# Continuity Residual high but total mass convergence achieved?

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 February 8, 2016, 06:21 Continuity Residual high but total mass convergence achieved? #1 New Member   Join Date: Feb 2016 Posts: 2 Rep Power: 0 Hi everyone, I'm working on designing an aerodynamics package for a Formula Student team and am relatively new to CFD. One thing that has been bothering me is a high continuity residual I am getting for my simulations. My x,y,z-velocity residuals are all around 1e-5, and my k and omega residuals steady around 1e-3. However, my scaled continuity residuals stays around 1e-2. Despite this, my mass flow rate between my inlet and outlet only differs by 0.0005% (all other BCs are moving walls). I know that residuals are ideally meant to drop 3 orders of magnitude at least for convergence but Fluent's scale factor for the cont. equation depends on the first 5 iterations. Would this high continuity residual be justified given the total mass of the wind tunnel has converged? My BCs are: Inlet (15m/s) Pressure Outlet Symmetry Plane Roof (moving wall -> 15m/s) Wall (moving wall -> 15m/s) Ground (moving wall -> 15m/s)

 February 8, 2016, 10:24 Under-Relaxation factor #2 New Member   InduSekhar Roy Join Date: Feb 2016 Posts: 2 Rep Power: 0 You can try decreasing the Under-Relaxation factor. Setup-> Solution Controls -> Try decreasing the "Under-Relaxation factor" for "momentum" from 0.7 to 0.6. You can try decreasing till 0.1, even 0.01. But, it is advised not decrease it below 0.1 to get accurate result. http://www.cfd-online.com/Forums/flu...nvergence.html http://www.cfd-online.com/Forums/flu...nvergence.html I hope this helps.

 Tags continuity, mass, residual, residuals