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To learn more about the capabilities of the Nozzle Acoustic Test Rig and to find out if it can be used for your test, please, contact:

James E. Bridges

Testing Facilities
NOZZLE ACOUSTICS TEST RIG
Chevron Image 1

Scale model tests in the Nozzle Acoustic Test Rig (top) were used to optimize the chevron nozzle for a flight test on NASA Glenn’s Lear 25 (bottom). Chevron nozzles are becoming a familiar sight on commercial airliners since they are a mechanically simple way to reduce noise without significant thrust loss.

The next best thing to hearing a nozzle in flight
If an engine nozzle is noisy when it flies, no one will care how quiet it was on the ground. The Nozzle Acoustic Test Rig (NATR) is one of three test stands located inside the anechoic dome of the Aeroacoustic Propulsion Laboratory. It is unique because it can simulate a hot engine nozzle in flight.

Tests in 2001 are just one example of how useful data from the NATR can be. Researchers wanted to prove whether or not serrations in the engine nozzle (often called chevrons) could reduce noise. Half-scale models of a set of nozzles with and without chevrons were tested in the NATR, and measurements were compared against calculated sound pressure levels.

Careful analysis of the data indicated that a nozzle could be optimized to achieve a 2 EPNdB noise reduction in flight. The optimized design was built and installed on the NASA-owned Lear 25 and flight tests in Arizona proved the researchers to be right. The NATR results were closely matched by the flight test measurements for overall noise reduction and directivity.

If researchers had to rely on flight test data alone without the high-quality data from the NATR, optimizing the chevron nozzle would have been much more expensive.

Chevron Nozzle Mounted

TESTING FACILITIES
+ Aero-Acoustic Propulsion Lab
+ Small Hot Jet Acoustic
   Test Rig

– Nozzle Acoustic Test Rig
+ Advanced Noise Control
   Fan Rig

+ 9’x15’ Low Speed Wind Tunnel
+ Acoustical Testing Laboratory
SPECIAL INSTRUMENTATION
+ Particle Image Velocimetry
+ Rotating Microphone Rake
+ Phased Array Microphones
+ Rotor Alone
+ Rayleigh Scattering
+ Hotwire, Hotfilm, and Laser    Doppler Velocimetry
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NASA Official: E. Brian Fite
Last Updated: July 8, 2008


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