid To use wall function, 1st grid is 3010^6 on textbook. this results was 0.023m. So I'm using 0.03 on V.L. is it right?? Thanks a lot

 February 18, 2017, 13:02 #2 Senior Member     Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 590 Rep Power: 9 > I got boundary layer using B.L for re>10^6 on textbook. this results was 0.023m. So I'm using 0.03 on V.L. is it right?? The viscous boundary layer reaches to y+~30. Up to this wall distance the relation between y+ und u+ (and therewith between y und U_tangential) is more or less proportional. This is the reason for selecting y+=30 for the first mesh layer. If your textbook says, the boundary layer thickness is 1e-6 meters you need an first layer in the region of 3e-5 meters. y+ depends on the "free stram velocity". That is the turbulent velocity away from the wall, let's say y+>100. This value may change over your geometry, and therwith y+. The mesh has to take this into account. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)