"The Childe...More restless than the swallow in the skies..." -Lord Byron, Childe Harold's Pilgrimage

Friday, September 20, 2013

Returning to NASA Glenn

65 feet high
130 feet in diameter
17,000 fiberglass wedges, each 2 feet thick
3 jet engine test rigs
1,000+ degrees Fahrenheit testing conditions
Dozens of microphones
Zero echoes

The Aero-Acoustic Propulsion Laboratory



The above video showcases a far-field microphone array in the AAPL located at
NASA Glenn Research Center in Cleveland, Ohio. If the laboratory reminds you of a recording studio, it should. That is precisely what the AAPL is. (Prefer a photo tour?
Jump to my gallery.)

Microphone Arrays at NASA's AAPL

A key feature of the AAPL is the ability to measure jet engine noise from near and far. It's not enough to stand next to a running test rig and say, "Yup, that's loud." At the AAPL, scientists and engineers study a jet's noise output from multiple angles and distances, just as it is experienced in everyday life. Jets today are loud, but keep in mind they could be--and once were--much worse.

Jet engine test rigs at NASA's AAPL

Above at left is the Small Hot Jet Acoustic Rig. To the right is the larger Nozzle Acoustic Test Rig. Researchers use both to try out new and hopefully less noisy jet engine designs. They tend to focus on the engine's backside. As was explained to my tour group, one motivation for altering the back of the engine is convenience. In terms of safety regulations, it's much more troublesome to modify the front of the engine--where things get sucked in--than the back of the engine--where things get blown out.

Enough about tech issues. Let's talk about raccoons. ...yes, raccoons.

fiberglass acoustic wedges behind wire mesh

Notice the wire mesh covering the above acoustic wedges? NASA installed the mesh to keep birds from nesting in the dome. Alas, though the wire mesh solved the bird problem, it created a raccoon problem.

A few of the stripe-tailed scavengers snuck into the AAPL, took one look at the wire mesh, and decided it must be climbed. And they made it to the top. Furry critter advocates will be happy to know this story does not end with dead raccoons. Upon discovering the unauthorized visitors, NASA staff left a door cracked. The raccoons let themselves out overnight--presumably after discovering that the AAPL deprived their squeals of cool reverb.

NASA Glenn on Second Thought

A jet fan test rig at NASA Glenn Research Center
The Advanced Noise Control Fan test bed

The above cluttered photo is not my favorite. But in terms of capturing NASA Glenn's essence, it is probably the best picture I can share. Glenn's exterior is a jungle of tan bricks and weathered steelwork. It shows the blight of age and funding cutbacks. Yet when you enter its facilities, especially AAPL, Glenn becomes awe-inspiring. This is one of NASA's workhorse centers. One of its oldest buildings, dating to World War II, was originally used to troubleshoot overheating B-29 Bomber engines. Today it houses research into ion engines intended for deep space.

This was my second visit to NASA Glenn. I attended 2012's Mars Curiosity landing social. I'm already daydreaming about a third trip. The place has an industrial charm. The staff display warm hospitality. The work they do, especially in aeronautics, is critical. I encourage paying a visit. Public tours are free but limited. Advanced registration is required. Visit the NASA GRC website for details.

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