Changing boundary condition Ux after fluid reaches a specific distance

mcfdma · November 19, 2019, 05:23

Hello. I am working on filling the capillary with fluid.

The flow rate (Ux) is slow and the capillary is long which results in taking significant amount of time to fill the entire capillary.

Is there a way to speed up this process by initially setting the Ux to be high (higher than the value needed for the case) and once it reaches a particular distance in x coordinate, the Ux value is reduced automatically without me stopping the case and manually reducing the Ux and re-running it.

I have been looking at codedFixedValue but not sure.
Any help?

einstein_zee · November 19, 2019, 10:03

Hi there,

you may find this one useful How to correctly show the result of #codeStream# internalField?

raumpolizei · November 21, 2019, 03:52

Hey
I don't know your specific case but this sounds like this could be estimated by hand. With codedFixedValue, you are on the right track. Based on what you wrote there are a few other options you may want to try out:

GroovyBC - check if swak4foam is available for your OF version. You could prescribe a ramp for the inflow velocity.
Also, depending on your domain, you may want to have a look at funkysetfields (also a swak4foam utility).
This wont solve you problem but you could use a coarse mesh and run the case until you are reaching the state of interest. Or a bit before if the case is turbulent in order to allow turbulence to evolve. Map it to the fine mesh and continue your simulations (mapFields).
Write a bash script for the whole case, including the velocity change (use foamDictionary and similar commands).

Good luck!
RP

November 19, 2019, 05:23	Changing boundary condition Ux after fluid reaches a specific distance	#1
mcfdma Member X Join Date: Jan 2019 Posts: 63 Rep Power: 7	Hello. I am working on filling the capillary with fluid. The flow rate (Ux) is slow and the capillary is long which results in taking significant amount of time to fill the entire capillary. Is there a way to speed up this process by initially setting the Ux to be high (higher than the value needed for the case) and once it reaches a particular distance in x coordinate, the Ux value is reduced automatically without me stopping the case and manually reducing the Ux and re-running it. I have been looking at codedFixedValue but not sure. Any help?

November 21, 2019, 03:52		#3
raumpolizei Member Join Date: Dec 2018 Location: Darmstadt, Germany Posts: 87 Rep Power: 7	Hey I don't know your specific case but this sounds like this could be estimated by hand. With codedFixedValue, you are on the right track. Based on what you wrote there are a few other options you may want to try out: GroovyBC - check if swak4foam is available for your OF version. You could prescribe a ramp for the inflow velocity. Also, depending on your domain, you may want to have a look at funkysetfields (also a swak4foam utility). This wont solve you problem but you could use a coarse mesh and run the case until you are reaching the state of interest. Or a bit before if the case is turbulent in order to allow turbulence to evolve. Map it to the fine mesh and continue your simulations (mapFields). Write a bash script for the whole case, including the velocity change (use foamDictionary and similar commands). Good luck! RP

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November 19, 2019, 10:03		#2
einstein_zee Member Hosein Join Date: Nov 2011 Location: Germany Posts: 93 Rep Power: 14	Hi there, you may find this one useful How to correctly show the result of #codeStream# internalField?