Developments of low-noise contractive nozzle used in acoustic wind-tunnel

摘要

The object of this study is to decrease background aerodynamic noise in a measuring section of acoustic wind tunnel in which the air-flow velocity is 20 to 80 m/s. ^Some aerodynamic noise sources around the measuring section in an acoustic wind-tunnel were experimentally studied, and the contribution of each source to background aerodynamic noise were elucidated. ^In the measuring section of a general acoustic wind tunnel, the dominant aerodynamic noise sources for background noise are vortex-releasing sound from the nozzle edge, jet flow noise, and boundary layer sound on the diffuser. ^Therefore, the performance of the contractive nozzle is important for developing quieter acoustic wind tunnels. ^Some methods for decreasing aerodynamic noise from nozzle blowing subsonic flow are investigated. ^The background flow noise in the measuring section is decreased by about 6dB(A) by installing many small, slender semicones on the inside surface of the nozzle end. ^(Author)