For people who live around airports, noise created by planes can cause a disturbance. Researchers at NASA’s Glenn Research Center in Cleveland, OH have been working with metallic foam that is installed around an engine to reduce noise. The firm foam, crafted from stainless steel, looks like a tightly compacted honeycomb made of silver metal, and feels uniform on the surface — gently abrasive, like a fine-grained pumice stone. “This is an open cell foam, which is mostly air. The foam is formed by ligaments — like a sponge that you use in your kitchen, except the ligaments are metal,” according to Glenn engineer, Cheryl Bowman.

A test rig is assembled at NASA Glenn to evaluate the noise reduction of a newly developed metallic foam liner. (NASA Glenn)
Glenn engineer Dan Sutliff had been partnering with NASA’s Langley Research Center (Hampton, VA) for a decade on researching aircraft noise reduction. He and a colleague developed an experiment and fine-tuned the properties of metallic foam developed at Langley. Partnering with Porvair Advanced Materials (Hendersonville, NC), they created the metallic foam with exacting properties, including the pore sizes and density that were optimal for engine-generated noise frequencies. They then installed the Foam Metal Liner over the rotor of Glenn’s Advanced Noise Control Fan, an 8-foot-long, 4-foot-diameter test fan that is about the size of an aircraft engine.

The foam reduced engine noise by more than half. The hope is that it can be used in the commercial market to reduce engine noise effectively and without increasing the operating costs or the weight and without performance penalties. The long-term goal is that all objectionable airplane noise remains within the boundary of the airport, leaving residential communities unaffected.

For more information, visit: www.nasa.gov/centers/glenn/technology/metallic_foam.html.

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