Noise generation by a finite span swept airfoil

An analysis is developed for the noise generated by a convected gust interacting with a single swept airfoil. The airfoil spans a channel with infinite parallel walls which contains a uniform subsonic mean flow. High frequency gusts, for which the noise generation is concentrated at the airfoil leading edge, are considered. The solution utilizes the Wiener-Hopf technique applied to the equations in nonorthogonal coordinates. Closed form expressions for the farfield acoustic pressure are obtained. The convected gust is assumed to be a plane wave, i.e., the lowest order spanwise mode. Because of the swept leading edge, this convected gust generates acoustic modes of all orders. At high frequencies and low Mach numbers, moderate sweep angles produce substantial noise reductions. The residual acoustic energy is carried mainly by the higher modes. The airfoil sweep also modulates the basic high frequency farfield directivity, producing lobed patterns. The angular modulation of the directivity patterns is most pronounced for the lower order modes.