[TGrid] PRISM layer

sarav · February 17, 2010, 09:49

Hi,
I've a problem generating the prism-layer with Tgrid over a 3D wing: the cell-skewness on the trailing edge is very high (more than 0.99).
Who can I solve this problem? which settings do you advise me?
Thanks

udayrg · February 17, 2010, 23:28

hi sarav

Make sure your surface mesh quality is around 0.6 to 0.65 skewness.
And then try to generate prism layers.

Uday

sarav · February 18, 2010, 02:55

Hi!
It's impossible for me to obtain max 0.65 for surface skewness because wing trailing edge is very very peaked...
Do you think I will have convergence problems if I try to solve the case with similar volume-cells skewness?

udayrg · February 18, 2010, 03:39

Hi sarav

Yes certainly as your flow will be compressible flow. And flow over the wing are transonic kind of flows.

uday

sarav · February 18, 2010, 04:37

Hi!
I checked the surface mesh, cells on the trailing edge have skewness less than 0.6. Which could be my problem so?
thanks!

udayrg · February 18, 2010, 05:35

Hi sarav
Check the worst elements those are in the prism by display cells quality.
Prior doing it it plot a histogram of cell skewness between 0.9 to 1 with 10 equal parts.

And then i would like to know how are you managing the trailing edge prism nodes.

In other words the the prisms traveling from pr. side and suction side meet at the trailing edge how are you modeling the prisms there.

Uday

sarav · February 18, 2010, 06:21

Hi uday.
Well I've done the plots.
I find in the fluid zone only one cell over 0.99. Instead in prism-cells I find zero cell over 0.97. I set the two plots as attachments.

I'm managing the prism over the trailing edge as the rest of the wing...that is to say, for example in my last try, with 10 layers with linear growth of 0.1 of slope and first height of 0.5.

Can I menage the prism in a particular way only on the edge?

thanks

sarav

udayrg · February 18, 2010, 06:36

Hi sarav send me your mesh file

My mail id is udayrg@gmail.com

I will look into it and suggest you and to some extend try to finish the meshing may be upto prisms.

Uday

sarav · February 18, 2010, 07:06

Hy uday,
sorry but I can't send you the geometry.
I set as attachment a view of the problematic cells, hoping that you could understand the problem from this view.
thanks
sarav

udayrg · February 18, 2010, 07:28

Okay sarav

1)Refine the surface mesh at the trailing edge region before prism generation
2)I would suggest to put a very small surface at the trailing edge instead of edge. i.e. a very negligible width plane surface and mesh it minimum one element. And then you wont be having any problems generating prism layers on it.

I am afraid that the solution (1) alone. It not difficult however you will have to try number of times with grid refinement at the trailing edge. and You can play with shrinkage option for prism layers.

Uday

sarav · February 18, 2010, 08:28

Ok I try to refine the surface mesh, and eventually I will modify the geometry in future...
For shrinkage options do you mean "keep first layer offset", gap factor and so on?
thanks again, you are very kind!

wadebogs · March 3, 2010, 16:24

Try "minimum height" growth method instead of "uniform"

Use Mesh -> Tools -> Auto node move after creating the prisms to locally smooth bad cells.

dvb018 · September 9, 2010, 10:57

Even i am facing same problem while generating prisms & my surface skewness is 0.64 (max). What els can be done to reduce the skewness?? I am using the last ratio method in growth options.

February 17, 2010, 09:49	PRISM layer	#1
sarav New Member Join Date: Jul 2009 Posts: 25 Rep Power: 16	Hi, I've a problem generating the prism-layer with Tgrid over a 3D wing: the cell-skewness on the trailing edge is very high (more than 0.99). Who can I solve this problem? which settings do you advise me? Thanks

February 18, 2010, 06:21		#7
sarav New Member Join Date: Jul 2009 Posts: 25 Rep Power: 16	Hi uday. Well I've done the plots. I find in the fluid zone only one cell over 0.99. Instead in prism-cells I find zero cell over 0.97. I set the two plots as attachments. I'm managing the prism over the trailing edge as the rest of the wing...that is to say, for example in my last try, with 10 layers with linear growth of 0.1 of slope and first height of 0.5. Can I menage the prism in a particular way only on the edge? thanks sarav Last edited by sarav; February 21, 2010 at 04:36.

September 9, 2010, 10:57	HI	#13
dvb018 New Member Bharath D V Join Date: Sep 2010 Posts: 2 Rep Power: 0	Even i am facing same problem while generating prisms & my surface skewness is 0.64 (max). What els can be done to reduce the skewness?? I am using the last ratio method in growth options.

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February 17, 2010, 23:28		#2
udayrg Member Join Date: Mar 2009 Posts: 32 Rep Power: 17	hi sarav Make sure your surface mesh quality is around 0.6 to 0.65 skewness. And then try to generate prism layers. Uday

February 18, 2010, 02:55		#3
sarav New Member Join Date: Jul 2009 Posts: 25 Rep Power: 16	Hi! It's impossible for me to obtain max 0.65 for surface skewness because wing trailing edge is very very peaked... Do you think I will have convergence problems if I try to solve the case with similar volume-cells skewness?

February 18, 2010, 03:39		#4
udayrg Member Join Date: Mar 2009 Posts: 32 Rep Power: 17	Hi sarav Yes certainly as your flow will be compressible flow. And flow over the wing are transonic kind of flows. uday

February 18, 2010, 04:37		#5
sarav New Member Join Date: Jul 2009 Posts: 25 Rep Power: 16	Hi! I checked the surface mesh, cells on the trailing edge have skewness less than 0.6. Which could be my problem so? thanks!

February 18, 2010, 05:35		#6
udayrg Member Join Date: Mar 2009 Posts: 32 Rep Power: 17	Hi sarav Check the worst elements those are in the prism by display cells quality. Prior doing it it plot a histogram of cell skewness between 0.9 to 1 with 10 equal parts. And then i would like to know how are you managing the trailing edge prism nodes. In other words the the prisms traveling from pr. side and suction side meet at the trailing edge how are you modeling the prisms there. Uday

February 18, 2010, 06:36		#8
udayrg Member Join Date: Mar 2009 Posts: 32 Rep Power: 17	Hi sarav send me your mesh file My mail id is udayrg@gmail.com I will look into it and suggest you and to some extend try to finish the meshing may be upto prisms. Uday

February 18, 2010, 07:28		#10
udayrg Member Join Date: Mar 2009 Posts: 32 Rep Power: 17	Okay sarav 1)Refine the surface mesh at the trailing edge region before prism generation 2)I would suggest to put a very small surface at the trailing edge instead of edge. i.e. a very negligible width plane surface and mesh it minimum one element. And then you wont be having any problems generating prism layers on it. I am afraid that the solution (1) alone. It not difficult however you will have to try number of times with grid refinement at the trailing edge. and You can play with shrinkage option for prism layers. Uday

February 18, 2010, 08:28		#11
sarav New Member Join Date: Jul 2009 Posts: 25 Rep Power: 16	Ok I try to refine the surface mesh, and eventually I will modify the geometry in future... For shrinkage options do you mean "keep first layer offset", gap factor and so on? thanks again, you are very kind!

March 3, 2010, 16:24		#12
wadebogs New Member Join Date: Jul 2009 Posts: 16 Rep Power: 16	Try "minimum height" growth method instead of "uniform" Use Mesh -> Tools -> Auto node move after creating the prisms to locally smooth bad cells.