NASA Glenn’s Wind Tunnels and Anechoic Labs: Tools for Quieter Skies and Deeper Space Knowledge
A look at the facilities that let researchers test engine noise, flight conditions, and acoustic technologies—from low‑speed wind tunnels to indoor anechoic chambers—and why their work matters for future aircraft and space missions.
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1. 9‑by‑15 Low‑Speed Wind Tunnel
The 9‑by‑15‑Foot Low Speed Wind Tunnel is specially designed to give researchers a controlled environment to study aircraft engine aerodynamics and acoustics at takeoff and landing conditions. Major modifications completed in 2019 improved the flow and lowered the background noise of the tunnel. A new five‑sensor traversing microphone rake helps measure sound produced by scale experimental propulsors, providing data that can reduce noise for communities near airports.
2. Aero‑Acoustic Propulsion Laboratory (AAPL)
The Aero‑Acoustic Propulsion Laboratory is a dual‑purpose 65‑foot radius geodesic dome that serves as an anechoic chamber for testing aircraft engines and components. Seventeen thousand custom‑designed two‑foot‑thick fiberglass wedges line the walls and floor, absorbing sound and preventing reflections. AAPL houses three rigs: the Nozzle Acoustic Test Rig (NATR), the Small Hot Jet Acoustic Rig (SHJAR), and the DGEN 380 Aeropropulsion Research Turbofan (DART). Its anechoic environment enables precise measurement of noise from experimental propulsors.
3. Small Hot Jet Acoustic Rig (SHJAR)
SHJAR can test single‑stream nozzles up to 5 cm in diameter at Mach 2.0 and 800 K. Researchers have used the rig to develop advanced diagnostic techniques such as Rayleigh scattering, Raman scattering, digital Schlieren, and real‑time particle image velocimetry. Three‑dimensional microphone arrays map noise sources, and time‑resolved temperature measurements using Raman‑based optical methods have captured thermodynamic fluctuations needed for turbulence models. Ground‑based tests on SHJAR also identified jet‑surface interaction as a distinct noise mechanism, insights later transferred to NATR.
4. Nozzle Acoustic Test Rig (NATR)
NATR, a free‑jet wind tunnel, evaluates jet‑noise reduction concepts at conditions up to Mach 0.35. Scale models from military and commercial engines are tested, and a jet‑engine simulator with up to three air streams reproduces turbofan flow. An overhead array of microphones measures far‑field noise at all angles, allowing accurate translation to what an aircraft flying overhead would sound like. Over its 30‑year history, NATR has been the origin of many important jet‑noise breakthroughs. The chevron nozzles seen on today’s aircraft were first ‘discovered’ during a NASA‑led test campaign in 1997, and industry has used the rig to develop noise‑prediction methods for near‑term designs.
5. DGEN Aero‑Propulsion Research Turbofan (DART)
DART integrates the DGEN 380 as a flexible test bed for aeroacoustic and aero‑performance research. Recent tests (August 2019) obtained simultaneous acoustic measurements using a circumferential infinite‑tube‑probe array at the core‑nozzle exit together with sideline and far‑field microphone arrays. The resulting data set supports advanced source‑separation and phased‑array methods to elucidate core‑noise structure and propagation characteristics of other propulsion‑noise sources.
6. Acoustical Testing Laboratory (ATL)
The ATL is a versatile chamber that can be configured as an anechoic or hemi‑anechoic space. Dense rubber in the walls and ceiling reflects or absorbs external sound, while 34‑inch‑deep fiberglass wedges on the walls and floor absorb 99 % of incident sound above 100 Hz. The laboratory has quantified noise emissions from International Space Station experiments, measured electric‑motor noise, calibrated microphones, evaluated acoustic liners for aircraft‑engine models, and assessed over‑the‑wing engine placement for reducing takeoff and landing noise. Recent work included a scale model of a supersonic aircraft engine inlet and a spacecraft cabin ventilation fan.
These facilities illustrate how ground‑based testing bridges the gap between laboratory research and real‑world flight conditions. They provide the data needed to design quieter engines, improve installation effects, and validate computational models—key steps toward more environmentally acceptable aviation and space exploration.