Acoustic characteristics of an isolated tiltrotor model in the DNW

An acroacoustic wind funnel test was conducted using a scaled isolated tilt rotor model consisting of a single rotor and nacelle. Acoustic data were ac quired 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 par ametric variation of rotor angle-of-attack, tunnel speed, and rotor thrust. Acoustic metrics were examined to show trends of impulsive noise for the p arametric variations. BVISPL maximum noise levels were found to increase wi th angle-of-attack (alpha) for constant advance ratio (mu) and thrust coeff icient (C-r), although the maximum BVI levels were found at much higher alp ha than for a typical helicopter. BVISPL levels were found to increase with mu for constant alpha and C-T. BVISPL was found to decrease with increasin g C-T for constant alpha and mu, although BVISPL increased with thrust for a constant wake geometry. Acoustic metrics: were also scaled for M-tip to s how simple power law scaling could be used to correct acoustic metrics for small M-tip excursions.