Mesh independent study

santhoshb96 · February 21, 2019, 12:18

I am trying to model a flow over an airfoil. While doing mesh independence study, the value of Cl does not seem to converge to a particular value when I reduce the mesh size. I get fluctuating results during the process. What might be wrong in the process?

LuckyTran · February 22, 2019, 09:54

Probably you don't maintain consistent mesh topology / mesh quality as you change you cell size. This is why it's important to always do these mesh dependence studies. Sometimes (always), a lot more things are changing than you think. It's also why it's better to call them mesh dependence or mesh sensitivity studies. Because the idea that the solution is actually independent of the mesh is quite absurd.

santhoshb96 · February 23, 2019, 00:14

What you are saying is true. Every time I reduce the mesh size the orthogonal quality and aspect ratio differs slightly. How do I maintain those two parameters while changing mesh size? Thanks for your reply.

Roh · February 23, 2019, 01:28

I don't know what program you use to generate your mesh but "Orthogonal Quality" and "Aspect Ratio" are available in Ansys Meshing. You can check this parameters before transfer your mesh to Fluent. You need to keep the scale of your mesh costant as possible as in your mesh independent study. If you change the bias or scale of your mesh along y axis, then you need to change the bias or scale scale of your mesh along x axis. and keep in mind that before doing mesh dependent study, you need to create a mesh as good as possible using these parameters. You need to learn the definition of both parameters before using them. Thus please read this page to know how to create a decent mesh before doing mesh dependent study:

https://www.sharcnet.ca/Software/Ans...h_quality.html

santhoshb96 · February 23, 2019, 02:15

I am using ANSYS meshing (v19.0). But I dont seee an option to specify orthogonal quality or Aspect ratio. Just an option to view them in quality option. I am doing 2D flow over an airfoil and I just reduce the mesh size by decreasing the overall size of the mesh by face sizing.

February 21, 2019, 12:18	Mesh independent study	#1
santhoshb96 New Member Santhosh Join Date: May 2018 Posts: 5 Rep Power: 7	I am trying to model a flow over an airfoil. While doing mesh independence study, the value of Cl does not seem to converge to a particular value when I reduce the mesh size. I get fluctuating results during the process. What might be wrong in the process?

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February 22, 2019, 09:54		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,672 Rep Power: 65	Probably you don't maintain consistent mesh topology / mesh quality as you change you cell size. This is why it's important to always do these mesh dependence studies. Sometimes (always), a lot more things are changing than you think. It's also why it's better to call them mesh dependence or mesh sensitivity studies. Because the idea that the solution is actually independent of the mesh is quite absurd.

February 23, 2019, 00:14		#3
santhoshb96 New Member Santhosh Join Date: May 2018 Posts: 5 Rep Power: 7	What you are saying is true. Every time I reduce the mesh size the orthogonal quality and aspect ratio differs slightly. How do I maintain those two parameters while changing mesh size? Thanks for your reply.

February 23, 2019, 01:28		#4
Roh Senior Member Join Date: Sep 2017 Posts: 130 Rep Power: 8	I don't know what program you use to generate your mesh but "Orthogonal Quality" and "Aspect Ratio" are available in Ansys Meshing. You can check this parameters before transfer your mesh to Fluent. You need to keep the scale of your mesh costant as possible as in your mesh independent study. If you change the bias or scale of your mesh along y axis, then you need to change the bias or scale scale of your mesh along x axis. and keep in mind that before doing mesh dependent study, you need to create a mesh as good as possible using these parameters. You need to learn the definition of both parameters before using them. Thus please read this page to know how to create a decent mesh before doing mesh dependent study: https://www.sharcnet.ca/Software/Ans...h_quality.html

February 23, 2019, 02:15		#5
santhoshb96 New Member Santhosh Join Date: May 2018 Posts: 5 Rep Power: 7	I am using ANSYS meshing (v19.0). But I dont seee an option to specify orthogonal quality or Aspect ratio. Just an option to view them in quality option. I am doing 2D flow over an airfoil and I just reduce the mesh size by decreasing the overall size of the mesh by face sizing.