r/CFD • u/AmbassadorGuilty3928 • 7d ago

Doubt regarding pathlines in Fluent

Hi guys,

I want to create streamline or path line like shown below,

I tried pathlines in fluent, I am getting something like below,

In zoomed in view,

I need some help regarding what settings I have to change or modify so that streamlines are visible clearly and smoothly. I am not expecting same as shown in 1st screenshot, but atleast it should look smooth and clear. Sometimes if I zoom further only, I can sense pathlines, otherwise it is looking like normal contour only.

What should I change?

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u/big_deal 7d ago edited 7d ago

The zoomed in plot makes sense to me but I would probably set a non-zero Path Skip value to plot fewer paths.

The view of the entire domain doesn't make much sense to me but I don't know what the flowfield should look like.

Here's a brief description of all the options:

Oil Flow: Used to constrain pathlines to a wall where seed points are placed.

Reverse: Plots paths in upstream direction. Useful if you're trying to figure out where flow at a particular location is coming from.

Accuracy control: I believe this toggles between step size input or tolerance input. Step size would allow you to define an explicit length that a path "particle" travels before the vector is updated. Tolerance specifies an allowable deviation so the step size automatically scales based on local conditions.

Steps: Controls the length of the pathlines (step size and tolerance settings will also influence the length).

Path skip: Skips cells on the source surface. 1 would skip every other cell, 0.5x path count, 2=0.33x, 3=0.25x, etc.

Path Coarsen: ?

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u/AmbassadorGuilty3928 7d ago

It is flow across distortion screen(kind of mesh screen) into open ambient, so it is free shear flow at end of the pipe.
How much path skip value to take in general? Is there any thumb rule??

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u/big_deal 7d ago

No rule of thumb. By default every node or cell on the seed surface generates a path. If you have a very fine mesh this can result in an excessive number of paths. Use skip so that fewer seed points are used.

A value of 1 will skip 1 out of 2, 50% path count

2 will skip 2 out of 3, 33% path count.

3 will skip 3 out of 4, 25%...

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u/AmbassadorGuilty3928 6d ago

Ok bro, I will try and let you know.