Reverse Flow

Musa · February 28, 2012, 20:32

Hi I am simulating a gas-solid fluidized bed and I am receiving a message " reverse flow on x faces at pressure outlet y. My boundary conditions are velocity inlet and pressure outlet.

tichaona · February 29, 2012, 01:29

I have had the same message from my simulation. You can take it out by replacing your pressure outlet boundary with outflow boundary if you want to. Also reversed flow may be actually ocurring in your real problem. How many cells have the reversed flow? If the number is small when compared to total number of cells, then it does not matter much. Is the reversed flow message appearing throghout your calculations or is it just appearing initially and then disappears. If it disappears then its ok.

Hope this may help you.

Zigainer · February 29, 2012, 01:35

I get reverse flow quite often with pressure outlet, but if the reverse flow dissapears ... so thats fine
Otherwise start with first order and lower under-relaxation factors for a couple of iterations and than change the relaxation factors and switch to 2nd order.

Musa · February 29, 2012, 05:17

Tichaona and Zigainer thank you for your suggestions. I will try them out

delaneyluke · February 29, 2012, 06:51

Another suggestion might be to extend your outlet to a location when there is no recirculation.

Regards
Luke

Musa · February 29, 2012, 07:13

Delaneyluke what exactly do you mean by extending the outlet?

delaneyluke · February 29, 2012, 07:17

Extend the mesh/domain at the outlet and your outlet BC will shift to the extended outlet. This is done because it is generally unadvisable to have your outlet at a location where there is recirculating flow. But again this is done on a case-to-case basis. It depends on whether the location of recirculation at your outlet is a region of interest to your analysis. If it is not then you can ignore the reverse flow warning.
Regards
Luke

February 28, 2012, 20:32	Reverse Flow	#1
Musa Member Musango Lungu Join Date: Dec 2011 Location: China Posts: 73 Rep Power: 14	Hi I am simulating a gas-solid fluidized bed and I am receiving a message " reverse flow on x faces at pressure outlet y. My boundary conditions are velocity inlet and pressure outlet.

February 29, 2012, 01:29	reversed flow	#2
tichaona New Member tichaona Join Date: Dec 2011 Location: South Africa Posts: 13 Rep Power: 14	I have had the same message from my simulation. You can take it out by replacing your pressure outlet boundary with outflow boundary if you want to. Also reversed flow may be actually ocurring in your real problem. How many cells have the reversed flow? If the number is small when compared to total number of cells, then it does not matter much. Is the reversed flow message appearing throghout your calculations or is it just appearing initially and then disappears. If it disappears then its ok. Hope this may help you.

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February 29, 2012, 01:35		#3
Zigainer Senior Member Join Date: May 2011 Location: Germany Posts: 130 Rep Power: 14	I get reverse flow quite often with pressure outlet, but if the reverse flow dissapears ... so thats fine Otherwise start with first order and lower under-relaxation factors for a couple of iterations and than change the relaxation factors and switch to 2nd order.

February 29, 2012, 05:17		#4
Musa Member Musango Lungu Join Date: Dec 2011 Location: China Posts: 73 Rep Power: 14	Tichaona and Zigainer thank you for your suggestions. I will try them out

February 29, 2012, 06:51		#5
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	Another suggestion might be to extend your outlet to a location when there is no recirculation. Regards Luke

February 29, 2012, 07:13		#6
Musa Member Musango Lungu Join Date: Dec 2011 Location: China Posts: 73 Rep Power: 14	Delaneyluke what exactly do you mean by extending the outlet?

February 29, 2012, 07:17		#7
delaneyluke Senior Member Join Date: Mar 2009 Location: Indiana, US Posts: 186 Rep Power: 17	Extend the mesh/domain at the outlet and your outlet BC will shift to the extended outlet. This is done because it is generally unadvisable to have your outlet at a location where there is recirculating flow. But again this is done on a case-to-case basis. It depends on whether the location of recirculation at your outlet is a region of interest to your analysis. If it is not then you can ignore the reverse flow warning. Regards Luke