continuity residual problem

flow_CH · July 1, 2013, 05:35

HI.

I am modeling channel with two inlet (water+air) with velocity inlet for inlets and pressure outlet for outlet boundary.
But in solving, i am trying for 2000 iteration and more but continuity residual does not cross down of continuity criteria ( 0.001) and solving is keeping and not stop.
Can you help me?
please see attached image

flow_CH · July 19, 2013, 02:41

please help

ishanv · July 19, 2013, 06:24

are you using any urf for density? Just set it to 1

flow_CH · July 19, 2013, 06:28

No. I am not using urf.The density for air and water is constant.

vasava · July 22, 2013, 06:04

You can try refining your mesh. Also increase the order of discretization.

robboflea · July 22, 2013, 12:08

It may be that there's absolutely nothing wrong with your simulation. The values of the residuals is scaled with the residuals at the start of the calculation. If your initial guess was particularly good then residuals won't drop so much but still you will have a physically valid result.

If residuals are stable for a long number of iterations and other physical parameters of interest in your simulation (in your case maybe the pressure drop across the pipe could be one) are stable too and the results do not show anything clearly wrong then I guess you can consider your simulation correct.

flotus1 · July 23, 2013, 02:46

To gain insight if robbofleas statment applies to your case, you can switch your simulation to double precision. Then the residuals should drop further.

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July 19, 2013, 02:41		#2
flow_CH Senior Member FHydro Join Date: Jan 2013 Posts: 197 Rep Power: 13	please help

July 19, 2013, 06:24		#3
ishanv New Member ishan verma Join Date: May 2012 Posts: 1 Rep Power: 0	are you using any urf for density? Just set it to 1

July 19, 2013, 06:28		#4
flow_CH Senior Member FHydro Join Date: Jan 2013 Posts: 197 Rep Power: 13	No. I am not using urf.The density for air and water is constant.

July 22, 2013, 06:04		#5
vasava Senior Member Paritosh Vasava Join Date: Oct 2012 Location: Lappeenranta, Finland Posts: 732 Rep Power: 22	You can try refining your mesh. Also increase the order of discretization.

July 22, 2013, 12:08		#6
robboflea Senior Member Join Date: Nov 2011 Posts: 109 Rep Power: 14	It may be that there's absolutely nothing wrong with your simulation. The values of the residuals is scaled with the residuals at the start of the calculation. If your initial guess was particularly good then residuals won't drop so much but still you will have a physically valid result. If residuals are stable for a long number of iterations and other physical parameters of interest in your simulation (in your case maybe the pressure drop across the pipe could be one) are stable too and the results do not show anything clearly wrong then I guess you can consider your simulation correct.

July 23, 2013, 02:46		#7
flotus1 Super Moderator Alex Join Date: Jun 2012 Location: Germany Posts: 3,399 Rep Power: 46	To gain insight if robbofleas statment applies to your case, you can switch your simulation to double precision. Then the residuals should drop further.