A run completes, you’ve checked your forces and now you want to know where pressures have changed on your model.  For this we turn to the humble delta Cp plot.  Generating a delta Cp involves processing exported CFD data from both the new simulation and its baseline.  This can be memory intensive and for large models, will take a short while to complete.

There is an alternative however.  If we already have post-processing images of two runs coloured by different variables, and we know what values these colours represent, then we can actually do some image processing to generate the delta plots.

And so, we’re pleased to announce that we’ve added a new image delta capability to bramble’s results viewer.

The image delta tool can be used to generate deltas between any two plots, so doesn’t just need to be pressure.  Currently, we can’t generate a delta between two movies, but this is definitely on our development road map.

Creating Image Deltas

Begin by select two or more runs in the Results view and select some plots to view.  Above the thumbnails is the button ‘Generate Image Deltas’.  When you select this a second window opens from which we can select which variables, views and runs we would like to generate deltas for.  You can also set the range of the palette in the resultant delta images.

image delta
creating image deltas

Once your selections have been made, press submit.  This will trigger the generation of the image deltas.  Depending the number of runs, variables and views selected, it may take a few seconds to a few minutes to process the data.  Once generated, the deltas will appear as a new variable in the postpro selections.

Time to Update Palettes?

We’ve always favoured a limited number of levels (31) in our palettes as it can help make subtle shifts in pressure more visible.  However, when it comes to delta images where the variable value is inferred from the pixel colours, a banded palette produces a lower fidelity output.

two images from cfd simulation post processing
Image deltas - image of delta image of F1 car

The images below show the difference changing to a continuous (256 levels) palette makes to both the pressure plots and the resultant image delta.

two images from cfd simulation post processing
A delta image. showing how to create an image delta

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