# Reverse flow starting when about to converge

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 May 23, 2012, 16:56 Reverse flow starting when about to converge #1 Senior Member   Ananthakrishnan.A.S Join Date: Feb 2012 Location: Mumbai (Bombay), India Posts: 157 Rep Power: 10 I have a 3D wing which i need to analyse for lift and drag. Mach = 0.18 or V=58m/sec. ICEM CFD determinant 3*3*3 quality of mesh is 0.8 to 1. Wing span = 0.5715m mean aero chord = 0.13m Operating conditions are Model-SA air-constant density upper, lower and front face of far fields are velocity inlet in positive x direction, with turbulence = 1% and length scale of 0.015m Back surface of far field is pressure outlet..everything is at 1atm Solution method is at SIMPLE scheme and default options Initialization done from the inlet values. The calculation proceeds smoothly until 1000 iterations. It almost starts to converge but suddenly reverse flow starts and urbulent viscosity limited to viscosity ratio of 1.000000e+05 is also displayed..they keep increasing I have no clue about the reason!!!!...Pls help..

 May 23, 2012, 23:25 #2 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,420 Blog Entries: 6 Rep Power: 46 what are dimensions of domain extend ? I mean X, -X, Y, -Y and Z, -Z

 May 24, 2012, 02:39 #3 Senior Member   Ananthakrishnan.A.S Join Date: Feb 2012 Location: Mumbai (Bombay), India Posts: 157 Rep Power: 10 X is -1.1916m to 2.6183m Y is -1.27 to 1.27m Z is 0 to 0.991m @Far, the wing is the same one which i had posted earlier http://www.cfd-online.com/Forums/ans...-required.html

 May 24, 2012, 02:53 #4 Super Moderator   Sijal Join Date: Mar 2009 Location: Islamabad Posts: 4,420 Blog Entries: 6 Rep Power: 46 I would like to know these dimensions as chord (or any appropriate characteristic length) * X etc.

 May 24, 2012, 03:36 #5 Senior Member   Ananthakrishnan.A.S Join Date: Feb 2012 Location: Mumbai (Bombay), India Posts: 157 Rep Power: 10 i think you wanted to know if these values are calculated based on some characteristic length?? If so, yes..the far field was created as a multiple of chord length (5) The back surface of the far field is 20times (100) from the leading edge corner. The upper lower and front faces are 10 times (50) from the leading edge corner. Just now i had changed the bunching in the vertical dir near the wing to have good Y+. I increased it by two decimal points. The reverse flow stopped but turbulent viscosity ratio problem is still there. It came after 2000 iterations..I have no idea if there is a relation between them. Last edited by Ananthakrishnan; May 24, 2012 at 04:00.

 Tags convergence, divergence, reverse flow, turbulent viscosity

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