Reflectivity characterization of in-flow acoustic floor treatment for the NASA Langley 14- by 22-Foot Subsonic Tunnel

An experimental campaign was performed to assess acoustic modifications to the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel. Recent acoustic test campaigns in this facility have emphasized the reduction of aerodynamic noise due to flow scrubbing across acoustically treated floor baskets. However, the measures implemented to address this noise contaminant have resulted in the installation of floor basket coverings of high acoustic reflectivity. Therefore, a controlled test campaign was performed to identify a suitable acoustic basket configuration in terms of both acoustic absorptivity and reduced flow scrubbing noise. This test campaign was conducted in two phases: the first in an anechoic chamber facility on a single acoustic basket panel to identify a notional configuration of acceptable absorptivity, and the second in a complete floor basket installation checkout test in the NASA Langley 14- by 22-Foot Subsonic Tunnel. Results show that the newly implemented floor treatment exhibits suitable performance in both desired categories of acoustic absorptivity and reduced flow scrubbing noise. This campaign has also validated the effectiveness and usefulness of the anechoic chamber test configuration as a means of assessing acoustic reflections at oblique angles of incidence.