The chapter is dedicated to the noise radiated by thin airfoils in either disturbed or homogeneous flows. This includes noise produced by impingement of upstream turbulence onto a leading edge, self-noise caused by boundary-layer turbulence scattering at the trailing edge and noise due to the formation of a vortex street in the near wake. Analytical modeling is proposed in the frequency domain, based on linearized theories of unsteady aerodynamics. The same mathematical background referred to as Schwarzschild’s technique is used for all mechanisms in order that the predicted trends can be compared. In a first step the analysis is focused on the derivation of the induced lift fluctuations, acting as the sources of sound according to Ffowcs Williams & Hawkings’ analogy. The radiation properties of isolated aerodynamic wave-numbers in the sources are discussed in a second step. Next a statistical declination of the formalism is introduced, relating the source statistics to the PSD of the acoustic pressure in the far field. Finally the statistical models are assessed against experimental data.
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