y+ contour plot through flow domain

Katha · July 20, 2017, 06:28

Hello,

I was trying to create a contour plot of the yplus value at an arbitrary plane throuh my flow domain.
Therefore what I did is creating the according plane, then creating a contour plot with the beforehand created plane as the location and Yplus as the variable with local/global range.
If I choose any other variable than Yplus - like pressure, density, ... - I see the expected contour plot. Once I pick Yplus the plane/contour simply disappears, whereas I do see the legend with the a value range. (0 to 1.88)

I have naturally checked for tutorials but couldn´t find any fault in my procedure also since it is a pretty basic problem as far as i can tell.

worth mentioning: It is also possible to color a plane directly using a certain variable. This methods results in CFX displaying the according plane in grey colour except very close to the walls which are coloured.

I appreciate any hints regarding this.

Regards, katha

urosgrivc · July 20, 2017, 07:11

Hi

This was a topic meny times here on the forum, so you could search it.
And this is a comon but simple problem to people geting into cfd.

Y+ value only aplies to walls there is no y+ value further from the wals so everithing is grey (no value) but you see values in the first element from the wall this is vhere y+ is relevant and imortant.
So only first element from the wall is coloured.

ghorrocks · July 20, 2017, 07:40

Yes, this question has been asked a few times. Can you add it to the FAQ page? https://www.cfd-online.com/Wiki/Ansys_FAQ

Katha · July 20, 2017, 08:29

hi,

thx for the answers, well I dont know, why I didnt find it. Of course I know, that y+ is a value only relevant to the wall, nevertheless I have used other software before and therefore know, that it is possibly to create such a contour plot in fluent for example.
The reason I was trying to plot it is since I thought it could be useful in optimizing the mesh as it could reduce the number of iterations by knowing that for example my third layer had a ceratin y+ that I desire.
Anyways thank u for the quick reply.

ghorrocks · July 20, 2017, 08:35

If you draw contours of the wall boundary objects rather than the cross section plane you will get a useful plot. I think that is what you are trying to do. You can do this as y+ exists everywhere on a wall boundary, of course.

Katha · July 20, 2017, 08:38

ja, that was the first thing I did of course. As I said my aim was to reduce the amount of times I would have to change the mesh (which is rather large therefore grid generation takes time) by seeing how the y+ looks like in the third/fourth layer and then estimating the according cell height.

July 20, 2017, 06:28	y+ contour plot through flow domain	#1
Katha New Member Join Date: May 2015 Posts: 19 Rep Power: 11	Hello, I was trying to create a contour plot of the yplus value at an arbitrary plane throuh my flow domain. Therefore what I did is creating the according plane, then creating a contour plot with the beforehand created plane as the location and Yplus as the variable with local/global range. If I choose any other variable than Yplus - like pressure, density, ... - I see the expected contour plot. Once I pick Yplus the plane/contour simply disappears, whereas I do see the legend with the a value range. (0 to 1.88) I have naturally checked for tutorials but couldn´t find any fault in my procedure also since it is a pretty basic problem as far as i can tell. worth mentioning: It is also possible to color a plane directly using a certain variable. This methods results in CFX displaying the according plane in grey colour except very close to the walls which are coloured. I appreciate any hints regarding this. Regards, katha

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July 20, 2017, 07:11		#2
urosgrivc Senior Member urosgrivc Join Date: Dec 2015 Location: Slovenija Posts: 365 Rep Power: 11	Hi This was a topic meny times here on the forum, so you could search it. And this is a comon but simple problem to people geting into cfd. Y+ value only aplies to walls there is no y+ value further from the wals so everithing is grey (no value) but you see values in the first element from the wall this is vhere y+ is relevant and imortant. So only first element from the wall is coloured.

July 20, 2017, 07:40		#3
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	Yes, this question has been asked a few times. Can you add it to the FAQ page? https://www.cfd-online.com/Wiki/Ansys_FAQ

July 20, 2017, 08:29		#4
Katha New Member Join Date: May 2015 Posts: 19 Rep Power: 11	hi, thx for the answers, well I dont know, why I didnt find it. Of course I know, that y+ is a value only relevant to the wall, nevertheless I have used other software before and therefore know, that it is possibly to create such a contour plot in fluent for example. The reason I was trying to plot it is since I thought it could be useful in optimizing the mesh as it could reduce the number of iterations by knowing that for example my third layer had a ceratin y+ that I desire. Anyways thank u for the quick reply.

July 20, 2017, 08:35		#5
ghorrocks Super Moderator Glenn Horrocks Join Date: Mar 2009 Location: Sydney, Australia Posts: 17,854 Rep Power: 144	If you draw contours of the wall boundary objects rather than the cross section plane you will get a useful plot. I think that is what you are trying to do. You can do this as y+ exists everywhere on a wall boundary, of course.

July 20, 2017, 08:38		#6
Katha New Member Join Date: May 2015 Posts: 19 Rep Power: 11	ja, that was the first thing I did of course. As I said my aim was to reduce the amount of times I would have to change the mesh (which is rather large therefore grid generation takes time) by seeing how the y+ looks like in the third/fourth layer and then estimating the according cell height.