Computational Fluid Dynamics (CFD) often has the informal meaning Colorful Fluid Dynamics due to the dominance of rainbow color ramps and over the top post-processing techniques used to create flashy eye catching visuals, like the image below.
CFD is inherently a data rich analysis method with no shortage of variables to plot or complex flow phenomena to try and elucidate. The perennial challenge remains; how to best convey the results of a technical analysis?
While colored and shaded velocity vectors, fancy contour plots, or even 3D shaded volumes speak powerfully to a technical audience, the realistic rendering of generated datasets in their intended surroundings makes simulation results more inclusive and accessible to non-expert audiences. In the realm of river and hydraulic engineering, why not make water look like water?
Data Visualization and Realistic Rendering
Rendering is the process of assigning materials properties to different 3D regions, and then simulating light and shadows to create realistic images. From washing your hands in a sink to swimming in a river every person has at least a basic understanding of fluid flow from every day experiences. By having water look like water, simulation results become meaningful and recognizable.
To apply this to an engineering problem, let’s take a look at an example from a spillway CFD study. Ever since the 1970’s, the PMF or probable maximum flood is used for spillway design. The PMF represents “the flood that may be expected from the most severe combination of critical meteorological and hydrologic conditions that are reasonably possible in the drainage basin under study”1—in other words, the biggest flood possible for a given location. Dams built before the standardization of the PMF, or those located in areas with changing climate, may be at risk since it’s possible for the site to experience a larger flood event than what was considered in the original design. CFD is a good tool to simulate these extreme events to identify potential problems.
For a recent project, the primary goal was to use the 3D CFD code Flow-3D to extract pressure distributions along the spillway training wall to support a wall stability analysis for an existing spillway as well as identify if overtopping would occur for the extreme PMF event.
By having water look like water, simulation results become meaningful and recognizable.
The extracted pressure plots on their own aren’t terribly exciting, unless of course, if you like non-hydrostatic pressure distributions. I thought it would be worthwhile to create a realistic rendering as a way to visualize what this extreme event would look like to see how the water flows down the spillway.
To go about this realistic data visualization, the simulated water surfaces were extracted from Flow-3D and then imported into Blender along with the spillway solid and surrounding topography. In Blender different materials are assigned, for instance the spillway is assigned a concrete material, and the water surface is assigned a water material. Each time step is rendered and the combined in the following animation.
Realistic rendering of simulation results create powerful visuals that reach a far wider audience and serve as a tool to communicate the results of a technical analysis. This form of CFD data visualization has direct benefits to a stakeholder engage process where technical results are communicated to an often diverse group of stakeholders. Even niche fields of hydraulics like whitewater park and wave design can benefit from this form of data visualization where the ultimate product is hydraulic shape itself.
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