Acoustic source identification for transitional airfoil flows using cross correlations

Direct numerical simulations have been conducted of the flow over NACA-0006 and NACA-0012 airfoils. For all cases multiple sources of noise have been observed. At low frequencies, the contribution of trailing-edge noise radiation is significant, while for the high frequencies, the radiated noise appears to be due only to flow events in the transition/reattachment region on the suction side. Cross correlations of acoustic and hydrodynamic quantities, combined with ray-acoustic theory, are used to identify the main source locations. While the physical origin of trailing-edge noise can be clearly identified using these methods, the situation is less clear for additional noise sources that radiate at high frequency. Evidence suggests that these additional noise sources are located downstream of transition on the suction side of the airfoil, in the region directly downstream of boundary-layer reattachment.