Computational Fluid Dynamics: Difference between revisions

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==Probing a fluid==
==Probing a fluid==
There are numerous ways to probe the cells and points of a fluid.  One is with the '''Hover Points On''' and '''Hover Cells On''' icons just above the Renderview.  Another is with the Probe filter.  Here is how to slice and probe a filter.
*'''File → Open → Examples → disk_out_ref.exo.'''.  On the '''Properties''' tab, click '''Apply'''.
*'''+X'''
*'''Filters → Common → Clip'''.  Uncheck '''Show Plane'''.  '''Apply'''. 
The '''Probe''' filter works much better with '''Auto Apply''' turned on.  This is the icon that looks like a tree growing out of a cube.
*'''Auto Apply''' on
*'''Filters → Data Analysis → Probe'''.  Now, move over '''disk_out_ref.exo''', updating the probed location with the '''p''' key.
The '''probed''' data will show in the Spreadsheet view.
[[Image:cfd_probe1.png|1000px]]


==Volume Rendering==
==Volume Rendering==

Revision as of 02:47, 13 November 2021

Visualizing Computational Fluid Dynamics

This tutorial shows common visualization techniques for cfd datasets. We will be using the dataset disk_out_ref.exo, found in Paraview under File/ Open/ Examples. It has a vector field in it called V.

Slices

  • File → Open → Examples → disk_out_ref.exo.. On the Properties tab, click Apply.
  • +X
  • Filters → Common → Slice. Apply. Unselect the Show Plane.
  • Color by: v.
  • In the pipeline browser, select disk_out_ref.exo
  • Filters → Common → Slice. Y Normal. Apply. Unselect the Show Plane.
  • Color by: pres.
  • View → Color Map Editor → Presets (the little envelope with a heart) → Turbo.
  • With the mouse, rotate the slices around so you can see both surfaces.


Cfd slices2.png


Stream Tracers - lines and tubes

  • File → Open → Examples → disk_out_ref.exo.. On the Properties tab, click Apply.
  • +X
  • Filters → Common → Stream Tracer. v. Seed Type: Point Cloud. Uncheck Show Sphere. Apply.
  • Color by: v.

Lines don't color as nicely as surfaces. Lets add a tube filter around each streamline.

  • Filters → Search. Type Tube. Apply.

Now, we want to know which directions the particles are moving. We will use a glyph filter. Note we place the glyph filter on the streamline, not the tube.

  • Select StreamTracer in the Pipeline Browser.
  • Filters → Common → Glyph. Glyph Type: Cone. Orientation Array: v. Scale Array: v . Very Important - Scale Factor select the recycle button to the right. Apply.
  • Color by: temp.
  • View → Color Map Editor → Presets (the little envelope with a heart) → Black Body Radiation.
  • Reset


Cfd streamtracer1.png


Glyphs perpendicular to a slice

  • File → Open → Examples → disk_out_ref.exo.. On the Properties tab, click Apply.
  • +X

Lets create a half slice. This will be used as the seed plane for glyphs.

  • Filters → Common → Slice. Origin 0, 0, 5. Uncheck Show Plane. Apply.
  • Filters → Common → Clip. Uncheck Show Plane. Apply.

Now, apply glyphs.

  • Filters → Common → Glyph. Glyph Type: Arrow. Orientation Array: v. Scale Array: v . Very Important - Scale Factor select the recycle button to the right. .5X. .5X. Apply.
  • Color by: v. Change Magnitude to Z.

Let's put these glyphs back into context by showing the original dataset.

  • Select disk_out_ref.exo in the Pipeline Browser. Representation: wireframe. On the Properties tab, change Opacity to 0.3.
  • Use the mouse to zoom into the glyph vectors.


Cfd slice glyph1.png


Flow in a fluid

To show a velocity profile we need to sample the dataset with a line, and then create glyphs off of this line. This can be done using a trick in ParaView, i.e., the Plot over Line filter. Note that a Resample to Line filter will be added in ParaView 5.11 or so.

  • File → Open → Examples → disk_out_ref.exo.. On the Properties tab, click Apply.

Lets sample over a line.

  • Filters → Data Analysis → Plot over Line. Y Axis. Change the Z component of the line to 1. Change the Resolution to 40. Apply.
  • Close the LineChartView.
  • In the Pipeline Browser, turn visibility off for disk_out_ref.exo.

We now have a line sampled through the fluid. Lets calculate the negative Z component of V (so it goes the opposite direction on the line from V). That way we can have two profiles, one with V, and one with Vz.

  • Filters → Common → Calculator. Change Result to Vz. Use 0*iHat+0+jHat+-v_Z*kHat for the formula. Apply.

Now we want to create two Glyphs - one from the Calculator filter, and one directly from the Plot over Line filter.

  • The Calculator filter should still be highlighted in the Pipeline Browser.
  • Filters → Common → Glyph. Glyph Type: Arrow. Orientation Array: Vz. Scale Array: Vz . Very Important - Scale Factor select the recycle button to the right. .5X. .5X. Apply.
  • Click on the Color Editor icon. Change the color to Orange. Apply.
  • In the Pipeline Browser select the Plot over Line filter.
  • Filters → Common → Glyph. Glyph Type: Arrow. Orientation Array: v. Scale Array: v . Very Important - Scale Factor select the recycle button to the right. Apply.

Let's put these glyphs back into context by showing the original dataset.

  • Select disk_out_ref.exo in the Pipeline Browser. On the Properties tab, change Opacity to 0.3.

Just to create a nice image, I'm going to split the views horizontally, and show this visualization also from the side.


Cfd fluid velocity profile1.png


Gradient, Divergence, Vorticity and and Q Criterion

The Gradient filter (Advanced Properties tab) provides Gradient, Divergence, Vorticity and and Q Criterion. Here is am example, using disk_out_ref.exo.


Cfd gradient1.png



Probing a fluid

There are numerous ways to probe the cells and points of a fluid. One is with the Hover Points On and Hover Cells On icons just above the Renderview. Another is with the Probe filter. Here is how to slice and probe a filter.

  • File → Open → Examples → disk_out_ref.exo.. On the Properties tab, click Apply.
  • +X
  • Filters → Common → Clip. Uncheck Show Plane. Apply.

The Probe filter works much better with Auto Apply turned on. This is the icon that looks like a tree growing out of a cube.

  • Auto Apply on
  • Filters → Data Analysis → Probe. Now, move over disk_out_ref.exo, updating the probed location with the p key.

The probed data will show in the Spreadsheet view.


Cfd probe1.png



Volume Rendering