On the impact of turbulent inflow and crack-induced blunt trailing edge on the flow field and far-field noise of an airfoil

An experimental investigation is carried out to characterize the physical mechanisms by which a trailing-edge crack, idealized as a rectangular cavity to represent delamination damage, affects boundary layer development, coherent vortex shedding, and far-field noise of a National Advisory Committee for Aeronautics 0018 airfoil. Both clean and turbulent inflow conditions are considered to isolate the role of inflow disturbance in modifying these mechanisms. The primary objective is to gain insight into how a geometrical discontinuity at the trailing edge alters the coupled aerodynamic and aeroacoustic behavior. Far-field acoustic measurements and near-wake velocity field data are obtained in the anechoic wind tunnel at Delft University of Technology. Acoustic data from a phased microphone array (from prior work) are combined with new velocity field measurements using particle image velocimetry. The results reveal that increasing crack size leads to enhanced near-wall velocity gradients and stronger coherent vortex shedding, resulting in higher tonal noise levels, particularly at higher frequencies. Normalized tonal frequencies agree with the empirical prediction model of Brooks, Pope, and Marcolini for blunt trailing-edge noise, affirming the relevance of this model even in the presence of geometric imperfections. Under turbulent inflow, the coherent structure scale diminishes slightly, and the tonal frequency increases in the trailing-edge noise spectrum, indicating that inflow turbulence modifies the vortex shedding dynamics and should be accounted for in predictive models. This study is a first step toward understanding and modeling trailing-edge noise in the presence of structural damage, under varying flow conditions.