PICurv 0.1.0
A Parallel Particle-In-Cell Solver for Curvilinear LES
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Tutorial: A Guide to Visualizing Your Results

Table of Contents

The previous tutorials showed you specific steps to visualize the flat_channel and bent_channel cases. This guide provides a more general introduction to ParaView, the recommended tool for analyzing PICurv's output.

Here, you will learn the fundamental skills needed to explore any simulation result you generate, from inspecting data fields to creating publication-quality images and animations.

1. Understanding Your Output Files

After a successful run, the post-processor generates visualization files in the runs/your_run_name/viz/ directory. You will typically find two types of files:

  • **Eulerian Grid Data (.vts files):** These are VTK Structured Grid files (e.g., Field_000100.vts). They contain the computational mesh and any data fields that live on that grid, such as velocity and pressure. When you open them in ParaView, they will be grouped as a time series.
  • **Lagrangian Particle Data (.vtp files):** These are VTK PolyData files (e.g., Particle_000100.vtp). They contain only the coordinates of the Lagrangian particles and any data fields associated with them.

1.1. Common Data Fields

When you load a .vts file, you'll be able to color and analyze several data fields. The most common ones generated by the standard_analysis.yml recipe are:

  • Ucat_nodal: A 3-component vector representing the fluid velocity at the grid nodes. This is the primary field you will use for visualizing the flow.
  • P_nodal: A scalar representing the pressure field at the grid nodes.
  • Qcrit: A scalar representing the Q-criterion, a value used to identify vortices and turbulent structures in the flow.

2. The ParaView Interface

ParaView's interface has three key areas you will interact with constantly:

The ParaView Interface: 1. Pipeline Browser, 2. Properties Panel, 3. 3D View, 4. Toolbar
  1. Pipeline Browser (Top Left): This shows your data and any "filters" you've applied. You click on an item here to make it active.
  2. Properties Panel (Bottom Left): This is where you configure the selected data or filter. You must click the green "Apply" button in this panel after making changes.
  3. 3D View (Center): Your visualization.
  4. Toolbar (Top): Provides quick access to common data sources and filters.

3. Recipes for Visualizing Grid Data (<tt>.vts</tt> files)

Let's walk through the most common visualization techniques for the Eulerian grid data. First, open your Field..vts time series in ParaView and click Apply.

3.1. Recipe: Coloring by a Scalar Field

By default, the object is shown as a solid color. To color it by pressure:

  1. In the toolbar, find the Coloring dropdown (it says "Solid Color").
  2. Change it to P_nodal.
  3. The object will now be colored, and a color bar (or "Scalar Bar") will appear. You can edit the color map by clicking the "Edit color map" button (a folder with a rainbow).

3.2. Recipe: Creating a Cross-Section (Slice)

To see what's happening inside the domain:

  1. Make sure your Field..vts data is selected in the Pipeline Browser.
  2. Click the Slice filter icon in the toolbar.
  3. A plane will appear in the 3D view. In the Properties panel, you can drag the handles on the plane to move it, or change its Normal vector to orient it (e.g., Normal X Normal gives a slice perpendicular to the x-axis).
  4. Click Apply. You now have a 2D slice that you can color just like any other object.

3.3. Recipe: Showing Velocity Vectors (Glyphs)

To visualize the direction and magnitude of the flow:

  1. Select your Field..vts data (or a Slice).
  2. Click the Glyph filter icon in the toolbar.
  3. In the Properties panel:
    • Set Orientation Array to Ucat_nodal. This tells ParaView to align the glyphs with the velocity vectors.
    • Set Scale Array to Ucat_nodal. This will scale the glyphs by velocity magnitude.
    • Under "Scaling", adjust the Scale Factor to make the arrows smaller or larger.
    • Under "Masking", you can reduce the Glyph Mode from "All Points" to "Every Nth Point" to avoid cluttering the view.
  4. Click Apply. You can now see arrows representing the flow field.

3.4. Recipe: Tracing Flow Paths (Streamlines)

  1. Select your Field..vts data.
  2. Click the Stream Tracer filter icon.
  3. The "Seed" is the source of the streamlines. By default, it's a line. Drag the endpoints of the line in the 3D view to place it at the inlet of your domain.
  4. In the Properties panel, increase the Resolution of the seed line to generate more streamlines.
  5. Click Apply. You can now color the streamlines by velocity or pressure.

4. Recipes for Visualizing Particle Data (<tt>.vtp</tt> files)

Load your Particle..vtp time series to visualize the Lagrangian particles.

  1. Change Representation: In the Properties panel, find the Representation dropdown. Change it from "Surface" to Point Gaussian. This will render the particles as spheres. You can adjust the Gaussian Radius to change their size.
  2. Color by Velocity: Use the Coloring dropdown in the toolbar to color the particles by velocity and Magnitude.

5. Saving Your Work

  • To save an image: Go to File -> Save Screenshot.
  • To save a video: Go to File -> Save Animation. Choose your resolution and frame rate, and ParaView will generate a video file by playing through all the timesteps.

5. Next Steps

You are now equipped with the basic skills to install, run, and analyze any simulation in PICurv.

The "Getting Started" section is complete. You are ready to become a Power User. Proceed to the User Guide to begin learning how to create your own custom simulations from scratch.