Two inlets with different fluids

pedroxramos · August 7, 2014, 06:26

Hello,

I am simulating the confluence of two flows of fluids with different density.

How can I define the association between each inlet and each fluid?

Best regards.

JBurnham · August 8, 2014, 18:53

Activate Density Evaluation physics > 1st (or 2nd) order Approximation to Density Transport Equation. Make your mesh block so there is a boundary condition at the main inlet and a different side at the 2nd inlet. Set density on the boundary condition dialog (use velocity or pressure boundary, whichever you have data for). Alternatively, use a mass/momentum source as the inlet of the second channel -instead- of the boundary condition. Either way, specify density.

Akshay · August 11, 2014, 01:33

Hi Jeff

Could you explain why you choose a source instead of a boundary condition for the second channel?

Akshay

JBurnham · August 11, 2014, 12:28

Sure. They do the same thing, essentially. Boundary conditions are maybe a little better because they have more options. That said, the mesh blocks are rectangular, and so it's not always easy to get a channel to a boundary condition.

You might put a second mesh block in to make getting the side channel to a boundary easier (with fewer cells), but then you have inter-block interpolation which can affect conservation of momentum and add uncertainty to the results. In short, if it's not "easy" to get a side channel to the mesh block boundary, then it's better to use a mass-momentum source.

Usually my only consideration when picking a mass-momentum source vs. a mesh block is minimizing the number of mesh blocks and the number of cells - to improve efficiency.

If you use a negative flow rate the mass-momentum source becomes a sink: in that case make sure it's always completely 100% submerged (like on the bed floor, facing up). If it's a source (+ rate) then it can point any direction.

Hope that helps.

Akshay · August 13, 2014, 01:32

Hi Jeff

Yes that does make sense. But when we use a source, we should be more careful in the mesh and resolve the entrance region void of any small distortions at the corners/edges of the entrance region so that there is no disturbed inlet flow that comes in.

kkn1494 · February 10, 2017, 05:49

good morning
my domain consist of 3 different inlets,.
at 1st inlet water
2nd milk
3rd which is open to atomspere
my doubt is how to set this boundry condition in fluent??
wat is the name of milk in fluent material property??

thank you

August 7, 2014, 06:26	Two inlets with different fluids	#1
pedroxramos Member Pedro Ramos Join Date: Mar 2012 Location: Belgium Posts: 81 Rep Power: 14	Hello, I am simulating the confluence of two flows of fluids with different density. How can I define the association between each inlet and each fluid? Best regards. ramakant likes this.

February 10, 2017, 05:49	3 different fluid at 3 different inlet	#6
kkn1494 New Member karthikeyan subramaniam Join Date: Jan 2017 Posts: 6 Rep Power: 9	good morning my domain consist of 3 different inlets,. at 1st inlet water 2nd milk 3rd which is open to atomspere my doubt is how to set this boundry condition in fluent?? wat is the name of milk in fluent material property?? thank you

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August 8, 2014, 18:53		#2
JBurnham Senior Member Jeff Burnham Join Date: Apr 2010 Posts: 204 Rep Power: 17	Activate Density Evaluation physics > 1st (or 2nd) order Approximation to Density Transport Equation. Make your mesh block so there is a boundary condition at the main inlet and a different side at the 2nd inlet. Set density on the boundary condition dialog (use velocity or pressure boundary, whichever you have data for). Alternatively, use a mass/momentum source as the inlet of the second channel -instead- of the boundary condition. Either way, specify density.

August 11, 2014, 01:33		#3
Akshay Member Akshay Kumar Join Date: Aug 2010 Location: India Posts: 84 Rep Power: 15	Hi Jeff Could you explain why you choose a source instead of a boundary condition for the second channel? Akshay

August 11, 2014, 12:28		#4
JBurnham Senior Member Jeff Burnham Join Date: Apr 2010 Posts: 204 Rep Power: 17	Sure. They do the same thing, essentially. Boundary conditions are maybe a little better because they have more options. That said, the mesh blocks are rectangular, and so it's not always easy to get a channel to a boundary condition. You might put a second mesh block in to make getting the side channel to a boundary easier (with fewer cells), but then you have inter-block interpolation which can affect conservation of momentum and add uncertainty to the results. In short, if it's not "easy" to get a side channel to the mesh block boundary, then it's better to use a mass-momentum source. Usually my only consideration when picking a mass-momentum source vs. a mesh block is minimizing the number of mesh blocks and the number of cells - to improve efficiency. If you use a negative flow rate the mass-momentum source becomes a sink: in that case make sure it's always completely 100% submerged (like on the bed floor, facing up). If it's a source (+ rate) then it can point any direction. Hope that helps.

August 13, 2014, 01:32		#5
Akshay Member Akshay Kumar Join Date: Aug 2010 Location: India Posts: 84 Rep Power: 15	Hi Jeff Yes that does make sense. But when we use a source, we should be more careful in the mesh and resolve the entrance region void of any small distortions at the corners/edges of the entrance region so that there is no disturbed inlet flow that comes in.