Computational fluid dynamics

Despite its name, fluid dynamics—the properties and conditions of flows—is at play not only in water and other liquids, but in the air and even in 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.

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.

Which is not to say meaningful models can be created by anyone with 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, an unschooled user 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.

Why choose Barr to perform CFD modeling?

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. That allows us to solve problems specific to a given client, industry, or geography. Expertise in OpenFOAM, in particular, is rare, and Barr is fortunate to have Dr. Christian Frias, PE, leading our CFD practice group. Chris, who is a past president of the Midwest OpenFOAM Users Group, has used the software since 2010 and has been instrumental in coordinating educational sessions and presentations at institutions like the University of Minnesota.

Chris 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.

The following links lead to overviews of just a few of the projects involving liquids to which Barr has applied computational fluid dynamics. Contact Chris or another of Barr’s CFD experts, shown below, to find out whether this technology can help solve a challenge your organization is facing. 

CFD modeling of stormwater tunnels

By developing a CFD model to simulate turbulent flows and pressure fluctuations in mixtures of air and water, our CFD specialists were able to simulate the tunnel system’s hydraulics and evaluate two causes of geysers: surges in water pressure (known as transient flows) and the presence of large pockets of air that can become entrained, or trapped, in the water and lead to explosive releases at the surface.

Learn more

CDF modeling for spillway replacement

Barr’s computational flow dynamics (CFD) experts used a program called FLOW-3D to develop a model that informed hydraulic design of the primary spillway. CFD simulations helped us predict flow patterns through the spillway’s curved approach channel and measure the impact of “superelevation”—the rise in water surface at the outermost point of the curve.

Learn more