simulating Creeping flow with Reynolds number 5e-9

fan li · December 19, 2018, 17:54

Hi every one

I have to simulate the steady creeping flow with Reynolds number 5e-9. I have managed to simulated similar case with Reynolds number 0.1 in fluent, but Fluent has convergence problem as Reynolds number decreases to 1e-7 (Fluent converged in one iteration). I have read the post

Simulating Creeping (Stokes) Flow in OpenFOAM

where the creeping flow with Reynolds number 0.001 can be simulated by Openfoam. But I do not know if Openfoam can simulate the Reynolds number 5e-9 I want?

If fluent and Openfoam can not simulate the steady creeping flow with Reynolds number 5e-9, any other CFD softwares can do it?

Thanks

Fan

LuckyTran · December 20, 2018, 00:50

Creeping flows are a piece of cake for both Fluent and OpenFOAM.

Convergence in 1 iteration just means you need to turn off the convergence monitors.

If you have divergence problems then you might need to tweak some solver settings, but there's no limitation or reason why Fluent/OpenFOAM can't solve creeping flows.

AliE · December 20, 2018, 04:05

Hi, I agree with LuckyTran. In OF, I have solved several problems disabling convective term (i.e.solving stokes equation). For a such low Re, you can have some issues related to the viscous stabilty, which forces your time step to be lower, but theoretically there are no reason for which they will not work!

fan li · December 20, 2018, 07:59

Hi LuckyTran

It works after I turned off the convergence monitors.

fan li · December 20, 2018, 08:10

Hi AliE

Could you please tell me more about how to disable convective term in fluent?

AliE · December 20, 2018, 08:11

Well unfortunatelly I cannot be useful here, sicne I have done it only in OF. Not sure you can change the code at this level in fluent. Maybe LuckyTran in more expert than me in fluent!

LuckyTran · December 20, 2018, 12:12

Disabling the advective/convection term only is not really a feature in Fluent. You would have to find a nasty workaround. I would recommend to use OpenFOAM if you want to solve the Stokes equations. Fluent solves the compressible Navier-Stokes and it's really hard to get it to do anything other than that.

FMDenaro · December 20, 2018, 12:45

Maybe using the NITA method for incompressible flows and setting an high value for the kinematic viscosity using the characteristic velocity of 1 m/s and the lenght of 1m you have implicitly this feature.

December 19, 2018, 17:54	simulating Creeping flow with Reynolds number 5e-9	#1
fan li New Member Join Date: Dec 2018 Posts: 4 Rep Power: 8	Hi every one I have to simulate the steady creeping flow with Reynolds number 5e-9. I have managed to simulated similar case with Reynolds number 0.1 in fluent, but Fluent has convergence problem as Reynolds number decreases to 1e-7 (Fluent converged in one iteration). I have read the post Simulating Creeping (Stokes) Flow in OpenFOAM where the creeping flow with Reynolds number 0.001 can be simulated by Openfoam. But I do not know if Openfoam can simulate the Reynolds number 5e-9 I want? If fluent and Openfoam can not simulate the steady creeping flow with Reynolds number 5e-9, any other CFD softwares can do it? Thanks Fan

December 20, 2018, 00:50		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	Creeping flows are a piece of cake for both Fluent and OpenFOAM. Convergence in 1 iteration just means you need to turn off the convergence monitors. If you have divergence problems then you might need to tweak some solver settings, but there's no limitation or reason why Fluent/OpenFOAM can't solve creeping flows. AliE likes this.

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December 20, 2018, 04:05		#3
AliE Senior Member Join Date: Dec 2017 Posts: 153 Rep Power: 8	Hi, I agree with LuckyTran. In OF, I have solved several problems disabling convective term (i.e.solving stokes equation). For a such low Re, you can have some issues related to the viscous stabilty, which forces your time step to be lower, but theoretically there are no reason for which they will not work!

December 20, 2018, 07:59		#4
fan li New Member Join Date: Dec 2018 Posts: 4 Rep Power: 8	Hi LuckyTran It works after I turned off the convergence monitors.

December 20, 2018, 08:10		#5
fan li New Member Join Date: Dec 2018 Posts: 4 Rep Power: 8	Hi AliE Could you please tell me more about how to disable convective term in fluent?

December 20, 2018, 08:11		#6
AliE Senior Member Join Date: Dec 2017 Posts: 153 Rep Power: 8	Well unfortunatelly I cannot be useful here, sicne I have done it only in OF. Not sure you can change the code at this level in fluent. Maybe LuckyTran in more expert than me in fluent!

December 20, 2018, 12:12		#7
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,761 Rep Power: 66	Disabling the advective/convection term only is not really a feature in Fluent. You would have to find a nasty workaround. I would recommend to use OpenFOAM if you want to solve the Stokes equations. Fluent solves the compressible Navier-Stokes and it's really hard to get it to do anything other than that.

December 20, 2018, 12:45		#8
FMDenaro Senior Member Filippo Maria Denaro Join Date: Jul 2010 Posts: 6,896 Rep Power: 73	Maybe using the NITA method for incompressible flows and setting an high value for the kinematic viscosity using the characteristic velocity of 1 m/s and the lenght of 1m you have implicitly this feature.