Sound radiated from a single airfoil and a cascade of airfoils in three-dimensional gusts is directly calculated. Euler’s equations are linearized about the mean flow of the airfoil or cascade. The velocity field is split into a vortical part and a potential part. The latter is governed by a single nonconstant-coefficient convective wave equation. For a single airfoil, the radiated sound is calculated using Kirchhoff’s method from the mid field of the unsteady pressure obtained through the unsteady aerodynamic solver. The results indicate the importance of the contribution of the quadrupole effects to the sound field. For a cascade of airfoils, the acoustic pressure is directly obtained by solving the partial differential equation. The results show that, as the maximum Mach number on the blade surface nears unity, there is a significant rise in the local unsteady pressure, and also a significant increase in the upstream acoustic pressure.

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