Aeroacoustics of a wing encountering large-scale vortex gusts

Large-scale gusts in urban environments can reach magnitudes comparable to the flight speeds of low-altitude aircraft, altering the noise generation of lifting surfaces. In this work, a generic problem of a straight wing at zero angle of attack subjected to large-scale vortex gusts is studied in an anechoic wind tunnel, and the acoustic measurements and flow visualisation are conducted. The vortex gusts were generated by a pitching wing and characterized using time-resolved particle image velocimetry. The flow field results reveal that the gust ratio reaches 0.8, and the maximum integral length scale reaches 18 times the leading-edge radius. Acoustic measurements show spectral humps with a superposed tonal peak at relatively low frequencies, associated with gust-induced noise. Leading-edge noise mainly contributes to the gust-induced noise. Spectral proper orthogonal decomposition of the time-resolved flow field around the leading edge is used to analyse the tone-related noise source, indicating that various noise generation processes coexist during the interaction. An empirical broadband-noise prediction model for gust encounters at zero angle of attack is also proposed that accounts for velocity fluctuations near the leading edge.