Adding an Isosurface


The last of the post-processing visualization options of in:Flux that has yet to be mentioned, is the isosurface. An isosurface is a three-dimensional region representing the value of a specific variable in the simulation. For in:Flux this visualization is typically used to indicate regions of specific concentrations of gas shown as percent volume, percent LFL, or percent UFL. However, several other variables can also be shown.


In this tutorial a 100% LFL and a 50% LFL isosurface will be added.


  1. Click the Add Item tab and select Isosurface from the dropdown menu.

  2. Leave the name to its automatically generated one.

  3. Select the HP Release 01 on Westerly, 5 m/s as the Simulation.

  4. Set the Variable to be METHANE Volume Fraction, % LFL from the dropdown menu. Notice that there are several other variables to choose, ranging from velocity magnitudes to temperature values. You may also choose the Flammable Gas Volume Fraction, %LFL here for the same result. This variable (described more here) looks at just the flammable components of the gas release, as this dispersion is a pure methane leak the results will be the same. 

  5. Enter a value of "100" as the %LFL Value.

  6. Set the color to be Red by selecting the red swatch () from the available color palette dropdown menu.

  7. Click the Add Item button to add the 100%LFL isosurface to the project. Your 3D window should show the red isosurface of the plume that is pointing away from the large tanks and towards the walkway, similar to that in Figure 16 below.


    Tutorial 2 - Image 16 - The 100% LEL plume from HP Release 01 dispersion simulation added to the project


  8. Repeat steps 1 through 4 above, but this time change the %LFL Value to "50".

  9. And set the Color to a transparent blue:

    1. Click the Color dropdown menu and select the blue swatch from the available color palette

    2. Click the Color dropdown menu again and click the Advanced button at the bottom of the color palette dropdown menu

    3. Four horizontal bars will appear corresponding to the red, green, blue, and alpha values of the chosen color. The alpha value represents the transparency of the object. Move the scroll bar on the Alpha channel to a value of "100" which will increase the transparency of the isosurface to be added to the project, a value of 255 will results in a sold, fully opaque, color. The color palette menu should appear as Figure 17 below.

    4. Click anywhere off of the color palette dropdown menu to confirm the transparent color


      Tutorial 2 - Figure 17 - Advanced color palette menu showing a value of 100 for the Alpha channel, making the color transparent


  10. Click the Preview checkbox  to see the isosurface is now larger and is transparent as in Figure 18 below.


    Tutorial 2 - Image 18 - Image of the 50% LFL plume from HP Release 01 dispersion simulation


  11. Click the Add Item button.


The plume has a slight bend in the westward direction due to the effect of the westerly wind traveling around the large tank. The momentum of the release has the most effect of the direction of the flow but as the distance away from the leak source increases the flow becomes more affected by the wind. If we look back at the streamwise velocity contour, we can verify that the higher wind velocities occur where the LFL plumes exist. For this example, we will move the streamwise velocity contour from its initially defined height to be at the same height as the release, 5.94 meters, to view the velocities at that height.


To edit the contour height:

  1. Select the 'Streamwise Velocity on XY plane at z = 1.5 meters' text in the Project Items tab.

  2. In the properties panel, located at the bottom left of the screen, under the Information section, change the Plane Offset value by highlighting the '1.5' text with your mouse cursor and then entering a value of "5.94" as a replacement, as shown in Figure 19 below. Note - You MUST click off the panel to verify the newly entered number.


    Tutorial 2 - Figure 19 - Indication of where to change the height of the streamwise velocity contour


  3. Click anywhere within the 3D window to confirm the new height of the contour. The contour name will change to 'Streamwise Velocity on XY plane at z = 5.94 meters' and briefly turn gray as in:Flux pulls the data from memory to update the visual.

  4. Right-Click the 'Streamwise Velocity on XY plane at z = 5.94 meters' text in the Project Items tab and select Link to Legend, as shown in Figure 20. This will change the displayed legend to reference the ranges of the contour.

    Tutorial 2 - Figure 20 - Context menu for selecting Link to Legend after user right-clicks on the contour.


  5. Turn on the visibility of the contour by clicking the checkbox next to the 'Streamwise Velocity on XY plane at z = 5.94 meters' name in the Project Items tab.



Your in:Flux window will now appear as Figure 21, verifying that higher wind velocities exist in the flow where the isosurfaces start bending. Not all of the isosurface can be seen in the image as it travels below the height of the contour's defined height. This can be resolved by changing the transparency of the contour, which will be discussed later in Tutorial 6.


Tutorial 2 - Figure 21 - Streamwise velocity contour showing negative flow (shown by dark blue regions) and faster flow (shown by orange and red regions)


Multiple contours can be added to each project and show data from dispersion cases as well as ventilation ones.


Turn off the visibility of the streamwise velocity contour and isosurfaces by clicking the checkbox next to each's name and add another contour to the project.

  1. Click the Add Item tab and select Contour from the dropdown menu.

  2. Leave the Name as its auto-generated one.

  3. In the Simulation dropdown menu, select the HP Release 01 on Westerly, 5 m/s

  4. Set the Variable to METHANE Volume Fraction, %LFL. Note that the available variables will change depending on the simulation chosen.

  5. Select XY Plane from the On Plane dropdown menu.

  6. Set the Offset at: height to "5.94" meters as we want to view the concentration at the height of the leak.

  7. Leave the Relative to: value set to Domain.

  8. Click the arrow next to Coloring and set the Range dropdown menu to User-Defined and set the Min: as "0" and the Max: to "100" as shown in Figure 22 below.

  9. Select the Add Item button and the newly added contour should resemble Figure 23 below, with the legend 'linked' to the contour.


Tutorial 2 - Figure 22 - Coloring dropdown section in the Add Contour panel setting the range to be user-defined



Tutorial 2 - Figure 23 - Contours can show information about the gas leak dispersion results as well as the ventilation information. Here the %LFL volume fraction is shown for the high pressure leak.



Note that it is not always necessary to add a contour for each case you want to view. Via the project items tab, previously defined contours can have their associated simulation switched to any simulation in the project, but not the variable it is displaying, i.e. you may change the contour to display any dispersion simulation but it will only display the %LFL volume fraction. Tutorial 6 will go over how to change the association of already defined contours and isosurfaces.