Highly-swept blades are used in automotive cooling systems, in the fans of modern ultrahigh by-pass ratio engines and in counter-rotating open rotors in part in order to reduce noise emission. This work investigates analytically the effect of sweep on the free-field noise emission from the trailing edge of an isolated airfoil, as a first step towards a more complete approach dedicated to rotating blades. Firstly, Amiet-Schwarzschild's technique is extended to the case of a swept airfoil in order to assess the effect of sweep on the sound directivity generated both by a single three-dimensional gust and by the combined effect of all gusts at a given frequency. Sweep also affects the wavenumber contribution of the wall-pressure fluctuations beneath a turbulent boundary layer. This effect is studied by means of a Generalized Corcos model, which allows distribute energy in the chordwise and spanwise wavenumber ranges independently. The sound power level is found proportional to the squared cosine of the sweep angle at all frequencies. Furthermore, the role of the spanwise-wavenumber distribution of wall-pressure power spectral density in amplifying the radiated noise is investigated.
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