Inlet diffusion enhances convergence in ansys fluent?

gionin · August 5, 2021, 06:41

Hi everyone,

I'm simulating a cylindrical volume with axis in z-direction. This volume is closed at the top and open at the bottom. It's filled with helium and gravity is applied, with ambient conditions outside of the cylinder (air). I want to simulate the diffusion process in the cylinder.

My setup is as follows:

Pressure-Based, transient simulation, in 2D space with gravity enabled

Energy off
Viscous laminar
Species transport with inlet diffusion enabled

Boundary conditions:
-Pressure outlet with reverse flow
-Cylinder as wall with zero diffusive flux

Method:
SIMPLE

Now my question: No inlet is defined, but still my solution converges much faster with the option "inlet diffusion" enabled. With inlet diffusion disabled it doesn't converge at all. How is that possible?

Thank you for your help.

LuckyTran · August 5, 2021, 13:37

It doesn't have to be an inlet type, stuff just needs to be moving in. Your pressure outlet with reverse flow is an inlet. Even without reverse flow it can still be a species inlet. Stuff can still diffuse inwards even without stuff flowing inwards.

gionin · August 5, 2021, 13:42

Hi LuckyTran
Thank you for your answer.
Ok, I got confused with the different meanings of "inlet".
So my simulation setup and the results should be reasonable considering they correspond quite good to the experimental values.

August 5, 2021, 06:41	Inlet diffusion enhances convergence in ansys fluent?	#1
gionin New Member gionin Join Date: Aug 2021 Posts: 2 Rep Power: 0	Hi everyone, I'm simulating a cylindrical volume with axis in z-direction. This volume is closed at the top and open at the bottom. It's filled with helium and gravity is applied, with ambient conditions outside of the cylinder (air). I want to simulate the diffusion process in the cylinder. My setup is as follows: Pressure-Based, transient simulation, in 2D space with gravity enabled Energy off Viscous laminar Species transport with inlet diffusion enabled Boundary conditions: -Pressure outlet with reverse flow -Cylinder as wall with zero diffusive flux Method: SIMPLE Now my question: No inlet is defined, but still my solution converges much faster with the option "inlet diffusion" enabled. With inlet diffusion disabled it doesn't converge at all. How is that possible? Thank you for your help. Last edited by gionin; August 5, 2021 at 09:01.

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August 5, 2021, 13:37		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,751 Rep Power: 66	It doesn't have to be an inlet type, stuff just needs to be moving in. Your pressure outlet with reverse flow is an inlet. Even without reverse flow it can still be a species inlet. Stuff can still diffuse inwards even without stuff flowing inwards.

August 5, 2021, 13:42		#3
gionin New Member gionin Join Date: Aug 2021 Posts: 2 Rep Power: 0	Hi LuckyTran Thank you for your answer. Ok, I got confused with the different meanings of "inlet". So my simulation setup and the results should be reasonable considering they correspond quite good to the experimental values.