Supplementary Data for Workflow for High-Quality Visualisation of Large-Scale CFD Simulations by Volume Rendering
Creators: name: Faltýnková, Markéta
name: Meca, Ondřej
name: Brzobohatý, Tomáš
name: Říha, Lubomír
name: Jaroš, Milan
name: Strakoš, Petr
Publisher: name: Zenodo
Year: 2024

description: High-fidelity CFD simulations can easily generate terabytes to petabytes of resulting data. Post-processing of such data is not an easy task. It holds especially for volume rendering, one of the most illustrative but computationally intensive post-processing techniques.We propose an HPC-ready workflow for post-processing large-scale CFD data computed on unstructured meshes by volume rendering using matured visual effects tools. The workflow consists of five steps: (1) parallel loading of unstructured data into memory, (2) data load-balancing among available resources, (3) re-sampling unstructured data into a regular grid (voxelisation), (4) storing data to OpenVDB format, and (5) final high-quality volume rendering of the (possibly sparse) regular grid in Blender. The workflow is based on open-source libraries, where we have improved all these steps to build an effective and robust approach. Due to parallel loading and appropriate load balancing, our workflow (a) allows loading sequential databases that do not fit into the memory of a single node and (b) significantly outperforms current scientific visualisation tools in voxelisation scalability. Moreover, due to the connection to professional visual effects tools such as Blender, interactive or photo-realistic volume rendering by path tracing, which includes global illumination effects, is allowed.With the workflow, it is possible to re-sample hundreds of time steps on an unstructured mesh with 1 billion cells (tens of TB of data) to a sparse regular grid with a density of 11 billion voxels and prepare data for interactive visualisation in just a few minutes using thousands of CPU cores.

The supplementary data includes videos and images of the resulting volume rendering, along with a demonstration of interactive remote rendering in Blender. Additionally, it contains an image that shows the difference between the path tracing and ray casting rendering methods. Below is a brief description of what can be seen in the images and videos:



01_Electric Motor - volume rendering of velocity field 1.mp4Volume rendering of electric motor simulation. Colour and density are set by the velocity field.

02_Electric Motor - volume rendering of velocity field 2.mp4Volume rendering of electric motor simulation. Colour and density are set by the velocity field.

03_Electric Motor - volume rendering of vortex Q-criterion.mp4Volume rendering of electric motor simulation. Colour and density are set by the vortex Q-criterion.

04_Ball - volume rendering of vortex Q-criterion.mp4Volume rendering of ball simulation. Colour and density are set by the vortex Q-criterion.

05_Interactive remote volume rendering in Blender 1.mp4Demonstration of interactive volume rendering in Blender. The video shows how the volume density and colour can be interactively set.

06_Interactive remote volume rendering in Blender 2.mp4Demonstration of interactive volume rendering in Blender. The video shows how the volume density and colour can be interactively set.

07_Ball - volume rendering of vortex Q-criterion.pngVolume rendering of ball simulation. Colour and density set by vortex Q-criterion.

08_Stormtrooper Vehicle - volume rendering of velocity field 1.pngVolume rendering of stormtrooper vehicle simulation. Colour and density are set by the velocity field.

09_Stormtrooper Vehicle - volume rendering of velocity field 2.pngVolume rendering of stormtrooper vehicle simulation. Colour and density are set by the velocity field.

10_Pathtracer vs Raycaster.pngThe image shows difference between path tracing and ray casting rendering methods.