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Swiss Army CFD

Thu, 06/06/2013 - 12:31pm
Paul Livingstone and Kerem Karakoc, Mechanical Designer, and Eric Chen, Structural Engineer, Kawa Engineering Ltd.

Once the specialized tool of aerospace corporations, CFD has become an indispensable tool for product designers and industry.

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Flow streamlines modeled using ANSYS CFD software show critical locations for a powerhouse in relation to the Haa-ak-suuk Creek waterfall on Vancouver Island, B.C. Image: ANSYS   

The first successful modeling of fluid and gas flows was accomplished by the aerospace industry, which recognized the advantages such understanding could have for successful aircraft design.

Now, the once exotic application of Navier-Stokes equations for the modeling of flows is performed on just about anything, from the world’s largest hydropower plant to a mundane rear-view mirror on a car.

The availability of computer-aided single-phase flow modeling, also called computational fluid dynamics (CFD), has prompted companies who develop these tools to expand their product line. One such company is ANSYS, Cecil Township, Pa., which offers two CFD packages: FLUENT and CFX.

CFX is a general-purpose CFD program with a highly parallelized solver that has been in industrial use for more than 20 years. Over time, the basic tools have been expanded and wrapped in an intuitive graphical user interface that allows for customization and automation.

FLUENT, meanwhile, was added to ANSYS’ portfolio in a 2006 acquisition of Fluent Inc., which was known for its own CFD solution. Already popular with engineers, FLUENT is a broad-based physical modeling tool for flow, turbulence, heat transfer, and reactions.

Applications, from modest to intractable
In recent years, as products have become extraordinarily complicated, CFD has been seen as a way to fine-tune performance of existing technologies. Turbochargers in automobiles, for example, have been steadily improving with help from CFD simulations, and are now being regularly used in pickup trucks and economy cars. The improvements have been largely incremental, but sometimes the improvements are dramatic. Polyurethane wetsuits, developed with the help of CFD tools, were banned from the 2012 Olympics because the performance advantage for swimmers was too pronounced. Too many records were broken in Beijing in 2008.

Such widespread appeal has led ANSYS to build a centralized suite, the ANSYS Workbench, to help handle the many different tools that developers want to access while conducting research. In addition to the CFD packages, simulators, workflow, and data management are all accessible through Workbench.

These improvements appeal to researchers in the academic setting as well because they give extra flexibility to the way a CFD study unfolds. Academic research, in particular, tests the limits of what CFD can do. Instead of refining an existing product, these scientists are often pushing the envelope of fundamental physical understanding.

“Out-of-the-box solution capabilities meet the needs of many CFD engineers, but most researchers are taking their complex simulations to another level,” says Wim Slagter, lead product manager, ANSYS Inc.

Academic researchers, he says, need to ensure that their solution of choice has the breadth, depth, and scale needed to accommodate their sophisticated CFD simulations.

CFD: A good fit for hydropower
Large industries, especially those involved in process technologies like steel, oil and gas, and chemicals, also benefit from CFD tools. The hydropower industry, in particular, depends on them for obvious reason. Efficient turbine operation depends on the ability to accurately understand water flow through changing conditions and time. But other aspects of hydropower operations must also account for flow, some of which might be unexpected. Every dam is designed to accommodate flooding. But even if a dam is designed to withstand and manage the worst of nature’s onslaught, the outbuildings, powerhouses, and infrastructure adjacent to the dam could be inundated. To reduce this risk, planners use CFD to determine where and how flood waters will flow in a worst-case scenario.

In a recent project that used ANSYS’ tools, a Canadian client of Kawa Engineering Ltd., Vancouver, B.C., needed to locate a powerhouse close to a waterfall in an area with minimal flood risk. If flooding did occur in the powerhouse, it would be costly. Finding a suitable location away from flooding also decreases the need for additional components to protect electrical equipment (if flooding does occur). This helps, in the end, to reduce the construction costs.

To begin their work, a Kawa Engineering designer used ANSYS CFX to create a model of the riverbed’s surface and shores, near where the powerhouse will be positioned, using data collected via laser scanning and imported into CAD software. Then ANSYS DesignModeler software helped simulate the flooding environment and determine where to place the powerhouse.

ANSYS CFD came into play when Kawa engineers used the Eulerian-Eulerian multiphase model to define the interaction between flood water and the ambient air for open channel flow. Floodwater makes an initial hydraulic “jump” as it flows through a feature like a waterfall. By running the CFD simulation on a 32-core cluster computer and repeating the simulation multiple times using different river conditions, the designers discovered the maximum hydraulic jump that could occur.

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