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Post-processing

Animation tab must be enabled

To visualize CFD results, the 64-bit Animation tab must be enabled.

• Options -> Preferences -> General -> Check "Use 64-bit diagram and animation (Beta)
• Restart IDA ICE

Residuals and convergence

The residuals displayed during the simulation are helpful for indicating convergence in the calculation. However, low and/or stable residuals alone are not always sufficient to confirm convergence. Although, as a general rule, 1000 to 3000 iterations are typically sufficient in IDA ICE CFD, depending on the complexity and mesh size of the case.

Under the heading "Review residuals and sensor values" below there is a description of how to open plots of the simulation residuals and sensor data (e.g. velocity magnitude and temperature). These plots are additional tools for evaluating convergence.

CFD report

Double-click a case in the table on the right to open the CFD report. 

Local Measuring volume

If a local volume is of interest, a measuring volume must be added in IDA ICE before running the CFD simulation. Its result will be in the CFD report.

• Open the floor of the desired zone.
• Drag and drop a Measuring Volume onto the floor.
• Adjust its properties as needed.
• Double-click the volume object to set the minimum and maximum Z-values.

Mesh inspection

• Select the case you want to visualize. Click on button "View".
• Choose "CFD Mesh" under "Animations", top left. Inspect surface mesh and placement of e.g. air terminals on boundary surfaces.
• "Look inside" the mesh using keys "Alt+C" or by using cuts described below. Keys "Alt+C" only visualize the surface mesh, cuts enables inspection of the volume mesh. 

Mesh warnings

Mesh warnings under “Current Case Info” in the CFD tab indicate that some mesh cells are of poor quality, often because they are more skewed than the default limits. Visually inspect the mesh in the Animation tab. A poor-quality mesh can, for example, cause a simulation to fail. Usually, a single warning does not pose a problem to the solver, whereas two or three warnings are sometimes fatal.

Create cuts

Bug regarding cuts - Animation Tab Bug and Workarounds

Creating a cut (result slice) of CFD results to visualize a variable cause a crash if the specified cut level is outside the CFD domain (i.e., outside the room).

Workarounds, do one of the following:

• When reviewing the mesh in the Animation tab, ensure that all cut levels for x, y, and z are within your CFD domain (the room). After that, you can visualize CFD results.
• Alternatively, in an Animation (within the Animation tab, and not the CFD Mesh), before visualizing a CFD variable (when “No scalebar variable” is selected), make sure all cut levels for x, y, and z are inside your CFD domain (the room). Then you can visualize CFD results.

If the Animation tab crashes, do one of the following:

• Delete the Animation (by default there is only one) under Outline → Animations → Animation.
  • Right-click and select Delete.
  • In the error message, choose Abort.
  • In the Animation tab, click the + button to add a new Animation.
• Alternatively, save your project and restart IDA ICE.

Create cuts

• Use x+, x-, y+ etc. bottom right for cutting the domain and inspect the refinements of the visualized mesh.
  • Press Ctrl key and hold it and drag the cut plane to a new position.
• Custom cuts is accessed through button "…". Two options for custom cuts are available via checkboxes in the form:
  • Normal vectors (x,y,z) for creating cut planes.
  • Reference surface. Via button "…" choose a surface of interest.
  • Use the buttons c+ or c- for activating each custom cut plane setting.
  • The "Bring cut to focus" sets the x, y or z cut to your focus point.
    • Set a new focus point by pressing key "F". Start by first left-clicking once in the animation view to activate it. The focus point is the point which you rotate around.
    • When the Animation is active - you have left-clicked it - you can also use keys "Alt+F" to bring the cut to the focus point.
• The "Cut level" in bottom left is the same coordinate system as the Floor plan tab.
• To hide the red border rectangle tool, press Ctrl.

Visualization of simulation results

• Choose "Animation" under heading "Animations".
• Under "Simulation" the same simulation used as input in CFD tab must be selected in order for CFD variables to become visible under "Variables".
• Select variable to visualize under CFD in the table to the left.
• Problems? Use "Refresh" under "View" in upper toolbar - if that doesn't work, reload from the CFD tab by pressing "View" again.
• Cut the domain as described earlier.
• Button "Show…" has options to:
  • "Zoom extents"
  • Set the view to different default views (top etc.)
  • Saving a view - reuse the same view for your result presentation.

Saving views and result slices (cuts)

Saving a view means that you save the position "of the camera". It will not save a result slice (a cut). Save a view by pressing "Show..." and click "Save view". The view is then stored under Show... -> Set view -> Custom 1. Every new saved view will be stored with a new number (Custom 2 etc.). Use Alt+1, Alt+2, Alt+3 etc. for keyboard shortcuts for viewing the different saved views. 

Save a result slice, a cut, by pressing key "p". To activate the Animation window you sometimes need to left-click in the tab window. You can also open button "..." in bottom left corner and press the button "+" next to "Result slices (p-key)". In this menu you can also hide and show, and delete, result slices.

Scale bar and its values

• "Auto" shows the full range of min and max values.
• "On surface" enables surfaces other than the cut plane.
• The velocity of air is per default always zero on surfaces in CFD.
• Scalebar color options is an aesthetic aspect. In some cases, one color scheme may make the results clearer than another.
• Cell data is an effective tool for understanding the results. This option displays each cell value without any smoothing - showing the real and perhaps raw calculations.
• # (number) of colors enables effective presentation techniques for the results. Each color represent one data range.
• Changing visualized min and max values enables the user to inspect and visualize the issue of interest.
  • For velocity magnitude issues in projects, an example is to test Min value 0 and Max value 1.2 m/s. Number of colors set to 8. This will create a color change in the result for air speed of 0.15 m/s. 
• "Treshold" visualize the parts of the domain that has the treshold value or higher. E.g. all cells with higher air speed than 0.2 m/s.
  • Enable by entering a value.
  • Disable treshold by setting the value to the highest possible (the value of "Max") or the lowest possible (the value of "Min").

Show and edit vectors

• Key "v" will drop a velocity vector visualization onto the currently active (recently created) surface.
  • If there is no active surface, nothing is done.
  • Shift-v Hides all vector visualizations.
  • Keys L & Shift-L shrink and grow present vectors respectively. Note that generated vectors might be too small to be seen. Try Shift-L a few times, and they will show up.

  • To change density of vectors; press button "..." in the bottom left. Then change value of ρ, chose between 1, 2, 3, 4, 5. In this menu you can also hide and show vector planes, as well as delete them.

Revive your case for Animation tab

• If IDA ICE has been closed and you want to view the CFD results later, follow these steps:
  • Click the "Refresh" button located to the right of the CFD Sessions table.
  • Sometimes you also need to manually start a Session. Do so by opening blue text "Session" and press "Launch session".

Review residuals and sensor values

• Residuals and sensor plots are available by right-clicking a case and opening "Explore case on backend".
  In the top of the window that opens, click "Residuals..." or "Sensors..." to review the plots.
• During the simulation, you can review residuals and sensor data, but you need to press F5 to refresh the plots while the iterations are running.
• If you open a saved case, you need to reconnect to the backend. To do this, press Run, but set the number of iterations under "Mesh and solver" to match the number of iterations already simulated for the case (under "Current case info"). After that, the data will be accessible on the backend.
• CO₂ emission values in plots in the backend are excluding the ambient CO₂ emission level.

• Sensors needs to be inserted before the CFD simulation. Read the heading "Sensors as measuring probes" on this page to learn how to insert probes.

Advanced - inspect the case on the backend - the raw data

NB! Cases on the backend are removed after 48 hours. Saving your file in IDA ICE and saving the CFD cases will save your backend data.

• The case is available on the backend directly after a simulation. All saved projects are available in a saved folder.  
• Make sure that the case long name in CFD tab table is the same case you are inspecting on the backend or in your saved files. An example of a case long name, in red rectangle, shown when hovering over a case:
  

Residuals

• Backend: Right-click case and click "Explore case on backend" -> postProcessing/ -> idaResiduals/ -> View.
• Saved files: Right-click case and click "Explore saved" -> postProcessing -> idaResiduals -> Open file

Sensor points (probes) - for assessing convergence

For data about velocity and temperature:

• Backend: Right-click case and click "Explore case on backend" -> postProcessing/ -> Zone_sensor/ -> 0 -> View (for T and U). If the simulation is paused and restarted, the data is in more than one folder.
• Saved files: Right-click case and click "Explore saved" -> postProcessing -> Zone_sensor -> 0 -> Open files for T and U. If the simulation is paused and restarted, the data is in more than one folder.

The Introduction Exercise - Post-processing

• Save the file when the simulation is completed.
  • Click Yes to saving the CFD cases.
• Left-click the button "View". 

Visualization of the results

• Click on "x+" in the bottom left. This will cut the mesh and show cell sizes.
• Press left mouse button and move mouse to rotate the model.

• Press key "Ctrl" and hold, use left-click and drag the cut plane as you wish.
• Click on button y- and enter Cut level 2 (m).
• Click on "Animation" in the table.
  • Click on "Air speed" under "CFD" in "Variables".
  • Press "x+" again if the cut plane is not active.
  • Set "Max" value to 0.25 (m/s) and "Min" value to 0 (m/s).
  • Place cut plane in the center line of the occupants.
  • Set "# of colors" to 10.

• Move the cut plane to 25.4 (m).
• Press button "..." to open menu "Cut properties".
• Press "+" to add vectors in the current cut plane (x = 25.4 m).
• Set ρ to value 2 (density of vectors is an integer between 1 and 5).
• Left-click in the Animation window (makes it active).
• Press keys "Shift-L" multiple times to enlarge vectors if they are not visible. Only key "L" will shrink vector sizes and "Shift-L" enlarges vectors.
• Move back the cut plane to x=25.3

• In table for "Variables":
  • Press "Air temperature".
  • Set value for "Max" to 22 and value for "Min" to 19.

• Check the box for "Cell data". This is the actual discretized calculation and illustrate each cell value.
• Uncheck "Show" for the vectors in the "Cut properties" menu - this will hide all vectors.
• Move the cut plane away from the person; press "Ctrl" and hold and move the plane with left-click and move the mouse.
  • Look at the difference in air velocity.

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Residuals and sensors

Sensors added to the IDA ICE model are picked up and carried to the CFD case. A sensor on the CFD side differs from the IDA ICE model sensor in that it samples data for more than one field but it does not register every iteration. Specifically it samples velocity (U [m/s]), temperature (T [Kelvin or Celsius]), and carbon dioxide (CO2 [concentration]).

• Go to tab CFD, right-click the case and open "Explore case on backend".

• Open "Sensors..." and after that "Residuals...".

  • Ideally, all measured values from the sensors should be identical for each iteration in a steady‑state calculation. Also ideally, all residuals should be zero, but as a rule of thumb a value of 0.001 is often considered acceptable.

In the image below, the simulation was extended to 3000 iterations.

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