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Machine Design

All the better to hear incoming rounds

U.S. Marines should be able to hear shouted orders perfectly when they storm their next beachhead.

The reason: Their armored landing craft will have ventilation fans that run at a relatively quiet 85 dB. Engineers at Fairchild Controls Corp. designed the fans using CFX software from Ansys Inc., Pittsburgh ( CFX BladGen and TurboGrid created and analyzed 3D models of numerous blade configurations. Team members say the software let them streamline their work and finish in 14 months.

The landing craft had been designed so its basic size and shape could not change. Airflow qualities were set for cooling a crew and electronic gear on a 125°F day. Fan noise had to be at or below what the human ear could tolerate for a day without protection.

The team replaced the original fan's fast but loud axial vane design with a slower, mixed-flow version with rotating and stationary elements. The software let engineers simulate performance and explore what-if scenarios under various operating conditions. The performance from a working prototype essentially matched data generated in simulations.

The blades, fan, and flow streams were generated in several modules of CFX fluid flow software from Ansys Inc. Engineers at Fairchild Controls decided to include a set of stationary blades to minimize fan noise while moving enough cool air.


The Expeditionary Fighting Vehicle, part tank and part boat, will carry 17 combatready Marines and crew over land and sea at speed to 30 mph.



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