The acoustics of a 10-bladed, 457 mm diameter open rotor ingesting a turbulent wake is studied. The wake was generated by a 2-inch diameter cylinder placed 20 cylinder diameters upstream of the rotor disk, and the inhomogeneous inflow was characterized by hotwire measurements. Acoustic measurements were made with microphone instrumentation placed in anechoic chambers flanking the test section and rotor. Measurements were made for 13 rotor speeds, two wake intersecting locations on the rotor disk, and two rotor yaw angles. Single microphone measurements and phased microphone array measurements were completed at all conditions. Measurements from a 251-channel microphone array with sensors divided between two anechoic chambers were used to examine the directivity of the rotor/wake interaction and to localize sound sources. Various simple beamforming techniques, variants of delay and sum, were used to investigate the distribution of the acoustic sources across the rotor disk as a function of operating condition. The array was able to distinguish the dominant source regions as a function of observer location. These regions agree with a simple leading edge noise directivity model at higher advance ratios near zero-thrust, but airfoil self-noise may be significant at low advance ratio and high frequency as well.
展开▼
