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Post Processing Results: Ansys Workbench 18.2 - Fluent - CFD Post - Porous Body

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Old   April 28, 2021, 07:15
Default Post Processing Results: Ansys Workbench 18.2 - Fluent - CFD Post - Porous Body
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OnlyCFD
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Hi,

I am new to ANSYS and trying hands at Fluent and CFD Post.

Working on ANSYS Workbencj 18.2, have a question on how the CFD Post processes the results of the runs performed in FLUENT.

Have shown a simple case in the image file attached.

What we have in here is inlets from 2 sides, a porous body ( coefficients attached from experimental data, viscous and inertial resistances) and and one outlet on the top.

Air enters from 2 inlets, turn 90 degrees, enter the porous body and then from the exit side of the porous body, will move towards the outlet.

Model is fully converged and mass balance is correct.

When the data is postprocessed in CFD Post to understand the velocity field on the inlet to the porous body, noticed two variations of plots.

The top velocity plot in the attached image is the velocity plot on the inlet surface of the porous body

Bottom velocity plot is a velocity plot at 0.1 inch in front of the inlet surface of porous body

Herein is my confusion.

As soon as the plane of velocity plot is moved away from the inlet surface of porous body, there is a an order of magnitude change in velocity ?

Is it realistic ?

Are we plotting the velocity correctly at different locations ?

Any help or guidance would be of great help
Attached Images
File Type: jpg Porous Body Q.JPG (87.6 KB, 14 views)
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Old   April 28, 2021, 08:23
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Glenn Horrocks
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FAQ: https://www.cfd-online.com/Wiki/Ansy..._inaccurate.3F

The FAQ was written for CFX but holds just as well for Fluent as well.

For details on the Fluent solver please post on the Fluent forum.

But some suggestions:
- Visualise the flow better by drawing streamlines. Decide whether the streamlines are realistic.
- Also velocity vectors are good to understand the flow.
- You have your inlets right next to the porous regions. This means the area around the porous region near the inlet is going to be affected by whatever you define your inlet condition to be. You might need to move this inlet further away.
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Old   April 28, 2021, 08:40
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Thanks a lot Glenn for the reply.

I tried to get attention in Fluent Forum. No response. Probably lost in Volume of messages there. Will try again.

Inlet are at static pressure 0 and outlet side, have a fan.

Hope this helps
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Old   April 28, 2021, 18:43
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We are not the fall-back forum for when the Fluent forum fails to answer. To get information about Fluent you need to post on the Fluent forum.

My comment about the inlets being too close still looks to be a major problem in your simulation.
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Old   April 29, 2021, 03:02
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It all depends on the pressure drop over the porous plate, the mesh type and size, the position of the inlets etc. So it is difficult to say it this is realistic. Suggestions:

- What meshtype and size do you have over the thickness of the porous plate?
- What is the pressure drop? What resistance model is it?
- I would look at the components of the velocity, not just the magnitude.
- Did you make a plane through inlet and porous plate and investigated the velocity and the velocity components? Why not plot vectors?
- As Glenn mentioned, did you investigate streamlines?

Regs, Gert-Jan
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