Meshing edges in Star CCM+ for CFD simulation.

Sai1996 · June 4, 2022, 08:36

I am doing a CFD study on a bluff body to study the drag variation. During the meshing process in Starccm+, I came across a stage where the mesh does end smoothly at the edge (see figures).

I have personally tried the following techniques:

1) Specifying the size at the feature curve but still I get the the weird shape at the edge.

2) meshing by created a seperate volume.

Which option could help me get over this?

koful · June 10, 2022, 12:15

Hi Sai,

Mesher is reducing the thickness of the prism layer because this layered surface is attached to a non-layered surface.
Wyh did not you mesh inside the body and why did you disable prism layer for back side of the body? If it is not a CHT case, you do not need to mesh solid regions. Substract the inner body and mesh the rest. Enable prism layer for all wall boundaries.

cwl · June 11, 2022, 15:26

Quote:

I came across a stage where the mesh does end smoothly at the edge (see figures)

How should it be meshed in your opinion?

Sai1996 · June 12, 2022, 09:08

First of all, sorry that was a typo. I wanted to state that the mesh does not end smoothly.
I wanted to know like how do I mesh it such that there is a smoother transition from prism layers to the other bulk of the mesh?

Sai1996 · June 12, 2022, 09:09

other bulk of the mesh?

Sai1996 · June 12, 2022, 09:13

Quote:

Originally Posted by koful

Hi Sai,

Mesher is reducing the thickness of the prism layer because this layered surface is attached to a non-layered surface.
Wyh did not you mesh inside the body and why did you disable prism layer for back side of the body? If it is not a CHT case, you do not need to mesh solid regions. Substract the inner body and mesh the rest. Enable prism layer for all wall boundaries.

actually, I do not need a prism layer behind the body since, I am meshing the wake of the bluff body seperately with specified size. My goal is to get a smoother transition from layered to un layered.

cwl · June 12, 2022, 12:55

Once again: how should it be meshed in your opinion? - Just draw it in Paint or whatever.

Sai1996 · June 13, 2022, 09:56

Quote:

Originally Posted by cwl

Once again: how should it be meshed in your opinion? - Just draw it in Paint or whatever.

Basically here i need a smooth transition.

Aeronautics El. K. · June 25, 2022, 04:57

Seems like you haven't checked or tried the options that the prism layer mesher gives you.
I'd start there.

Sai1996 · June 25, 2022, 10:49

Quote:

Originally Posted by Aeronautics El. K.

Seems like you haven't checked or tried the options that the prism layer mesher gives you.
I'd start there.

Maybe instead of voicing bland comments if you could sugest me something that would be great.
I have explored the prism layer options in the Star CCM+ such as the minimum thickness percentage and layer reduction percentage. These were the main parameters affecting those edge layers. What else can I do more?

Aeronautics El. K. · June 26, 2022, 05:43

Quote:

Originally Posted by Sai1996

Maybe instead of voicing bland comments if you could sugest me something that would be great.
I have explored the prism layer options in the Star CCM+ such as the minimum thickness percentage and layer reduction percentage. These were the main parameters affecting those edge layers. What else can I do more?

You're right, seems like you're ahead of me.
I don't know the answer, sorry.

Cheers.

ashokac7 · June 28, 2022, 02:13

Mesh looks okay to me. Mesh you have shown is worst than what we already have. Still if you want more control, create surfaces along the body and apply different prism layer controls to them. Since you are connecting surface with prisms to surface without prism layers, it has to have transition somewhere. I would say don't go on the looks. By the looks of it, polyhedral is very ugly sometimes but works great.

June 25, 2022, 04:57		#9
Aeronautics El. K. Senior Member Lefteris Join Date: Oct 2011 Location: UK Posts: 341 Rep Power: 16	Seems like you haven't checked or tried the options that the prism layer mesher gives you. I'd start there. __________________ Lefteris

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June 10, 2022, 12:15		#2
koful Member Join Date: Jun 2014 Location: Turkey Posts: 58 Rep Power: 12	Hi Sai, Mesher is reducing the thickness of the prism layer because this layered surface is attached to a non-layered surface. Wyh did not you mesh inside the body and why did you disable prism layer for back side of the body? If it is not a CHT case, you do not need to mesh solid regions. Substract the inner body and mesh the rest. Enable prism layer for all wall boundaries.

June 12, 2022, 09:08		#4
Sai1996 New Member Sai Teja Join Date: Jun 2022 Posts: 6 Rep Power: 4	First of all, sorry that was a typo. I wanted to state that the mesh does not end smoothly. I wanted to know like how do I mesh it such that there is a smoother transition from prism layers to the other bulk of the mesh?

June 12, 2022, 09:09		#5
Sai1996 New Member Sai Teja Join Date: Jun 2022 Posts: 6 Rep Power: 4	other bulk of the mesh?

June 12, 2022, 12:55		#7
cwl Senior Member Chaotic Water Join Date: Jul 2012 Location: Elgrin Fau Posts: 438 Rep Power: 18	Once again: how should it be meshed in your opinion? - Just draw it in Paint or whatever.

June 28, 2022, 02:13		#12
ashokac7 Senior Member Ashok Chaudhari Join Date: Aug 2016 Location: Pune, India Posts: 260 Rep Power: 11	Mesh looks okay to me. Mesh you have shown is worst than what we already have. Still if you want more control, create surfaces along the body and apply different prism layer controls to them. Since you are connecting surface with prisms to surface without prism layers, it has to have transition somewhere. I would say don't go on the looks. By the looks of it, polyhedral is very ugly sometimes but works great.