[Mikado]

Hello,
I am trying to count how many streamlines reach a certain area in my domain in CFD-Post.

So far I have defined two expressions to do this. One that defines the area such as number 2: if(X>0.9[mm],if(X<0.92[mm],1,0),0) and one that counts: countTrue(number 2)@Streamline 1. However, this approach does not seem to work properly. For a very small area near the start or the end of the streamlines the counted streamlines are correct. For any area in between to little streamlines are counted. I think this is due to the way countTrue works, but I am not sure how this actually counts the streamlines. With a finer grid the results tend to be a bit more accurate but still not accurate enough.

Another approach for this problem is to count the streamlines by exporting the data and counting them in Excel or Python. This approach is more accurate I think, but I am not sure if it will work for say 10000 streamlines.

Can someone explain how countTrue counts in this case and maybe if there is a way to make the first approach work? Or should I move on to the second approach?

Thanks in advance.

[ghorrocks]

Are you sure you are doing this the best way?

Why not use a additional variable as a convecting scalar which starts from where the streamlines start, and rerun the solver. In post processing you just need to do an area integral of the scalar at your surface. It is much simpler and will be resolved at full grid resolution, rather than being only as accurate as the number of streamlines you draw.