SimScale CAE Forum

Turbulent Pipe Flow Tutorial Questions


#1

I was reviewing the Turbulent Pipe Flow validation project and saw something that I am not quite understanding and was hoping someone could help.

If I look a the y+ plot in the Solution Fields (yPlus [node]) and based upon the chart colors I noticed that the y+ values are quite a bit below 1. More like 0.14 if I click on the wall of the pipe with the element selector. If I measure the mesh spacing from the mesh display, I get something around 4-e-4 meters which would be a y+ of about 1.4. So the mesh is showing a much larger y+ value that what the plots are showing (10x). It looks like the graphical representation is not correct. What is the explanation for this?

Also, what is the difference between yPlus [node] and yPlus when choosing the results? yPlus seems to be all 0 where as yPlus [node] has values.

Thanks

https://www.simscale.com/workbench/?pid=4019193760922383455&rru=69b3cc5d-22af-4425-8b43-1ea0186df9e0&ci=ac78fa4c-dd7e-4372-9acc-3586fd90d159&ct=SOLUTION_FIELD&mt=SIMULATION_RESULT


#2

Hi @mas985!

There is nothing wrong with y+ well below 1 if you can afford it but being at around 1 is always recommended. Also this value depends on which turbulence model you are using and which type of flow you are investigating. So that should be fine.

About the “node” question: There are two types of Data, cell data and point data . Cell data is the ‘raw’ data produced by the solver and ParaView correctly displays this by showing each cell filed with this scalar value. Point data, however, is interpolated data based upon cell data, this allows ParaView to display a more visually pleasing gradient. - Source: Post-Processing: Data Types

For the representation in the post-processing viewer let me reach out to my colleagues to make sure there is nothing broken. Will keep you up-to-date!

Cheers!

Jousef


#3

I know that a y+ below 1 is ok but what I am saying is the values on the graph do not match the calculated values from the mesh. There is a 10x difference between the two. The graph values are 1/10th the value they should be based upon the mesh layer at the wall boundary. The documentation in that tutorial even states the target is around 1 y+ which the mesh spacing is confirming. However, the y+ value graphs are indicating a value 1/10th that.


#4

Got it @mas985!

Already reported and will let you know what the issue is as soon as possible!

Best,

Jousef


#5

Also, regarding cell vs point, so which is [node] referring to? Point data? [node] data looks to be more like cell data that is in your reference.


#6

Node is equal to the smooth node data. See below:

\underline{\textbf{Node Data}}

\underline{\textbf{Raw Data}}

Best,

Jousef


#7

Thanks!