CFD, Giving Our Prototype Machinists a Break
Computational fluid dynamics, of CFD, was a central focus of recent industry events, and I find the topic keeps cropping up in mil/aero discussions of late. In fact, CFD simulation tools are increasingly being employed by military prime contractors (aka, primes) to meet contract requirements, such as survivability in extreme environments and temperatures, compact size, and low cost.
“Not surprisingly CFD has become a cornerstone of aerospace mechanical design. With CFD simulation, manufacturers can greatly reduce the cost of getting a product out to market. For example, instead of testing multiple physical prototypes, design engineers can simulate and test multiple variations of the design in a fraction of the time and cost,” explains Dr. Erich Buergel, general manager, Mechanical Analysis Division, Mentor Graphics.
Engineers at Azonix, a division of Crane Co. and a provider of highly engineered computers and displays for extremely harsh environments, used Mentor Graphics’ FloEFD to reduce the number of thermal prototypes required (from up to 12 to 1) when designing its new Terra embedded computer.
The Terra is an embedded computer designed for use in the transportation industry that is, like other Azonix products, completely sealed from the elements and designed for use in very hot environments.
Azonix engineers used their CAD geometry with FloEFD and defined the heat dissipation sources, material properties, and the ambient temperature outside the enclosure at the product’s design limit of 60 degrees Celsius. They then defined the goals and performed a thermal simulation. The software analyzed the CAD model, automatically identified fluid and solid regions, and defined the entire flow space without user interaction and without adding extra objects to the CAD model. The software generated simulation results in roughly five minutes. The results revealed that temperatures on the surfaces of key components exceeded the allowable limit of 90 degrees C.
The conduction paths from the heat dissipating components to the heat sink and heat sink geometry were the primary design parameters that offered an opportunity to improve thermal performance. The cross-section of the heat spreader was increased and changed from aluminum to copper. Gap-type thermal interface material was inserted at the interfaces between the components and the heat spreader. The thermal interface material was modeled as a contact resistance, reducing the number of cells, rather than conduction through material.
These changes substantially reduced the surface temperatures on the dissipating components, though still not enough to meet the thermal requirements. Azonix designers then optimized the design of the heat sink. After roughly six iterations, in each case changing the spacing and height of the fins, the heat sink was optimized and the internal component temperatures held to a minimum.
“The changes to the heat sink reduced the surface temperatures below the maximum allowable levels,” say James Young, Design Engineer for Azonix. “The result was that we were able to complete the thermal design prior to building the first prototype. When the prototype was built and tested, the measurements were within 5 percent of the simulation predictions. As a result, this was the only thermal prototype that needed to be built. This is a good example of how the new generation of embedded CAD tools can save money and time by enabling design engineers to optimize the design from a thermal standpoint early in the design process.”
The above is just one example of engineers overcoming, in little time and through automated tools, design challenges in military, aerospace, and homeland security applications. CFD is a particularly hot topic these days; considering the engineering man hours (time and money) being saved with such simulation tools, it is little question why. Color this geek impressed.