Towards a semi-empirical trailing edge noise model valid for attached and separated turbulent boundary layers

The present work investigates the noise radiated by an airfoil over a large range of angles of attack, for which the boundary layer can be attached or partially separated. We propose a trailing edge noise model based on Amiet’s theory, where the spanwise coherence length and the wall pressure spectrum are evaluated based on semi-empirical models. The model predictions are compared to wall pressure and far-field acoustic measurements performed in an anechoic wind tunnel on a NACA63₃418 airfoil. At low angles of attack, where the boundary layer is attached, the best predictions are obtained with the Smol’yakov model for the spanwise coherence length, and the Rozenberg-Lee model for the wall pressure spectrum in the presence of an adverse pressure gradient. At higher angles of attack, where the boundary layer is partially separated, Bertagnolio’s model predicts relatively well the wall pressure spectrum when the separation point is estimated from the measured static pressure distribution, but underestimates the spanwise coherence length.