Acoustic Characteristics of a Model Isolated Tiltrotor in DNW

An aeroacoustic wind tunnel test was conducted using a scaled isolated tiltrotor model. Acoustic data were acquired using an in-flow microphone wing traversed beneath the model to map the directivity of the near-field acoustic radiation of the rotor for a parametric variation of rotor angle-of-attack, tunnel speed, and rotor thrust. Acoustic metric data were examined to show trends of impulsive noise for the parametric variations. BVISPL maximum noise levels were found to increase with α for constant μ and CT, although the maximum BVI levels were found at much higher a than for a typical helicopter. BVISPL levels were found to increase with μ for constant α and CT. BVISPL was found to decrease with increasing CT for constant α and μ, although BVISPL increased with thrust for a constant wake geometry. Metric data were also scaled for Mtip to evaluate how well simple power law scaling could be used to correct metric data for Mtip effects.