# Positive Volumetric Flow showing Negative Pressure

Below is a screenshot of the project that i am working on. I have a Velocity using Volumetric flow of 131 m3/s at cutting plane 1 and pressure outlet with 0 pressure at cutting plane 2. The results are showing Negative pressure which doesn’t make sense. I had a gentlemen that is schooled in CFD look over this and he could not make sense of the results as well. Can someone please tell me what i am doing wrong or tell me how i can get the pressure drop using the information that it is spitting out?

Thank you in advance

Hey there!

Please always include the URL to your project, so we can find out what is happening in detail!

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This is a very interesting case. We will perform some test to discard that the results are not nonphysical.

Could you please tell us a bit about the plenum with embedded elbow device? What is the purpose of this arrange? What is the expected behavior?

The elbow is to act the same as the elbow in a duct for HVAC. We are trying to increase the efficiency of the flow coming from the “Raise” (the vertical shaft) to the “Drift” (the horizontal tunnel) as to decrease the power needed to generate a nominal flow. Normally, in a mine, this room is empty and the air would come directly down the Raise and impact the floor before being pushed down the Drift. The end purpose would be to decrease the amount of power the fan would need to use in order to supply air to the mine.

Hi @bobshawiii,

It seems to be an effect from the mesh, which seems rather coarse to me. For this particular simulation that you are running, I’d suggest using the hex-dominant meshing tool instead with additional fineness (perhaps a fine/very fine configuration).

On a side note, since we have varying cross-sections in this geometry between the inlet and outlet, it would be a better idea to inspect total pressure, rather than static gauge pressure. I noticed that you already have this result control configured in your setup, so that’s very good.

When you run your next simulation, there will be an additional scalar field in the results with the “Total pressure” label:

PS: setting result controls (e.g. area average at the inlet) is also a good idea, to monitor the solution.

Cheers

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I will give that a try. Thank you very much for your assistance and i will update this post once i have the results

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