The Radiation of Sound From an Airfoil Immersed in a Laminar Flow

Abstract

The results of an experimental and analytical investigation of sound generation by single airfoils are presented. Airfoil sections studied were representative of those used in modern axial compressors; included were modified 65 series and double circular arc profiles. The radiation of sound from the airfoil immersed in the potential core of a free jet discharging through an acoustic chamber was measured. Acoustic data were obtained for the velocity range 200 through 800 ft/sec. Measurements of wake correlation volumes and turbulence velocity components were used in an analytical model to predict the spectrum of the sound radiated by the airfoil. Sound generation was found to be dependent upon the square of the component of turbulent velocity normal to the airfoil chord. In the velocity range 300 to 800 ft/sec, the overall sound pressure level was found to be dependent upon free stream velocity to the sixth power. A correlation of the normal component of turbulent velocity was found to exist with the momentum thickness of the wake.