BLADE-VORTEX INTERACTION NOISE OF AN ISOLATED FULL-SCALE XV-15 TILT-ROTOR

Blade-vortex interaction noise of an isolated full-scale XV-15 tilt-rotor was investigated in the NASA Ames 80- by 120-Foot Wind Tunnel. The objective was to establish the baseline BVI noise signature of a full-scale tilt-rotor and to investigate several noise reduction concepts, including blade-tip subwings, reduced tip Mach number, and the addition of a fourth blade to the rotor system. At the nominal tip Mach number of 0.691, the peak BVI levels were found to occur at a tip-path-plane angle of 4° and at the highest advance ratio tested of 0.2. The BVI noise levels were found to be weakly dependent on CT/σ. As would be expected, reducing tip Mach number, either of the baseline 3-blade rotor, or in conjunction with a 4-blade rotor, was found to be an effective way to significantly reduce noise. The addition of the tested sub wings did not seem to be an effective strategy for noise reduction, and they incurred a performance penalty.