Behind the airfoil a wake region, which is similar to the transition zone between illuminated and shadow zones in optical problems, is present. In the outer region, far away from the airfoil edges and wake, the solution has a geometric acoustics behavior. The airfoil steady loading affects the noise generation at the leading and trailing edges in significantly different ways. The increase in leading edge noise scales on the local leading edge steady loading, rather than on the airfoil total lift. The trailing edge is essentially a scatterer of the leading edge noise, and here it is the airfoil total loading that affects the amplitude of the scattered field. Parametric calculations are presented which illustrate that, at high frequencies, moderate levels of airfoil steady loading can dramatically increase the noise level produced by airfoil convected gust interactions.
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