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josip76 May 26, 2011 20:08

fluent convergence problem

Im looking at solving a supercritical airfoil case at M=0.73 and Re=6.5E6 I meshed the airfoil in ICEM and am using fluent as my solver. My problem is that the case does not convege in fluent. Im using a C-grid topology and have built both both single- and 2-block grids (the more refined boundary layer region in the 2-block grid gave no improvement in results if fact the results seemed to get worse). My off wall spacing was calculated at y+=1 (any larger off wall spacing and oscillations appear in the pressure plot) and a spacing expansion ratio of 1.05. Fluent does worn me of a high aspect ratio in the mesh near the wall. Adding more nodes along the airfoil does not seem to help at all and any larger spacing again yields poor resolution of the pressure around the airfoil. When I solve the case in fluent using the pressure based solver the solution converges but is incorrect. When i solve it using the density based solver the equation residuals converge very quickly to 1.2e-2 but then begin to oscillate (by this point in time the force monitors have not converged in fact they seem to divergence). I have looked at the quality of the mesh and the amount of skew present and have improved the mesh with regard to both of them (though these improvements seemed to have little effect on the solution).I was wondering if you knew what the cause of this behaviour could be. Additionally, i found that smoothing my mesh in ICEM yielded it unreadable by fluent (fluent gave an error and froze) does this mean the blocking in the mesh is badly layed out?

Thanks for all help

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