[ANSYS Meshing] [ANSYS Meshing] Fixing high skewness on simple elbow pipe

luzikato · May 6, 2020, 08:06

Hello.

I have an assignment to simulate airflow on a simple elbow as shown below. My professor wants me to simulate this on a structured mesh, so I find a random tutorial on youtube to make this happen. Here's the link: https://www.youtube.com/watch?v=1woKtFjN-bE&t=525s

I followed that tutorial and made some improvements according to my geometry and also made quite a smooth mesh (I think).
But when I checked the skewness quality, it shows some elements have skewness above 0.99. I managed to find the bad elements on my geometry but still can't figure out how to fix those elements.

I've done some research and most of them gave solution to add more elements to the bad area but had no effect on the skewness.

Before I wrote this question, I tried to force it to run on fluent and the console gave me errors such as :
1. Turbulent viscosity limited to viscosity ratio of 1.000000e+05 in xxx cells.
2. Reversed flow in 77 faces on outflow 12.

Before I ran the case I also checked the case, it says I have skewness of 0.99 and it needs to be fixed. I assume this also can affect my solution.

Is there any way to fix my mesh? I also attached my project files below.

The deadline is next week, but I do appreciate the fast reply. And also, is there any reference I can use to learn any meshing technique, strategy, and problem-solving?

Thank you in advance.
Best regards.

Capture.JPG Capture2.jpg Capture3.jpg

https://drive.google.com/file/d/1Ci-...ew?usp=sharing

siw · May 7, 2020, 08:24

"...and made some improvements according to my geometry and also made quite a smooth mesh (I think)".

I highlighted a big jump in cell size, not what I would call smooth. Rule of thumb is cell size transition should be below about 20%, unless nothing is happening e.g. farfield in aerodynamics CFD. Here your flow is entering the bend so flow gradients will be occurring.

You do not need to split the geometry. Use MultiZone and Inflation. I made a quick test model and got a maximum skewness of 0.59. I guessed the sizes so you'll need to make for yourself.

luzikato · May 10, 2020, 02:34

Thank you siw for the advices.

Fortunately, I managed to fix the problem by changing the inflation to smooth transition and also made mesh with 0.55 skewness.

I made a few different settings and at some point I checked the quality, suddenly tet mesh appeared, when I turn it to my first setting the tet mesh still present. When I change mesh setting I always use "Update" button and when I clear the generated mesh data and regenerate it somehow the tet mesh disappeared again. Not just that, the skewness problem also fixed. I'm confused, is this usually happening?

Thanks,
Best regards

May 6, 2020, 08:06	[ANSYS Meshing] Fixing high skewness on simple elbow pipe	#1
luzikato New Member Anas Nur Fauzan Join Date: Oct 2019 Posts: 18 Rep Power: 6	Hello. I have an assignment to simulate airflow on a simple elbow as shown below. My professor wants me to simulate this on a structured mesh, so I find a random tutorial on youtube to make this happen. Here's the link: https://www.youtube.com/watch?v=1woKtFjN-bE&t=525s I followed that tutorial and made some improvements according to my geometry and also made quite a smooth mesh (I think). But when I checked the skewness quality, it shows some elements have skewness above 0.99. I managed to find the bad elements on my geometry but still can't figure out how to fix those elements. I've done some research and most of them gave solution to add more elements to the bad area but had no effect on the skewness. Before I wrote this question, I tried to force it to run on fluent and the console gave me errors such as : 1. Turbulent viscosity limited to viscosity ratio of 1.000000e+05 in xxx cells. 2. Reversed flow in 77 faces on outflow 12. Before I ran the case I also checked the case, it says I have skewness of 0.99 and it needs to be fixed. I assume this also can affect my solution. Is there any way to fix my mesh? I also attached my project files below. The deadline is next week, but I do appreciate the fast reply. And also, is there any reference I can use to learn any meshing technique, strategy, and problem-solving? Thank you in advance. Best regards. Capture.JPG Capture2.jpg Capture3.jpg https://drive.google.com/file/d/1Ci-...ew?usp=sharing

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May 10, 2020, 02:34		#3
luzikato New Member Anas Nur Fauzan Join Date: Oct 2019 Posts: 18 Rep Power: 6	Thank you siw for the advices. Fortunately, I managed to fix the problem by changing the inflation to smooth transition and also made mesh with 0.55 skewness. I made a few different settings and at some point I checked the quality, suddenly tet mesh appeared, when I turn it to my first setting the tet mesh still present. When I change mesh setting I always use "Update" button and when I clear the generated mesh data and regenerate it somehow the tet mesh disappeared again. Not just that, the skewness problem also fixed. I'm confused, is this usually happening? Thanks, Best regards