Machine Design

Flow simulator keeps fire controller cool

Specs for the Army's new self-propelled howitzer don't allow fans on the firecontrol electronics.

CFdesign showed Sechan engineers the naturally convective flow patterns around the fire-control system. Results let them design a more efficient fin to better remove heat from critical electronic components.

Interior flow patterns would be impossible to detect in a lab. CFdesign produces accurate thermal results and finds the local film coefficient and flow results at every location within the assembly.

The Army's Paladin self-propelled Howitzer is designed to perform in climates with temperatures to 140°F.

So the design team used CFD software to evaluate several enclosure designs that would keep the electronics cool. Doing so also let them trim two prototyping cycles off the schedule. "We hit our target four months earlier than if we had relied on traditional prototyping and testing methods," says Sechan Electronics lead mechanical engineer James Smith.

"Data from thermocouples could not have conveyed the same knowledge and confidence in the design. Tests in an environmental chamber demonstrated the accuracy of the model with close correlation of temperature data," says Smith.

The chassis is sealed and shock mounted so cooling depends solely on free convection and radiation from the chassis exterior. Heat from internal electronics transfers to the chassis by conduction.

"I ran many simulations, starting with simplified geometry. Because meshing was so efficient, we progressed to more-encompassing assumptions with more detailed and realistic models," adds Smith. "For example, we initially ignored radiation and extensively defeatured the model. Additional details gradually let the model more authentically represent actual hardware and environment."

Smith used the parametric relationship between CFdesign and the native Pro/E assembly model to evaluate several alternatives. Engineers simulated heat-pipe assemblies, components, and the single-board computer frames to minimize weight while maintaining an acceptable and structural strength.

"The integration with Pro/E was essentially transparent. We were dealing with fairly complex geometries and assemblies without incident," says Smith.

Blue Ridge Numerics Inc.
(502) 243-4858
Sechan Electronics
(717) 627-4141

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TAGS: CAD Archive
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