Despite its name, fluid dynamics—the properties and conditions of flows—is at play not only in water and other liquids but also in the air and the earth. In fact, fluid dynamics factors into virtually every type of change occurring on the planet, from tides, earthquakes, and weather events to the synchronized flows and swoops of starling flocks and schools of fish. It’s also a key consideration in designing structures like pipelines, flood diversions, and wind turbines.
Because flows are influenced by numerous forces of physics (for instance, pressure, speed, gravity, and temperature), understanding and predicting their dynamics is too complex a task to be solved with direct calculations. Building physical models is painstaking and expensive, and such structures can’t be easily modified to test the outcomes of altering parameters.
Enter computational fluid dynamics (CFD): the engineering specialty of using software and computer power to construct mathematical models and generate visual simulations of fluid processes.
The value of CFD
The technology’s biggest benefit is its ability to quickly and economically produce virtual prototypes and predict results with a high degree of accuracy. By allowing simultaneous testing of several design options while accounting for multiple influences, CFD offers rapid but technically sound insights into the likely results of changes to flow conditions. Engineers can also use modeling results to optimize design parameters, reduce project costs and risks, and improve regulatory compliance and long-term performance.
The technology behind CFD
How does it work? Essentially, the software dissects a 3D model of a flow into thousands or even millions of points, or “cells,” that together form what’s known as a grid or mesh. The program then assigns to each cell several mathematical equations representing the variety of physical forces affecting it, and calculates how those interacting forces affect each cell and the others surrounding it.
CFD requires so much computing power that until about 20 years ago, only supercomputers could process and synthesize the amount of data needed to simulate intricate flow scenarios. With constant advancements in microprocessors, however, CFD edged into easier reach of consultants and researchers.
The accuracy of a CFD simulation hinges on the modeler’s expertise in the type of problem being addressed.
Despite the advances in technology, however, creating meaningful models requires more than a powerful computer and certain software. The accuracy of a CFD simulation hinges on the modeler’s expertise in the type of problem being addressed. Without understanding the physics that influence air entrainment or tailings flow, for example, a novice of CFD software would obtain results useless in solving a real-world challenge involving dam-spillway energy dissipation or mine-tailings deposition. Especially with turbulent flows, it’s crucial to set precise rules and initial conditions for simulations. The effects of minor miscalculations or oversights during the early stages of model development can multiply as simulations take shape, yielding profoundly unreliable outcomes.
Selecting a CFD modeling expert
Barr’s engineers deliver highly accurate models through comprehensive analysis and interdisciplinary collaboration with academic researchers as well as internal experts. For example, in using CFD to conduct hydraulic analyses, in-house water resources specialists with field and laboratory experience in a variety of focus areas frequently come together to construct models and corroborate results. In modeling tailings flows, we often work side by side with university professors to verify model accuracy.
Another benefit we offer is proficiency in four CFD software packages: OpenFOAM, ANSYS CFX, ANSYS Fluent, and FLOW-3D. This allows us to solve problems specific to a given client, industry, or geography. Below are just a few of the projects involving liquids to which Barr has applied computational fluid dynamics.
Contact us to learn more about CFD and whether this technology can help solve a challenge your organization is facing.
About the author
Christian Frias, senior water resources engineer, leads Barr’s CFD practice group. Chris, who is a past president of the Midwest OpenFOAM Users Group, has used OpenFOAM software since 2010 and has been instrumental in coordinating educational sessions and presentations at institutions like the University of Minnesota. He is also a member of the American Society of Civil Engineers’ committee on two-phase flow in urban water systems, to which he contributes expertise in using CFD to simulate air and water mixtures in municipal water systems. The committee promotes collaboration between consultants, academics, and municipalities in creating practical solutions to water-system operational issues.
Barr’s computational fluid dynamics (CFD) specialists helped the City of Minneapolis solve the problem of stormwater “geysers” erupting on a road during especially intense rainfalls.
Following the record flood of July 2020, the state of South Dakota decided to replace the Elm Lake Dam's primary spillway. Barr was hired to conduct site investigations, assess alternatives, and identify options for replacing the spillway and upgrading the dam facility to meet modern safety standards.
Image gallery (below):
Barr's CFD model of Saint Anthony Falls dam.
Barr's CFD model of a raft ride.
Barr's CFD model of a raft ride.