The analytical approach declined in the chapter for various broadband – noise mechanisms can be understood as a post-processing technique to be associated with some flow description. It is found reliable for thin and moderately cambered airfoils provided that aerodynamic input data are available. The latter appear as the crucial point of the method. When they are provided by unsteady flow computations, the models can be applied as an alternative till full numerical methods including the prediction of the sound field can be applied at reasonable cost. The analytical method also suffers
Figure 25. Measured sound spectra of the flat plate at the Reynolds number of 4,000 at 0° and 5° angles of attack, versus vortex-shedding sound predictions. From Roger & Moreau (2010).
from limitations inherent to the necessary assumptions. The limitations are the best motivation for further developments and improvements. Among other topics, connections between the wall-pressure statistics and the mean – flow parameters in the boundary layers with adverse pressure gradients still need being elucidated for trailing-edge noise predictions. For turbulence – impingement noise, the effect of departures from homogeneity are not fully understood either. Finally, for all investigated mechanisms, including threedimensional effects related to blade geometry in turbomachines is required to accurately cover engineering applications.