The Acoustic Environment of the NASA Glenn 9- by 15-Foot Low-Speed Wind Tunnel

Abstract

The 9-by 15-Foot Low Speed Wind Tunnel is an acoustic testing facility with a long history of aircraft propulsion noise research. Due to interest in renovating the facility to support future testing of advanced quiet engine designs, a study was conducted to document the background noise level in the facility and investigate the sources of contaminating noise. The anechoic quality of the facility was also investigated using an interrupted noise method. The present report discusses these aspects of the noise environment in this facility.

Directionally Sensitive Sensor Based on Acoustic Metamaterials

“…Figure 1.1: Image of the test section inside NASA Glenn's 9'×15' low-speed wind tunnel with soundabsorbing deep acoustic panels lining the walls [21]. ……………………………………………………….2 Figure 1.2: Schematic of the turbulent boundary layer with the viscous and logarithmic regions shown [23].…”

“…Beamforming results can be improved further by removing the main diagonal of the cross-spectral matrix [19]. Typical aeroacoustic measurements being performed in closed test-section wind tunnels will employ the combination of recessed microphone arrays and processing techniques like beamforming that are able to suppress the influence of turbulent boundary layer pressure fluctuations [15][16][19][20][21][22]26]. This has become a standard approach for aeroacoustic measurements, but it is not without its drawbacks.…”

“…Although, porous materials will affect boundary layer profiles requiring correction terms. Materials such as melamine and wool have been found to be successful in lowering the reflection coefficient [20][21]. An example of a wind tunnel section with acoustically treated walls is shown below in Figure 1.1 which depicts the test section inside NASA Glenn's 9'×15' low-speed wind tunnel [21].…”

“…Materials such as melamine and wool have been found to be successful in lowering the reflection coefficient [20][21]. An example of a wind tunnel section with acoustically treated walls is shown below in Figure 1.1 which depicts the test section inside NASA Glenn's 9'×15' low-speed wind tunnel [21]. The other problem facing closed test section wind tunnel measurements is the turbulent boundary layer that submerges the section walls imparts intense pressure fluctuations on surface mounted microphone arrays [16,19].…”

New modular fan rig for advanced aeroacoustic tests - Acoustic characterization of the facility

“…Furthermore, fan rigs usually support in-duct microphone arrays for unsteady wall-pressure measurements and modal decomposition [11,21]. Additionally, wind tunnel facilities with large test sections have also been used for aeroengine noise tests, which might be useful to assess fan noise from wind-cross, and angle-of-attack configurations, and innovative aeroengine architectures, such as Counter-Rotating Open Rotors (CROR) [4,14,20].…”