making a decision about BC

icem_god · March 4, 2020, 03:04

Hello

my question is about BC dilemma.

I have a ducted fan. it has his rpms and perfomance curve obtained through massflow throttling.

so now i`ve tried to simulate such task - i want to put this fan onto a big domain like its hanging in the air. So the fan is going to have only it`s rpms and atmospheric pressure of the air.

Does somebody have any idea which BCs I need to use for this big domain?
I`ve tried to use Opening for all the faces of domain but I`ve reached something really strange.

icem_god · March 4, 2020, 03:26

so the main question is - can I somehow tell the solver that this big domain is atmosphere?
or I need to determine all the pressures from each side of domain manually by myself?

ghorrocks · March 4, 2020, 18:07

If the fan has its entrance and exit inside the domain then use a source term. If the fan makes air enter or leave the domain then use an inlet or an outlet. Then set the source term, inlet or outlet up to have the pressure difference follow the mass flow rate curve from the performance curve.

Your second post is puzzling. If you do not model gravity then model atmosphere by an opening with pressure =0. If you are modelling gravity then make sure you have your reference pressures and density set correctly and you can still use an opening with pressure =0.

icem_god · March 5, 2020, 01:26

Quote:

Originally Posted by ghorrocks

If the fan has its entrance and exit inside the domain then use a source term. If the fan makes air enter or leave the domain then use an inlet or an outlet. Then set the source term, inlet or outlet up to have the pressure difference follow the mass flow rate curve from the performance curve.

Your second post is puzzling. If you do not model gravity then model atmosphere by an opening with pressure =0. If you are modelling gravity then make sure you have your reference pressures and density set correctly and you can still use an opening with pressure =0.

Thank you for your reply!

I do not model gravity. I`ve used Opening Pressure 0 with Entrainment option for all faces of the atmospheric domain and achieved some bad results. Maybe my opening option is not so good

ghorrocks · March 5, 2020, 01:38

Try a pressure opening without the entrainment option.

basivi · March 8, 2020, 21:27

I might help, but I did not understand your question properly. Please check the attachment.

Note: I used opening boundary condition at the outlet also.

icem_god · March 10, 2020, 03:40

Quote:

Originally Posted by basivi

I might help, but I did not understand your question properly. Please check the attachment.

Note: I used opening boundary condition at the outlet also.

Thank you!
Glenn`s advice already worked - my problem was about Entrainment pressure option of opening boundary

March 4, 2020, 03:04	making a decision about BC	#1
icem_god New Member Join Date: Nov 2017 Posts: 22 Rep Power: 8	Hello my question is about BC dilemma. I have a ducted fan. it has his rpms and perfomance curve obtained through massflow throttling. so now i`ve tried to simulate such task - i want to put this fan onto a big domain like its hanging in the air. So the fan is going to have only it`s rpms and atmospheric pressure of the air. Does somebody have any idea which BCs I need to use for this big domain? I`ve tried to use Opening for all the faces of domain but I`ve reached something really strange.

March 4, 2020, 18:07		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	If the fan has its entrance and exit inside the domain then use a source term. If the fan makes air enter or leave the domain then use an inlet or an outlet. Then set the source term, inlet or outlet up to have the pressure difference follow the mass flow rate curve from the performance curve. Your second post is puzzling. If you do not model gravity then model atmosphere by an opening with pressure =0. If you are modelling gravity then make sure you have your reference pressures and density set correctly and you can still use an opening with pressure =0. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

March 5, 2020, 01:38		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,700 Rep Power: 143	Try a pressure opening without the entrainment option. icem_god likes this. __________________ Note: I do not answer CFD questions by PM. CFD questions should be posted on the forum.

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March 4, 2020, 03:26		#2
icem_god New Member Join Date: Nov 2017 Posts: 22 Rep Power: 8	so the main question is - can I somehow tell the solver that this big domain is atmosphere? or I need to determine all the pressures from each side of domain manually by myself?