Calculation of Rotor Blade-Vortex Interaction Using a Multiple-Trailer Free-Wake

Analytical results of rotor blade–vortex interaction airloads are presented with two different wake models in the comprehensive analysis CAMRAD II, and these calculated results are compared with the experimental data obtained from the higher-harmonic-control aeroacoustic rotor test (HART-I) program. The HART rotor was a 40%, Mach-scaled model of the hingeless BO-105 main rotor. Two wake models used in the comprehensive analysis are the single-trailer and the multiple-trailer free-wake models. The multiple-trailer wake model shows good prediction of lift distribution, M2cn, as a function of azimuth for baseline, minimum noise, and minimum vibration cases, and shows signi cant improvement relative to the single-trailer model in prediction of the tip vortex wake geometry. Nomenclature cn = blade section normal force coef cient fcons = fraction rollup G = total strength of trailed vorticity kcons = consolidationscaling factor M = Mach number r = blade radial station rC = centroid of vorticity rG = moment (radius of gyration) of vorticity ®S = rotor shaft angle (positive aft) 0 = blade bound circulation ¿ = wake age for the trailed vortex lament ¿cons = consolidation time constan