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Note: This discussion is about an older version of the COMSOL Multiphysics® software. The information provided may be out of date.

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Boundaries not applicable (fluid flow in pipe)

Posted Nov 12, 2019, 7:52 p.m. EST Fluid & Heat, Computational Fluid Dynamics (CFD), Results & Visualization Version 4.4 2 Replies

Jacob Hawkins
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To anyone and everyone,

I created a pipe using the sweep feature. I can apply inner boundaries for the fluid, but when i look at my wall boundary conditions, all of the outside boudaries of the pipe are not applicable. I went ahead and ran the simulation at about 80GPM and looked at the velocity diagram and the numbers seem way too low, but i dont know if the boundaries are the problem. Also, I have 2 legends on my diagram and dont know how to get rid of one. please help, Im very new to this. I attached the file and pictures,so yall can take a look.

Thank You!

-Jacob

2 Replies Last Post Nov 13, 2019, 8:28 a.m. EST
Sergei Yushanov Certified Consultant
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Posted: 4 years ago Nov 13, 2019, 8:25 a.m. EST
Updated: 4 years ago Nov 13, 2019, 3:25 a.m. EST

Jacob,

  1. Two legends because you have Slice and Multislice for one Velocity plot group. To get rid of one, just clear "Color legend" box for one plot.

  2. Default "Wall" boundary condition node is applicable to the exterior fluid bounaries only and not applicable to the structural boundaries. So, there is nothing wrong that structural boundaries are laabeled as "(not applicable)".

  3. You maximum velocity is 3.76 mm/s which is in agreement with the specified volumetric flow rate of Q=80[gal/min] =0.00505[m^3/s]. To verify this , you can calculate average inlet velocity analytically (see Parameters node in the attached mph file) and compare it to average velocity obtained from your Comsol model V_ave=aveop1(spf.U). Results are in agreement very well, as shown in the attached image.

Regards

Sergei

Jacob, 1. Two legends because you have Slice and Multislice for one Velocity plot group. To get rid of one, just clear "Color legend" box for one plot. 2. Default "Wall" boundary condition node is applicable to the exterior fluid bounaries only and not applicable to the structural boundaries. So, there is nothing wrong that structural boundaries are laabeled as "(not applicable)". 3. You maximum velocity is 3.76 mm/s which is in agreement with the specified volumetric flow rate of Q=80[gal/min] =0.00505[m^3/s]. To verify this , you can calculate average inlet velocity analytically (see Parameters node in the attached mph file) and compare it to average velocity obtained from your Comsol model V_ave=aveop1(spf.U). Results are in agreement very well, as shown in the attached image. Regards Sergei
Jeff Hiller COMSOL Employee

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Posted: 4 years ago Nov 13, 2019, 8:28 a.m. EST
Updated: 4 years ago Nov 13, 2019, 3:28 a.m. EST

Hello Jacob,

Those surfaces are not applicable because they do not touch the region where the PDEs are being solved. In other words, you can't apply a boundary condition to a surface that's not a boundary of the computational domain.

Regarding the two color legends: one comes from each of the two plots inside your plot group. The GUI lets you turn them off individually if you'd like, see screenshot attached.

Best,

Jeff!

-------------------
Jeff Hiller
Hello Jacob, Those surfaces are not applicable because they do not touch the region where the PDEs are being solved. In other words, you can't apply a boundary condition to a surface that's not a boundary of the computational domain. Regarding the two color legends: one comes from each of the two plots inside your plot group. The GUI lets you turn them off individually if you'd like, see screenshot attached. Best, Jeff!

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