# reversed flow

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 April 17, 2007, 08:32 reversed flow #1 mvee Guest   Posts: n/a hi during solution i found reversed flow in some faces still my program runs and residual for continuity is of the order 1e-2. so can it be harmful or misleading the solution? how can it be cured? thanks in advance

 April 17, 2007, 09:19 Re: reversed flow #2 Gernot Guest   Posts: n/a Try to avoid backflow in areas you want to know the flowsolution. If the in/outlets that causes this backflow are far enough away then donīt worry. If they are not than enlarge the calculation area. P.s.: Sometimes the reversed flow disappears after some calculation time - I would try to get a better continuity than 1e-2. hope that helps

 April 19, 2007, 05:40 Re: reversed flow #3 Vivek Vasudevan Guest   Posts: n/a Hi, I too get reversed flow warnings on a few faces on my pressure-outlet boundary. Problem is that the residuals for continuity, x, y and z velocities oscillates / almost stabilizes around 1, 0.01, 0.01 and 0.1 respectively. How do I improve the residual values? I have checked the flow conditions and they appear reasonable. Do I need to change the relaxation parameters or make an improved gauge pressure estimate during initialization? How do I enlarge the calculation area? The backflow outlet is a region of interest as I would need the pressure drop across the inlet and outlet boundaries. Please advise. Thanks, Vivek

 April 19, 2007, 06:28 Re: reversed flow #4 Gernot Guest   Posts: n/a To enlarge the calculation area is easy ( in most cases ). Where does your fluid go after leaving the outlet? Apend another volume to simulate this and make this volume that big that the backflow at the new outlet(s) does not influence your old one. Set the old outlet as interior and you can get all the values you need out of it. I know that this is also a question of cell quantity and there are always facts that might make this impossible but i think in most cases it works. If you really make it like i told you I can help you to save time for the new calculation by using the `oldī results as starting conditions.( if youīr interested in ) mfg Gernot

 April 19, 2007, 12:16 Re: reversed flow #5 Nak Guest   Posts: n/a Attach similar extension volumes to the inlet and outlet boundaries, set-up the case, "INTERPOLATE" the data from previous case and re-run the case again. Right Gernot ? ;-) Nak.

 April 20, 2007, 01:12 Re: reversed flow #6 Gernot Guest   Posts: n/a Yes thats exactly what I mean.

 April 22, 2007, 07:37 Re: reversed flow #7 masoud Guest   Posts: n/a hello: this case is normal in flow pattern and is not harmful.

 April 23, 2007, 01:04 Re: reversed flow #8 mvee Guest   Posts: n/a ya but after running so many interations still revrsed flow message exists and problem does not converge. my momentum underrelaxation factor is 0.3.

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