Sensitivity of Helicopter Blade-Vortex-Interaction Noise and Vibration to Interaction Parameters

Abstract

An externally imposed vortex is allowed to interact with a rotor, and the effect of variations in individual key blade-vortex-interaction (BVI) parameters on BVI noise and BVI-induced vibratory hub loading is numerically evaluated. The interaction parameters considered are as follows: 1) vortex strength, 2) vortex core radius, 3) blade-vortex miss-distance, 4) angle of interaction in the blade-shaft plane, 5) angle of interaction in the rotor disk plane (parallel vs oblique interactions), 6) spanwise location of the interaction, 7) spanwise length of the interaction, and 8) blade lift at the time of interaction. The results indicate that an increase in miss distance and interaction angle in the blade-shaft plane and a decrease in the interacting vortex strength are most influential in reducing BVI noise and BVI-induced vibratory hub loading. BVI noise and vibratory hub loading were found to be more sensitive to changes in blade-shaft plane interaction angles than disk plane interaction angles, suggesting that introduction of a modest amount of anhedral/dihedral might be more advantageous than introducing comparable amounts of sweep in the outboard regions of the blade. It is also suggested that vibration reductions obtained for the minimum vibration schedule in the HART test result from an increased interaction angle between the blade and vortex in the blade-shaft plane and have little to do with reduced miss distances.